What temperature grades are available for NdFeB magnets?

NdFeB temperature grades and their maximum operating temperatures are: N (80°C), M (100°C), H (120°C), SH (150°C), UH (180°C), EH (200°C), and AH (230°C). Higher temperature grades contain dysprosium or terbium to increase coercivity.

What coating should I use for a neodymium magnet in a humid environment?

For humid or outdoor environments, nickel-copper-nickel (Ni-Cu-Ni) plus an epoxy topcoat provides excellent moisture protection. For marine or saltwater exposure, Parylene C coating offers superior chemical resistance. Bare NdFeB corrodes rapidly without a protective coating.

Radial Magnets Knowledge Base

Everything You Need to Know About Magnets

From fundamental physics to procurement strategy — a comprehensive technical reference for engineers, sourcing professionals, and product designers working with permanent magnets.

30+ Articles 7 Topic Clusters NdFeB Specialists

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Magnet Fundamentals

How permanent magnets work, key magnetic properties, and the magnetization process.

4 articles

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Magnet Materials

NdFeB, SmCo, Alnico, and Ferrite — deep dives and side-by-side comparison.

5 articles

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Shapes & Orientations

Disc, ring, block, arc, and custom geometries with magnetization direction guide.

5 articles

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Coatings & Protection

Why NdFeB corrodes and how to choose between Ni, Zn, epoxy, and Parylene.

3 articles

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Applications Library

EV motors, medical devices, sensors, aerospace, and industrial automation use cases.

5 articles

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Engineering & Procurement

How to write an RFQ, PPAP requirements, temperature grades, and safety guidelines.

5 articles

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Glossary A–Z

Definitions for 50+ magnetics terms used in engineering specs and datasheets.

50+ terms

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Magnet Fundamentals

What Is a Permanent Magnet?

A foundational guide to how permanent magnets work — from atomic-level magnetic moments to the macroscopic field that holds them in your application.

FundamentalsPhysicsBeginner Friendly

permanent magnetmagnetic domainsferromagnetismNdFeB basics

Definition: What Makes a Magnet "Permanent"?

A permanent magnet is a material that generates its own persistent magnetic field without requiring an external power source. Unlike an electromagnet — which needs continuous electrical current — a permanent magnet retains its magnetization indefinitely under normal operating conditions.

The defining characteristic of permanent magnets is their ability to resist demagnetization. This resistance is quantified by a property called coercivity (H_c) — the higher the coercivity, the harder it is to demagnetize the magnet. Materials with high coercivity are called "hard" magnetic materials, while easily magnetized (and demagnetized) materials are called "soft."

The Atomic Origin of Magnetism

Magnetism at the atomic level arises from two sources: the spin of electrons around their own axis, and the orbital motion of electrons around the nucleus. Each electron behaves like a tiny bar magnet. In most materials, electrons pair up with opposite spins and cancel each other out, producing no net magnetic moment.

In ferromagnetic materials — iron, nickel, cobalt, and certain rare-earth alloys — unpaired electrons create a non-zero magnetic moment. Furthermore, quantum mechanical exchange interactions cause neighboring atoms to align their magnetic moments in the same direction, forming regions of uniform magnetization called magnetic domains.

Magnetic Domains

In an unmagnetized piece of iron, domains exist with their magnetization pointing in random directions. The net magnetization of the entire piece is therefore zero. When exposed to an external magnetic field, domains aligned with the field grow at the expense of misaligned domains — a process called domain wall motion — until the material becomes magnetized.

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In neodymium magnets (NdFeB), the crystal structure forces all magnetic moments into specific preferred orientations called easy axes. This gives NdFeB its extraordinary coercivity — the anisotropy energy is so high that thermal vibrations alone cannot randomly reorient the domains at room temperature.

Hard vs. Soft Magnetic Materials

Property	Hard (Permanent) Magnets	Soft Magnetic Materials
Coercivity	High (> 10 kOe typical)	Low (< 10 Oe typical)
Retentivity (Br)	High	High, but transient
BH_max	High energy product	Not applicable
Examples	NdFeB, SmCo, Alnico	Silicon steel, Permalloy, soft iron
Primary use	Generate persistent fields	Guide/channel flux (cores, shields)

How Are Permanent Magnets Manufactured?

The manufacturing process for sintered neodymium magnets — the most common high-performance permanent magnets — involves several carefully controlled steps:

Alloy preparation: Neodymium, iron, and boron are melted together in precise ratios (approximately Nd₂Fe₁₄B) using vacuum induction melting.
Milling: The alloy is broken into fine powder (3–5 microns) using hydrogen decrepitation followed by jet milling in an inert atmosphere.
Pressing: Powder is aligned in a strong magnetic field and pressed — either die-pressed (axial) or isostatically pressed — to create a "green" compact.
Sintering: The compact is sintered at ~1050–1100°C in a vacuum furnace, achieving >99% theoretical density.
Machining: The brittle sintered block is cut and ground to final shape using diamond-tipped tools.
Coating: A protective coating (typically Ni-Cu-Ni) is applied to prevent corrosion.
Magnetizing: The finished part is exposed to a strong pulsed field (>3T) to magnetize it fully along its easy axis.

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Key insight: Magnets can be shipped and handled unmagnetized — making machining safer and logistics simpler — then magnetized in the final assembly using an external coil fixture. This is common practice for large or complex assemblies.

Frequently Asked Questions

What is the difference between a permanent magnet and an electromagnet? ▼

A permanent magnet retains its magnetic field indefinitely without any power supply, due to the aligned magnetic domains within its crystal structure. An electromagnet generates a magnetic field only when electrical current flows through its coil — the field disappears when the current stops. Permanent magnets offer the advantage of zero operating power consumption, while electromagnets offer controllable field strength and on/off capability.

Do permanent magnets lose their magnetism over time? ▼

High-quality sintered NdFeB magnets lose less than 1% of their flux over 10 years at room temperature under normal conditions. Magnetism loss accelerates significantly when magnets are exposed to temperatures above their rated Curie temperature, strong opposing fields, or severe mechanical shock. Properly specified magnets in a controlled application retain near-full magnetization for decades.

What is the strongest type of permanent magnet? ▼

Neodymium (NdFeB) magnets are the strongest commercially available permanent magnets, with energy products (BH_max) ranging from 26 to 52 MGOe. They far exceed Alnico (~5–12 MGOe) and ferrite (~1–5 MGOe). Samarium Cobalt (SmCo) is comparable in strength (~16–32 MGOe) but excels at elevated temperatures where NdFeB loses performance.

Can permanent magnets be re-magnetized once they lose strength? ▼

Yes — if a magnet has partially demagnetized but has not been physically damaged or oxidized, it can be re-magnetized by applying a strong enough external pulsed field (typically >3 Tesla for NdFeB). Radial Magnets offers re-magnetization services. However, if the loss was caused by operating above Tc or by corrosion, re-magnetization will not restore original performance.

Magnet Fundamentals

Key Magnetic Properties Explained

Understand the datasheet values that determine whether a magnet will perform in your application — Br, Hc, BH_max, Tc, and more.

B-H CurveDatasheet InterpretationEngineering Reference

remanence Brcoercivity Hcenergy product BHmaxCurie temperaturemagnetic datasheet

The Six Core Properties on Every Magnet Datasheet

Remanence

B_r

Tesla (T) or Gauss (G)

Coercivity

H_cj

kA/m or kOe

Energy Product

BH_max

kJ/m³ or MGOe

Curie Temp

T_c

°C

Max Op. Temp

T_max

°C

Temp Coeff.

α, β

%/°C

Remanence (B_r) — The "Strength" Number

Remanence is the magnetic flux density remaining in a fully saturated magnet after the external magnetizing field is removed. It represents the maximum flux the magnet can produce in a closed circuit (zero air gap). A higher B_r means more flux is available for a given magnet volume.

B_r = μ₀ · M_r where M_r is the remanent magnetization

For N52 grade NdFeB, B_r ≈ 1.42–1.48 T. For a typical ceramic ferrite, B_r ≈ 0.38–0.40 T — nearly 4× lower, which is why neodymium magnets produce much stronger fields for the same size.

Coercivity (H_cj) — Resistance to Demagnetization

Coercivity measures how strongly the magnet resists being demagnetized by an opposing magnetic field. There are two coercivity values on datasheets:

H_cb (Inductive coercivity): The field required to reduce B to zero in the demagnetization curve. Less commonly used for magnet selection.
H_cj (Intrinsic coercivity): The field required to reduce the intrinsic magnetization M to zero. This is the value that matters for demagnetization resistance — always check H_cj when specifying.

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Temperature warning: H_cj decreases rapidly with temperature for standard NdFeB grades. At 100°C, coercivity may drop 30–40%. If your application runs hot, you must specify a higher-coercivity grade (H, SH, UH, EH, or AH) — not just the same grade as your room-temperature calculation.

Maximum Energy Product (BH_max) — The Figure of Merit

BH_max is the most commonly cited single-number measure of a magnet's "strength." It represents the maximum product of B and H on the demagnetization curve and describes how much magnetic energy can be stored per unit volume. The grade number in NdFeB naming (e.g., N42, N52) directly encodes this value in MGOe.

BH_max [MGOe] ≈ Grade number (e.g., N42 → 42 MGOe ≈ 334 kJ/m³)

Curie Temperature (T_c) and Maximum Operating Temperature

The Curie temperature is the point at which thermal energy overcomes magnetic order and the material becomes paramagnetic (loses all permanent magnetism). For NdFeB, T_c ≈ 310–320°C.

However, the maximum operating temperature (T_max) is substantially lower because irreversible flux loss begins well below T_c. For standard N-grade NdFeB, T_max is just 80°C. Higher-coercivity grades extend this:

Grade Suffix	Max Operating Temp	Example Grades
(none) N	80°C	N35, N42, N52
M	100°C	N35M, N42M
H	120°C	N35H, N42H
SH	150°C	N35SH, N42SH
UH	180°C	N35UH, N38UH
EH	200°C	N35EH, N38EH
AH	230°C	N35AH

Temperature Coefficients (α and β)

Magnetic properties change reversibly with temperature according to temperature coefficients. For NdFeB:

α (alpha) — Temperature coefficient of B_r: Typically –0.11 to –0.13 %/°C. B_r drops ~11% for every 100°C rise.
β (beta) — Temperature coefficient of H_cj: Typically –0.55 to –0.65 %/°C. Coercivity drops ~55% for every 100°C rise for standard grades.

These reversible losses recover when the magnet cools back down. Irreversible losses — caused by operating above T_max — do not recover without re-magnetization.

What does the "N" in N42 or N52 mean? ▼

The "N" stands for Neodymium (NdFeB). The number that follows (35, 42, 52, etc.) indicates the maximum energy product in MGOe. N52 magnets have BHmax ≈ 52 MGOe, making them among the strongest commercially available magnets. Higher numbers mean stronger magnets in the same volume.

What is the difference between Hcb and Hcj? ▼

H_cb (inductive coercivity) is the reverse field that reduces the measured flux density B to zero. H_cj (intrinsic coercivity) is the reverse field that reduces the intrinsic magnetization M to zero. H_cj is always higher than H_cb and is the more critical value for predicting demagnetization risk — especially at elevated temperatures. Always use H_cj in load-line calculations.

Magnet Materials

Neodymium (NdFeB) Magnets: The Complete Guide

The world's strongest permanent magnet material — covering composition, manufacturing, grades, temperature behavior, and why NdFeB dominates modern engineering.

NdFeBRare EarthSintered & BondedN35–N52

neodymium magnetNdFeBrare earth magnetsintered neodymiummagnet grades

What Is a Neodymium Magnet?

Neodymium magnets — officially designated Nd₂Fe₁₄B — are a family of rare-earth permanent magnets first developed independently by General Motors and Sumitomo Special Metals in 1984. They are the strongest type of permanent magnet commercially available today, with energy products up to 52 MGOe — more than 10× that of ceramic ferrite magnets.

The alloy consists primarily of neodymium (Nd), iron (Fe), and boron (B) in a tetragonal crystal structure that creates extremely high magnetocrystalline anisotropy. Small additions of dysprosium (Dy) or terbium (Tb) are used in high-temperature grades to boost coercivity.

Sintered vs. Bonded NdFeB

Property	Sintered NdFeB	Bonded NdFeB
BH_max	26–52 MGOe	5–12 MGOe
Density	~7.5 g/cm³	~5.5–6.2 g/cm³
Shape flexibility	Limited (machined)	High (molded)
Tolerances	±0.05–0.1mm	±0.05–0.2mm (mold)
Corrosion resistance	Requires coating	Better (binder protects)
Cost (volume)	Lower at scale	Higher per kg
Best for	Maximum performance	Complex geometries, thin walls

Grade System Overview

NdFeB grades follow the pattern [N][energy product][temperature suffix]. The energy product number runs from 28 to 55 MGOe; the temperature suffix indicates the operating temperature range. Common grades stocked by Radial Magnets:

N35N38N40N42N45N48N50N52 N35MN38MN40MN42M N35HN38HN40HN42H N35SHN38SHN42SH N35UHN38UH N35EHN38EH N35AH

Strengths and Limitations

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Why engineers choose NdFeB: Highest energy density of any permanent magnet material; enables smaller, lighter motors and assemblies; excellent room-temperature performance; widely available in a full range of grades and shapes; cost-effective at volume.

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Key limitations to plan for: (1) Susceptible to corrosion — always specify a protective coating. (2) Brittle — cannot be drilled or stamped after sintering; must be machined with diamond tools. (3) Temperature sensitive — standard grades rated only to 80°C; specify H/SH/UH/EH grades for higher temperatures. (4) Strong attraction forces — significant safety hazard when handling large magnets.

China's Role in the NdFeB Supply Chain

China produces approximately 85–90% of the world's NdFeB magnets and controls a dominant share of global rare earth mining and processing capacity. This concentration creates procurement risk for manufacturers dependent on a single source region.

Radial Magnets works directly with qualified magnet manufacturers and maintains buffer inventory to mitigate supply disruption risk. For critical applications, we recommend reviewing our Rare Earth Supply Chain guide for strategic stocking considerations.

Are neodymium magnets safe to use near electronics? ▼

Neodymium magnets can damage magnetic storage media (hard drives, credit cards, old-format tape) and may affect sensitive instruments. They do not harm solid-state electronics like SSDs, flash drives, or most modern circuit boards. However, strong fields can induce currents in nearby conductors, so minimum clearances should always be confirmed in high-precision electronic environments. Pacemakers and other implantable medical devices require strict minimum distances — consult your device manufacturer.

What is the difference between N42 and N52 neodymium magnets? ▼

N42 has BH_max ≈ 42 MGOe and B_r ≈ 1.28–1.32 T. N52 has BH_max ≈ 52 MGOe and B_r ≈ 1.42–1.48 T. For the same magnet geometry, N52 produces roughly 15–20% more surface field than N42. The tradeoff: N52 is more expensive, slightly more brittle, and has lower H_cj — making it more susceptible to demagnetization in demanding applications. For most industrial designs, N42 or N45 offer the best balance of performance, cost, and robustness.

Can neodymium magnets be used outdoors or in humid environments? ▼

Bare NdFeB corrodes rapidly in humid or wet environments — it will rust within days when exposed to moisture. A properly applied protective coating is essential for any outdoor or high-humidity application. Nickel-copper-nickel triple-layer plating provides good general-purpose protection. For saltwater, chemical, or extreme humidity environments, epoxy or Parylene coatings offer superior resistance. See our Coating Types Compared guide for detailed selection guidance.

Magnet Materials

Permanent Magnet Material Comparison

Side-by-side comparison of NdFeB, SmCo, Alnico, and Ferrite across every major engineering and procurement criterion.

NdFeB vs SmCoAlnicoFerriteMaterial Selection

magnet material comparisonNdFeB vs ferriteSmCo temperaturemagnet selection guide

At-a-Glance Performance Table

Property	NdFeB (Sintered)	SmCo	Alnico	Ceramic Ferrite
B_r (T)	1.0 – 1.48	0.85 – 1.15	0.6 – 1.35	0.20 – 0.43
H_cj (kA/m)	876 – 2,400	600 – 2,000	40 – 160	150 – 400
BH_max (MGOe)	26 – 52	16 – 32	1.5 – 11	1.0 – 5.0
T_max (°C)	80 – 230	250 – 350	450 – 550	250 – 300
T_c (°C)	310 – 320	700 – 800	800 – 860	450 – 460
Corrosion resistance	Poor (needs coat)	Good	Excellent	Excellent
Relative cost	Medium–High	Very High	Medium	Very Low
Machinability	Poor (brittle)	Poor (brittle)	Good (castable)	Poor (brittle)
Density (g/cm³)	7.4 – 7.6	8.2 – 8.4	6.9 – 7.3	4.8 – 5.1
Primary supply risk	High (Nd, Dy)	Very High (Co, Sm)	Low–Medium	Very Low

When to Choose Each Material

Choose NdFeB when…

Maximum energy density is required (smallest possible magnet for the job)
Operating temperature stays below 80°C (or up to 230°C with high-coercivity grades)
Cost efficiency matters at moderate-to-high volumes
A protective coating can be applied and maintained

Choose SmCo when…

Operating temperatures exceed 200°C
High corrosion resistance is needed without a coating
The application is in aerospace, defense, or downhole oil & gas
Cobalt supply risk and cost premium are acceptable

Choose Alnico when…

Extremely high temperature stability is required (>450°C)
The magnet must be cast into a complex shape
Low coercivity is acceptable (Alnico demagnetizes easily — it must be shunted when disassembled)
Applications in musical instrument pickups, instruments, and meters

Choose Ceramic Ferrite when…

Cost is the primary driver and performance requirements are modest
Large volume and bulk weight are acceptable
Inherent corrosion resistance is needed without coating
Applications in refrigerator magnets, loudspeakers, DC motors, and magnetic separators

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Radial Magnets specializes in NdFeB (sintered and bonded) for the widest selection of grades, shapes, and coatings. We also source SmCo for temperature-critical applications. Contact us for a material recommendation specific to your operating conditions.

Is SmCo or NdFeB better for a motor? ▼

For most electric motors operating below 150°C, sintered NdFeB (H or SH grade) is the preferred choice — it offers higher energy product at lower cost than SmCo. SmCo becomes the better choice for motors in high-temperature environments (e.g., traction motors in extreme climates, motors embedded in hot machinery), space applications, or where corrosion resistance is critical and a coating cannot be reliably maintained.

Can I replace a ferrite magnet with a neodymium magnet? ▼

Yes, and it is a common upgrade path — but it requires careful re-engineering. NdFeB is 5–10× stronger than ferrite in the same volume, so a direct drop-in replacement will produce a significantly stronger field and may overload sensors, springs, or latching mechanisms. Typically, the magnet must be reduced in size to match the original field specification. A load-line analysis of the original circuit is recommended before substituting materials.

Coatings & Protection

Magnet Coating Types Compared

A complete guide to nickel, zinc, epoxy, phosphate, gold, and Parylene coatings — including salt spray ratings, thickness, and the right choice for your environment.

Corrosion ProtectionNi-Cu-NiEpoxyParylene

neodymium magnet coatingnickel plating magnetepoxy coated magnetParylene NdFeBsalt spray rating

Why Coatings Are Critical for NdFeB Magnets

Sintered neodymium magnets are composed of Nd₂Fe₁₄B grains bound by a neodymium-rich intergranular phase. This Nd-rich phase is highly reactive — in the presence of moisture, oxygen, or salt, it oxidizes preferentially, causing the magnet to swell, crack, and eventually disintegrate. A magnet left uncoated in a humid environment may degrade within days.

Unlike SmCo or ferrite, NdFeB always requires a protective coating for any real-world application. The coating choice should be matched to the environmental exposure, temperature range, dimensional tolerance requirements, and any mating surface considerations (electrical contact, bonding, etc.).

Coating Comparison Table

Coating	Thickness (µm)	Salt Spray (hrs)	Temp Limit	Key Strengths	Limitations
Ni-Cu-Ni (triple)	10–20	24–96	200°C	Most common; good balance of cost, protection, conductivity	Not for saltwater; chips at edges
Zn (Zinc)	5–15	24–72	150°C	Low cost; sacrificial protection	Poor in acidic environments; limited life
Ni + Epoxy	15–30	96–240	120°C	Excellent moisture barrier; good for outdoor use	Slightly larger dimensions; can outgas at high temp
Epoxy only	15–25	72–120	120°C	Good corrosion resistance; non-conductive; smooth surface	Less durable than Ni; UV degrades some formulations
Gold (Au)	0.5–5 over Ni	>200	200°C	Excellent corrosion resistance; biocompatible; conductivity	Very expensive; thin layer over Ni still needed
Parylene C/D	5–25	200–500+	125–150°C	Conformal; uniform; excellent chemical and moisture resistance	Higher cost; not UV resistant; requires vapor deposition
Phosphate + oil	2–5	12–24	200°C	Lowest cost; good paint adhesion primer	Minimal standalone protection; only suitable as primer
PTFE (Teflon)	10–30	120+	260°C	Non-stick; chemical resistance; high temp	Low adhesion; specialized process needed

The Standard: Nickel-Copper-Nickel (Ni-Cu-Ni)

The industry default for NdFeB magnets is a triple-layer electroplated coating: an initial nickel layer, a middle copper layer for adhesion, and an outer nickel layer for hardness. This system provides:

Bright metallic appearance and smooth surface finish
Good wear resistance for assembly handling
Electrical conductivity (useful for some applications, problematic for others — eddy currents)
24–96 hours salt spray per ASTM B117

Ni-Cu-Ni is the right choice for the vast majority of indoor industrial applications where moisture exposure is incidental rather than sustained.

High-Humidity and Outdoor Applications: Epoxy + Nickel

For outdoor installation, marine environments, or applications involving regular water exposure, a combination of Ni-Cu-Ni undercoat plus an epoxy topcoat provides substantially better protection. The epoxy creates a polymer barrier that dramatically slows moisture ingress, extending useful life in humid environments from weeks to years.

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Medical and implantable applications: Specify gold plating (Au) over Ni-Cu-Ni for biocompatibility. Gold is ASTM F86 compliant, corrosion-proof, and accepted for applications where the magnet contacts tissue or body fluids. For fully implantable applications, Parylene C is also widely used due to its conformal, pinhole-free deposition.

Does the coating affect the magnet's field strength? ▼

Coating materials are non-magnetic and add a small amount of non-magnetic material between the magnet surface and the working air gap. For most coatings (10–25 µm), this effect is negligible — less than 0.5% reduction in surface field for typical magnet geometries. For extremely tight air-gap applications where every micron counts, thinner coatings (e.g., thin Parylene or gold) may be specified. Always account for coating thickness in dimensional tolerances during design.

Can a coated magnet be re-coated if the coating is damaged? ▼

Yes — damaged or corroded magnets can be stripped and re-coated if the underlying magnet material is still intact. The magnet must first be demagnetized (to reduce handling risk during stripping), the old coating stripped chemically, the surface inspected for corrosion, and then re-plated or re-coated. If surface corrosion has penetrated into the magnet body, re-coating will not stop further degradation. Contact Radial Magnets to assess whether re-coating or replacement is the better option for your parts.

Engineering & Procurement

NdFeB Temperature Grades Explained

Understanding N, M, H, SH, UH, EH, and AH grade designations — and how to select the right grade for your operating temperature.

Grade SelectionHigh-Temp MagnetsCoercivity

NdFeB gradehigh temperature magnetN42SHmagnet temperature ratingdysprosium magnet

Why Temperature Grade Matters

All NdFeB magnets experience a loss of coercivity (H_cj) as temperature rises. At sufficiently high temperatures, the working point on the demagnetization curve crosses into the irreversible loss region — and the magnet permanently loses flux. This is why the grade suffix is not a minor detail: choosing the wrong grade for a hot application causes field decay over time that no amount of re-magnetizing will prevent without first fixing the root cause.

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The most common specification mistake: Engineers calculate the required BH_max at room temperature and specify the cheapest grade that meets it, ignoring the operating temperature. If the device reaches 120°C internally, an N42 magnet will demagnetize. The correct approach is to perform a load-line analysis at the maximum operating temperature, then select a grade whose H_cj remains above the working field at that temperature.

Grade Reference Table

Suffix	T_max	Typical H_cj (kA/m)	Key Additive	Cost Premium vs N	Use Cases
N (none)	80°C	876–1,114	None	Baseline	Consumer electronics, lab fixtures, room-temp industrial
M	100°C	1,114–1,353	Low Dy/Tb	+10–20%	Automotive sensors, HVAC, moderate-heat industrial
H	120°C	1,353–1,592	Dy or Tb	+20–35%	Motor drives, servo motors, power tools
SH	150°C	1,592–1,990	Higher Dy/Tb	+35–60%	Traction motors, HVAC compressors, industrial motors
UH	180°C	1,990–2,388	High Dy/Tb	+60–90%	High-performance drive motors, generators
EH	200°C	2,388–2,786	Very high Dy/Tb	+90–130%	Military, aerospace, downhole tools
AH	230°C	>2,786	Maximum Dy/Tb	+130%+	Extreme-temperature specialty applications

The Role of Dysprosium and Terbium

Higher-temperature grades achieve their enhanced coercivity by substituting dysprosium (Dy) or terbium (Tb) for some of the neodymium in the Nd₂Fe₁₄B lattice. Both are heavy rare earth elements (HREEs) that dramatically increase magnetocrystalline anisotropy — and therefore H_cj — at the cost of slightly reducing B_r.

This is why high-temperature grades have a trade-off: a given energy product (e.g., 42 MGOe) requires a larger magnet at SH grade than at N grade, because B_r is slightly lower. Supply of Dy and Tb is concentrated in China and subject to significant price volatility.

How to Select the Correct Grade

Determine maximum operating temperature — measure or simulate the magnet temperature at worst-case load and ambient conditions.
Add a 20°C safety margin — always spec to a grade rated at least 20°C above your measured maximum.
Perform load-line analysis — check that the working point at maximum temperature remains above the knee of the demagnetization curve.
Verify with supplier — request full B-H curve data at operating temperature, not just room-temperature datasheet values.

What is irreversible flux loss and how do I avoid it? ▼

Irreversible flux loss occurs when a magnet operates at a temperature where its working point drops below the knee of the B-H demagnetization curve. The domains that reverse to follow the applied field do not return when the temperature drops — the magnet permanently loses a fraction of its magnetization. To avoid it: (1) select a sufficiently high coercivity grade for the operating temperature; (2) ensure the magnetic circuit does not impose a large demagnetizing field (short magnets in long air gaps are at higher risk); (3) test at maximum operating temperature before finalizing the design.

Does a higher grade number always mean a better magnet? ▼

Not necessarily. A higher energy product (N52 vs N35) means more flux for the same volume, which is beneficial when size and weight matter. But N52 has lower H_cj than N35 — it demagnetizes more easily under opposing fields or at elevated temperatures. For applications with large opposing fields, vibration, or moderate heat, a lower-energy-product grade with higher coercivity may actually perform better and last longer. Always evaluate both BH_max and H_cj together for your specific operating conditions.

Engineering & Procurement

How to Specify a Magnet: The RFQ Guide

Everything a supplier needs to quote and manufacture your magnet correctly — a complete checklist for engineers submitting RFQs.

RFQSpecificationEngineeringQuality

magnet RFQcustom magnet specificationmagnet drawinghow to order custom magnets

The Complete Magnet Specification Checklist

A complete magnet specification eliminates ambiguity and ensures the part you receive performs as designed. Missing even one of these parameters can result in incorrect quotes, long revision cycles, or worse — parts that fail in service.

1. Geometry and Dimensions

Shape: Disc, ring, block, arc, cylinder, sphere, or custom
Dimensions with tolerances: All critical dimensions in mm with ± tolerances (e.g., Ø12.5 ±0.05 mm × 3.0 ±0.05 mm)
Drawing: Always provide a dimensioned 2D drawing or 3D model (STEP preferred)
Surface finish: Specify if Ra or flatness is critical for assembly

2. Material and Grade

Material: NdFeB, SmCo, Alnico, or Ferrite
Grade: Specific grade (e.g., N42SH) or minimum property requirements (B_r ≥ X, H_cj ≥ Y, BH_max ≥ Z)
Maximum operating temperature
Sintered or bonded (for NdFeB)

3. Magnetization Direction

Axial (through thickness), diametric, radial, multi-pole, or custom orientation
Mark the north pole face on the drawing
Specify if the magnet should be delivered magnetized or unmagnetized

4. Coating

Coating type (Ni-Cu-Ni, Zn, epoxy, gold, Parylene, etc.)
Thickness range or maximum (important for press fits and assemblies)
Salt spray requirement (hours per ASTM B117)

5. Performance Requirements

Minimum surface gauss or tesla at a specified test point
Flux per pole (for multipole rings)
Magnetic moment (for torque calculations)

6. Quality and Qualification Requirements

Inspection standards (IEC 60404, customer-specific)
PPAP level (for automotive)
Certificate of conformance / material traceability
RoHS / REACH compliance requirements

7. Commercial Information

Annual volume estimate and initial sample quantity
Target lead time
Packaging requirements (tape-and-reel, tray, bulk)
Delivery destination and Incoterms

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Pro tip: If you are still in the design phase and haven't locked dimensions, share your functional requirements instead: "I need a surface field of 2,000 Gauss at 2mm gap in a space envelope of 15mm OD × 5mm tall." Experienced suppliers like Radial Magnets can back-calculate the optimal magnet geometry and grade for your budget.

Common RFQ Mistakes That Delay Your Quote

Mistake	Why It Causes Problems	Fix
No tolerances specified	Supplier defaults to their standard; may not fit your assembly	Specify ± on all critical dimensions
Grade only, no temp	Grade is ambiguous without temperature context	State max operating temperature
No magnetization direction	Default (axial) may not match your circuit design	Mark north face on drawing
"Strongest available"	Not a specification — may drive cost with no benefit	State minimum BH_max or field requirement
No coating thickness range	Oversized coating can cause press-fit failures	Specify max OD after coating if press-fit

What is the minimum order quantity for custom NdFeB magnets? ▼

Minimum order quantities (MOQ) vary by shape and grade. For simple geometries (disc, ring, block) in common grades, prototypes can often be sourced from inventory with no MOQ. For custom shapes requiring new tooling, MOQs typically range from 100–500 pieces for initial samples, scaling to full production runs of 1,000–50,000+ pieces. Radial Magnets can discuss prototype options and bridge inventory programs for customers transitioning from prototype to production volume.

How long does it take to receive custom magnets? ▼

Typical lead times for sintered NdFeB custom parts are 4–8 weeks from confirmed order for standard geometries and grades. Unusual grades, complex shapes, specialized coatings, or PPAP requirements can extend this to 10–14 weeks. Radial Magnets maintains safety stock of the most common grades and can often ship standard shapes (disc, ring, block) from inventory within days. Contact us to discuss your timeline and we will identify the fastest path to delivery.

Ready to request a quote? Our team responds within one business day with a detailed proposal.

Start Your RFQ →

Applications Library

Magnets in Electric Vehicles & Motors

How permanent magnets enable the traction motors, sensors, actuators, and charging systems in modern electric vehicles — and how to specify them correctly.

EV Traction MotorPMSMIPM MotorNdFeB SH/UH

EV motor magnettraction motor NdFeBPMSM permanent magnetelectric vehicle magnet grade

Why Electric Vehicles Depend on Rare Earth Magnets

The dominant motor topology in modern battery electric vehicles is the Interior Permanent Magnet Synchronous Motor (IPMSM), where NdFeB magnets are embedded in the rotor lamination stack. This design achieves the highest power density, efficiency, and torque-to-weight ratio of any motor type — critical for maximizing vehicle range.

A typical passenger EV traction motor contains 1–4 kg of sintered NdFeB, depending on power output. A high-performance vehicle motor (300+ kW) may use 3–5 kg. At global EV production volumes, this creates enormous demand — and significant supply chain pressure — on the rare earth sector.

Key Magnet Requirements for EV Traction Motors

Parameter	Typical Requirement	Why It Matters
Temperature grade	SH or UH (150–180°C)	Rotor temps spike under high-load cycles
BH_max	38–45 MGOe	High energy density = smaller, lighter rotor
H_cj @ T_max	>1,500 kA/m	Must resist stator demagnetizing field at peak torque
Shape	Arc segments / flat bars	Embedded in rotor slots; must fit tight geometry
Coating	Epoxy or Parylene	Rotor must tolerate centrifugal force + coolant exposure
Tolerance	±0.05 mm or tighter	Rotor balance and assembly precision
PPAP	Level 3 typical	Automotive supply chain requirement

Magnet Configurations in EV Rotors

Surface-Mounted Permanent Magnet (SPM)

Magnets are bonded to the outer surface of the rotor core. Simpler design but limited to moderate speeds due to centrifugal force on the magnet retainer. More common in lower-speed applications like hub motors and some commercial vehicles.

Interior Permanent Magnet (IPM)

Magnets are embedded in slots cut into the rotor lamination stack. The steel surrounding the magnets contains them against centrifugal force — enabling very high rotor speeds (>15,000 RPM). The dominant topology in passenger EV traction motors (used by Tesla, BMW, GM Ultium, and others).

Spoke / V-Type / Delta Arrangements

Advanced IPM rotors arrange magnets in spoke, V, or delta patterns to concentrate flux and further boost torque density. These require precision-ground flat bar or custom-profile magnets and very tight positional tolerances.

ℹ️

Radial Magnets supplies arc segment and flat bar NdFeB magnets for motor rotor assemblies in grades N38SH through N42UH. We support PPAP Level 3 and can provide MSA studies, SPC data, and material traceability to China-based mills. Contact us for a motor magnet RFQ →

Other Magnet Uses in an EV

Beyond the traction motor, a modern electric vehicle contains magnets in dozens of subsystems:

Transmission sensors: Position and speed sensors using disc or ring magnets for commutation feedback
Steering: Electric power steering (EPS) motor — typically a PMSM with arc segment NdFeB
Braking: Regenerative braking generator magnets; ABS speed sensors
HVAC: Compressor motor (scroll compressor driven by 3-phase PMSM)
Charging: OBC and DC-DC converter transformers using soft magnetic cores
Latches and closures: Door, frunk, and charge port latches using disc or block holding magnets
Speakers: High-output cabin audio systems using NdFeB speaker drivers

Why are NdFeB magnets used instead of ferrite in EV motors? ▼

NdFeB magnets deliver 10–15× the energy density of ferrite, enabling dramatically smaller and lighter traction motors. For a given torque output, an NdFeB motor can weigh 40–60% less than an equivalent ferrite design. This weight saving directly improves vehicle range. The higher cost of NdFeB is more than offset by the system-level benefits: smaller motor, smaller inverter, less structural support, and more range from the same battery pack.

What happens if the rotor magnets in an EV motor partially demagnetize? ▼

Partial demagnetization reduces motor torque constant (Kt) and back-EMF constant (Ke), reducing peak torque and efficiency. In some cases, asymmetric demagnetization across poles introduces torque ripple and vibration. The motor control system may compensate initially, but the drivetrain gradually becomes less responsive and less efficient. Severe or complete demagnetization requires motor rebuild. This is why proper grade selection — especially sufficient H_cj at operating temperature — is critical in EV motor design.

Engineering & Procurement

Magnet Safety & Handling Guidelines

Permanent magnets — especially large neodymium magnets — are genuinely dangerous if mishandled. This guide covers safe handling, storage, shipping, and facility precautions.

SafetyHandlingOSHAShipping

neodymium magnet safetymagnet handlingstrong magnet dangermagnet shipping regulations

⚠️

Serious injury risk: Neodymium magnets above approximately 1" (25mm) in diameter can attract to each other or to steel with enough force to crush fingers, break bones, and chip the magnets violently. Large magnets (3"+ diameter) can kill. Never place any part of your body between two large magnets or between a magnet and a steel surface.

Personal Safety Rules

Always wear leather gloves when handling magnets larger than 20mm in any dimension
Never allow two large magnets to come together freely — bring them together slowly and under control, with a non-magnetic spacer
Keep magnets away from pacemakers and implantable devices — maintain at least 12" (30cm) from any person with a cardiac device
Wear safety glasses — magnets can chip and shatter when they collide at high speed
Never machine or drill magnetized parts — magnetic swarf is a fire and inhalation hazard; machine only unmagnetized blanks
Neodymium powder and swarf are flammable — use proper containment and do not use standard fire extinguishers on burning NdFeB

Storage Requirements

Store in cool, dry conditions — humidity accelerates corrosion even on coated magnets
Keep magnets separated from ferrous tools, fixtures, and components; attraction forces across storage containers can exceed the container's structural strength
Use interleaving spacers (wood, cardboard, plastic) to prevent magnets from attracting across shelves
Maintain minimum 1 meter (3 feet) clearance from magnetic storage media, CRT displays, and precision instruments
Label storage areas with magnetic field warning signs per ANSI Z535 standards

Shipping Regulations

Magnetized products that produce a magnetic field of 0.00525 Gauss or more at 7 feet (2.1m) from the package surface are classified as magnetized material under IATA Dangerous Goods Regulations (Section 2.3.5.9) and ICAO technical instructions. Shipments that exceed this threshold require:

Magnetic shielding (mu-metal or steel enclosure around the package)
IATA Class 9 dangerous goods declaration
Compass deviation testing per IATA standards
Carrier pre-approval for air shipment

Radial Magnets handles all IATA/ICAO documentation and proper magnetic shielding for international and domestic air shipments. Ground shipping by UPS/FedEx has no magnetic field threshold but still requires proper packaging to prevent magnets from moving and attracting to vehicle structures.

Do neodymium magnets affect credit cards and phones? ▼

Neodymium magnets can permanently erase magnetic stripe credit cards, hotel key cards, and transit cards. The magnetic stripe on these cards is easily erased by fields that are completely harmless to humans. Modern smartphones with flash storage (SSD) are not harmed by magnet exposure, but a strong magnet placed over a phone's wireless charging coil area or compass sensor may temporarily confuse the compass or disrupt NFC. Always keep strong magnets away from all magnetic stripe cards.

What should I do if a magnet chips or breaks? ▼

Do not handle chipped or broken NdFeB magnets without gloves and eye protection — edges are razor-sharp. Fine magnetic dust from a break is flammable and an inhalation hazard — clean up with a damp cloth (not a dry brush or vacuum that could spread dust into the air). Dispose of magnet fragments as you would any sharp metallic waste. Never attempt to glue a broken magnet back together while it is magnetized — the pieces will attract violently and are uncontrollable.

Engineering & Procurement

Rare Earth Supply Chain & Sourcing Strategy

Understanding the geopolitical, logistical, and procurement risks in the NdFeB supply chain — and how to build resilience into your sourcing program.

Supply ChainRare EarthChina RiskStrategic Stocking

rare earth magnet supply chainneodymium supply riskmagnet shortagestrategic sourcing magnets

The Geographic Concentration Problem

China dominates every stage of the NdFeB supply chain: rare earth mining (~60–70% of global output), separation and refining (~85–90%), magnet alloy production, and finished magnet manufacturing (~85–90%). This concentration means that tariff changes, export controls, environmental regulations, or geopolitical events in China can disrupt global magnet supply with minimal warning.

The 2010 rare earth crisis — in which China briefly restricted rare earth exports, causing neodymium prices to spike by more than 600% in 12 months — demonstrated how quickly supply disruptions can cascade into production shutdowns for downstream manufacturers. The lesson: treating magnets as a commodity purchased on spot pricing without safety stock is a significant operational risk.

Key Volatility Drivers to Monitor

Chinese export quotas and tariffs: Periodically adjusted; sudden restriction events are not uncommon
Heavy rare earth (Dy, Tb) supply: Dysprosium and Terbium are geographically concentrated even within China's producing regions; supply is tighter than Nd
Energy costs: Magnet production is energy-intensive; electricity price increases in China translate to finished magnet prices
Environmental compliance: Periodic crackdowns on rare earth mining and processing have caused multi-week production shutdowns
EV demand growth: Rapidly rising demand from the EV sector tightens available supply for all other magnet users
Ocean freight and port congestion: 4–6 week transit times from China mean lead times extend quickly during shipping disruptions

Strategic Stocking Recommendations

For manufacturers dependent on NdFeB magnets in production, Radial Magnets recommends:

Minimum 90-day safety stock on all critical magnet SKUs — enough to absorb a factory-level supply disruption without production impact
Blanket purchase orders with scheduled releases — secure inventory at current pricing with flexible delivery windows
Dual qualification — qualify at least two magnet suppliers (and two mills if possible) for any single critical part number
Annual spend review — track market pricing quarterly; buy opportunistically during price softness
Grade flexibility where possible — where your design can accept N40SH or N42SH, qualifying both gives sourcing flexibility when one grade tightens

ℹ️

Radial Magnets operates a bonded domestic inventory program for key accounts — allowing you to hold consignment stock or on-call inventory without tying up your own capital. Contact us to discuss a supply agreement tailored to your annual volumes.

Are there non-Chinese sources for NdFeB magnets? ▼

Yes, though with limited scale. Japan (Hitachi Metals, TDK, Shin-Etsu) produces high-quality NdFeB magnets for domestic and export markets, primarily premium grades for automotive and precision applications. European producers (Arnold Magnetic Technologies, Vacuumschmelze) serve specialized markets. The US has recently seen investment in domestic magnet production (MP Materials' magnet facility, Noveon) to support defense supply chain requirements. These non-Chinese sources typically carry a cost premium of 20–50% but offer supply security and compliance advantages.

How do I protect against a sudden magnet price spike? ▼

The most effective protections are: (1) holding sufficient safety stock to ride out short-term spikes without forced buying at peak prices; (2) signing fixed-price contracts for 6–12 months with a trusted distributor; (3) designing in grade flexibility so you can pivot to an available grade during spot shortages; (4) monitoring neodymium oxide spot prices as a leading indicator — finished magnet prices typically follow with a 4–8 week lag. Radial Magnets provides regular market updates to key accounts and can offer pricing protection programs for committed volumes.

Want to discuss a supply agreement or inventory program? We work with manufacturers on customized stocking solutions.

Talk to a Specialist →

Engineering & Procurement

PPAP for Magnets: What to Expect

A guide to Production Part Approval Process requirements as they apply to sintered NdFeB magnets in automotive and precision industrial supply chains.

PPAPAIAGAutomotive QualityPFMEA

PPAP magnetsAIAG PPAP 4th editionmagnet quality automotivemagnet PFMEA control plan

What Is PPAP?

The Production Part Approval Process (PPAP), defined by the Automotive Industry Action Group (AIAG) in its PPAP 4th Edition reference manual, is a standardized supplier qualification and approval process used primarily in the automotive industry. PPAP establishes documented evidence that a supplier's manufacturing process can consistently produce parts that meet all engineering design requirements.

For magnet suppliers, PPAP submission is increasingly required not only for direct automotive OEM tiers but also for Tier 2 and Tier 3 suppliers building sub-assemblies (sensors, actuators, motors) that feed the automotive supply chain.

PPAP Submission Levels

Level	What Is Submitted	When Required
Level 1	Part Submission Warrant (PSW) only	Appearance approval items, non-critical components
Level 2	PSW + limited supporting data	Standard production parts, existing customer relationship
Level 3	PSW + complete supporting documentation	New part, new supplier, design change — most common for magnets
Level 4	PSW + customer-defined requirements	Specified by customer for specific programs
Level 5	PSW + all records reviewed at supplier site	Safety-critical applications, new supplier qualification

Key PPAP Elements for Magnet Parts

Process Flow Diagram

Maps the complete manufacturing sequence from raw material receipt through shipping. For sintered NdFeB magnets, this includes: incoming material inspection → alloy preparation → milling → pressing → sintering → machining → coating → magnetizing → inspection → packaging.

PFMEA (Process Failure Mode and Effects Analysis)

Identifies potential failure modes at each manufacturing step, their effects on the part, and the controls in place to prevent or detect them. For magnets, high-severity failure modes include incorrect grade material, undercured coating, improper magnetization direction, and dimensional non-conformance on critical features.

Control Plan

Documents the inspection and process controls at each stage. For magnets, critical control points typically include: incoming material traceability, dimensional inspection (CMM or optical comparator), magnetic property testing (Gaussmeter or Helmholtz coil), coating adhesion and thickness testing, and final part marking/traceability.

MSA (Measurement System Analysis)

Validates that the inspection gages and measurement systems used are adequate to detect conforming vs. non-conforming parts. For magnets, this includes Gage R&R studies on dimensional inspection and magnetic flux measurement systems.

SPC (Statistical Process Control)

Demonstrates that key processes are in statistical control. Magnets typically require SPC on critical dimensions and magnetic properties (surface gauss or total flux). A minimum Cpk ≥ 1.67 is required for new submissions under AIAG PPAP 4th Edition.

✅

Radial Magnets has completed PPAP Level 3 submissions for multiple automotive programs including ring magnet assemblies for position sensing applications. We maintain PPAP documentation packages and can provide full traceability to China-based mills. Contact us to discuss your program's PPAP timeline and requirements.

What is the typical timeline for a magnet PPAP submission? ▼

A Level 3 PPAP for a new magnet part typically requires 8–16 weeks from part drawing approval to PSW submission, assuming first-time-quality parts from the initial production run. The critical path items are: tooling and first article production (4–8 weeks), dimensional and magnetic measurement system R&R studies (2–3 weeks), SPC data collection over a minimum production run (typically 300 pieces across multiple shifts), and documentation review. Radial Magnets can provide a detailed PPAP timeline based on your part specifics.

Is PPAP required for non-automotive magnet applications? ▼

PPAP is an automotive standard but its underlying methodology is increasingly adopted in medical devices, defense, and industrial automation for critical supplier qualification. Medical device manufacturers often require IQ/OQ/PQ (Installation/Operational/Performance Qualification) documentation that serves a similar purpose. Defense programs may require AS9100 compliance and First Article Inspection (FAI) per AS9102. Radial Magnets can adapt our quality documentation to match your industry's specific supplier qualification requirements.

Reference

Magnetics Glossary A–Z

Definitions for 55+ terms found on magnet datasheets, engineering drawings, and procurement documents — from Alnico to Zero-flux.

DefinitionsDatasheet Terms50+ Terms

magnet glossarymagnetic termsmagnet definitionsBHmax definitioncoercivity definition

A

Air gap: The space between a magnet and the material or device it is interacting with. Increasing the air gap reduces the usable magnetic flux available to the working circuit.
Alnico: A family of permanent magnet alloys composed primarily of Aluminum, Nickel, and Cobalt. Known for high remanence and excellent temperature stability (T_max up to 550°C), but low coercivity.
Anisotropic magnet: A magnet manufactured with a preferred magnetization direction (the "easy axis"), achieved by pressing the magnetic powder in an aligning field. Produces significantly higher energy product than isotropic magnets. Almost all sintered NdFeB magnets are anisotropic.
Axial magnetization: Magnetization direction parallel to the axis (height/thickness) of the magnet — for a disc, the north pole is on one flat face, south pole on the other.

B

B-H Curve (Demagnetization Curve): A graphical representation of the relationship between magnetic flux density (B) and applied magnetic field (H) for a magnet in the second quadrant. Used to determine operating point and demagnetization risk.
BH_max (Maximum Energy Product): The maximum product of B and H on the demagnetization curve, representing the maximum magnetic energy a magnet can store per unit volume. Expressed in MGOe or kJ/m³. The figure of merit for comparing permanent magnet grades.
B_r (Remanence / Remanent Flux Density): The magnetic flux density remaining in a fully saturated magnet after the magnetizing field is reduced to zero, measured in Tesla or Gauss. Represents the maximum flux available in a closed circuit.
Bonded magnet: A magnet manufactured by mixing magnetic powder with a polymer binder and forming by injection molding, compression, or calendering. Offers complex shape capability at the cost of lower energy product vs. sintered grades.

C

Coercivity (H_c): The intensity of the applied magnetic field required to reduce the magnetization of a material to zero after it has been magnetized. See also H_cj and H_cb.
Curie Temperature (T_c): The temperature above which a ferromagnetic material loses all permanent magnetism and becomes paramagnetic. For NdFeB, T_c ≈ 310–320°C.
Coercivity, Intrinsic (H_cj): The applied field required to reduce the intrinsic magnetization M to zero. More meaningful than H_cb for demagnetization resistance assessment, especially at elevated temperatures.

D

Demagnetization: The partial or complete loss of magnetization in a permanent magnet due to exposure to opposing magnetic fields, elevated temperatures, mechanical shock, or radiation.
Diametric magnetization: Magnetization direction across the diameter of a cylindrical magnet, so north and south poles appear on opposite sides of the cylinder's curved surface.
Dysprosium (Dy): A heavy rare earth element added to high-temperature NdFeB grades to increase coercivity (H_cj), enabling higher maximum operating temperatures. Dy reduces B_r slightly and adds significant cost.

E

Easy axis: The preferred crystallographic direction along which a magnetic material can be most easily magnetized. In anisotropic NdFeB, all grains are aligned so their easy axes are parallel, maximizing magnetic performance in that direction.
Energy product: See BH_max.

F

Ferrite magnet: Also called ceramic magnet. Made from iron oxide and strontium or barium carbonate. Very low cost and good corrosion resistance, but energy product is 10–15× lower than NdFeB.
Flux density (B): The total magnetic flux per unit area, measured in Tesla (T) or Gauss (G). 1 T = 10,000 G.
Flux leakage: Magnetic flux that leaves the intended magnetic circuit path and passes through the surrounding air or non-magnetic materials, reducing useful circuit flux.

G

Gauss (G): CGS unit of magnetic flux density. 1 Gauss = 0.0001 Tesla (T). Surface fields of NdFeB magnets are commonly expressed in Gauss.
Grade (magnet): A designation describing the magnetic properties of a magnet alloy, combining a material prefix (N for NdFeB) with energy product value and temperature suffix (e.g., N42SH).

H

H_cb (Inductive coercivity): The reverse applied field required to reduce flux density B to zero on the demagnetization curve. Lower than H_cj.
H_cj (Intrinsic coercivity): See Coercivity, Intrinsic.
Halbach array: A special arrangement of magnets in which the magnetization direction rotates around the array, concentrating flux on one side and nearly canceling it on the other. Used in linear motors, MRI machines, and magnetic levitation systems.
Hard magnet: A magnetic material that is difficult to demagnetize, retaining its magnetization under normal conditions. All permanent magnet materials are "hard" magnets.

I

Irreversible flux loss: Permanent loss of magnetic flux resulting from exposure above the maximum operating temperature or to opposing fields exceeding the magnet's coercivity at that temperature. Cannot be recovered without re-magnetization.
Isotropic magnet: A magnet with no preferred magnetization direction — can be magnetized in any direction after manufacturing. Lower energy product than anisotropic magnets. Common in bonded ferrite and some bonded NdFeB.

K

Knee (of the B-H curve): The inflection point on the demagnetization curve below which B drops sharply as H increases. Operating below the knee results in irreversible demagnetization. High-coercivity grades have a nearly linear demagnetization curve through second quadrant — no knee — providing a large safety margin.

L

Load line: A line drawn on the B-H demagnetization curve representing the operating point of a magnet in its magnetic circuit. The slope of the load line is determined by the permeance coefficient of the circuit (geometry of magnet and air gap).

M

Magnetization: The process of aligning magnetic domains within a material by exposing it to an external magnetic field equal to or greater than the saturation field. For NdFeB, a pulsed field of >3 Tesla is typically required.
Maximum energy product: See BH_max.
MGOe (Mega Gauss Oersteds): CGS unit of maximum energy product BH_max. 1 MGOe ≈ 7.96 kJ/m³.
Multipole magnetization: Magnetization of a single magnet with alternating north and south poles around its circumference or on its face, achieved with a special multi-pole magnetizing fixture. Common in encoder rings and sensor applications.

N

NdFeB (Neodymium Iron Boron): The alloy system Nd₂Fe₁₄B — the basis for the world's strongest permanent magnets. Available sintered or bonded; requires protective coating to prevent corrosion.
Neodymium (Nd): A rare earth element (atomic number 60) that is the primary alloying element in NdFeB magnets, providing the high magnetocrystalline anisotropy responsible for high coercivity.

O

Oersted (Oe): CGS unit of magnetic field strength (H). 1 Oe = 79.577 A/m. Still widely used on magnet datasheets; 1 kOe = 79.577 kA/m.
Operating point: The specific (B, H) coordinate at which a magnet operates within its magnetic circuit, determined by the load line. Stable operating points lie above the knee of the demagnetization curve.

P

Permeance coefficient (PC): Also called the "load line slope" or B/H at the operating point. Determined by magnet geometry and air gap. A higher PC means the magnet is more efficient (less flux leakage); short wide magnets have lower PC than tall thin ones.
PPAP (Production Part Approval Process): AIAG-defined automotive supplier qualification process requiring documented evidence that a manufacturing process can consistently produce conforming parts. See PPAP for Magnets article.

R

Radial magnetization: Magnetization directed radially outward (or inward) from the center axis of a cylindrical or ring magnet. Requires specialized tooling. Used in motor applications requiring a rotating field.
Remanence: See B_r.
Reversible flux loss: Temporary reduction in magnetic output with increasing temperature that fully recovers when the magnet cools back to its original temperature. Described by the temperature coefficient α.

S

Saturation magnetization (M_s): The maximum magnetization a material can achieve when all magnetic domains are aligned. Applying additional field beyond this point produces no further increase in magnetization.
Sintered magnet: A magnet produced by sintering (solid-state diffusion bonding) of pressed magnetic powder at high temperature and vacuum. Produces fully dense magnets with maximum magnetic properties. The dominant process for NdFeB magnets.
SmCo (Samarium Cobalt): A family of rare earth permanent magnets (SmCo₅ or Sm₂Co₁₇) with excellent high-temperature performance (T_max up to 350°C) and intrinsic corrosion resistance, at higher cost than NdFeB.
Surface gauss: The magnetic flux density measured at the surface of a magnet, typically at the center of the pole face. Commonly used as a quality acceptance criterion. Depends on grade, geometry, and air gap at the sensor.

T

T_c: See Curie Temperature.
T_max (Maximum operating temperature): The highest temperature at which a magnet can operate without exceeding its rated irreversible flux loss limit. Set by grade suffix for NdFeB (80°C for N, up to 230°C for AH).
Temperature coefficient (α, β): The percentage change in B_r (α) or H_cj (β) per degree Celsius of temperature change. For NdFeB: α ≈ –0.12 %/°C, β ≈ –0.60 %/°C (grade dependent).
Tesla (T): SI unit of magnetic flux density. 1 Tesla = 10,000 Gauss. Surface fields of the strongest NdFeB magnets approach 1 T.

W

Working point: See Operating point.

Magnet Fundamentals

The Magnetization Process

How permanent magnets acquire their properties — domain alignment physics, production magnetizing fixtures, pulsed field requirements, and post-magnetization handling.

Magnetizing FixturesPulsed FieldSaturationDomain Physics

Why Magnetization Is a Manufacturing Step, Not a Material Property

A freshly sintered NdFeB blank has all the microstructure needed for strong permanent magnetism, but it starts life magnetically neutral. The individual crystalline grains are aligned during pressing, but without an applied external field they produce no net magnetic moment. Magnetization — exposing the part to a controlled impulse field exceeding its coercive force — converts a machined blank into a functional magnet.

This matters for procurement: magnets can be shipped unmagnetized to avoid handling hazards and attract-force shipping restrictions, then magnetized in the end-use assembly fixture. Most custom magnets from Radial Magnets ship fully magnetized unless otherwise specified.

Magnetic Domain Alignment

Inside a ferromagnetic material, atoms with unpaired electrons align their magnetic moments within small regions called magnetic domains. In an unmagnetized piece, domains point in random directions and cancel out. During sintering of NdFeB, an aligning field is applied while the material is still in powder form — crystallographically aligning the easy-axis of each grain so they can all be magnetized in the same direction. After sintering and machining, a magnetizing pulse snaps the moments into alignment along that easy axis.

ℹ️

The easy axis in NdFeB is the c-axis of the tetragonal Nd₂Fe₁₄B crystal. During powder pressing in an aligning field, >95% of grains orient their c-axis within ±10° of the pressing direction. This pre-alignment is why post-press magnetization is efficient — the field doesn't need to rotate grains, only flip moments.

Magnetizing Equipment and Field Requirements

Saturation magnetization of NdFeB requires an applied field of at least 3× the intrinsic coercivity (Hcj). For N-grade at room temperature, Hcj ≈ 10–12 kOe, so a 30–36 kOe impulse field is required. Higher-coercivity grades (UH, EH) need proportionally stronger fixtures.

Magnetizer Type	Peak Field	Typical Use	Notes
Capacitor-discharge (pulsed)	30–80 kOe	Production magnetizing of sintered NdFeB and SmCo	Fast pulse (<10 ms); most common production method
Helmholtz coil (DC)	Up to 10 kOe	Low-Hcj materials; calibration	Cannot saturate high-coercivity NdFeB
Shaped magnetizing fixture	Matches part geometry	Multipole, radial, or custom orientation	Custom-wound copper coils; encodes complex pole patterns
Through-field solenoid	20–50 kOe	Axial magnetization of cylinders/rings	Uniform field; lower capital cost than shaped fixtures

Magnetization Orientations

Axial: Field parallel to the cylinder or disc axis — north and south poles on flat faces.
Diametric: Field perpendicular to the cylinder axis — poles on curved surface.
Radial: Field radiating outward from center — requires custom radial magnetizing fixtures; common for motor arc segments.
Multipole: Multiple alternating poles encoded around a ring or disc using a multi-tooth fixture — used in encoders and sensing applications.

Handling After Magnetization

⚠️

Magnetized NdFeB parts exert strong attract forces even at small sizes. Two N52 disc magnets 1" × ¼" will snap together at 3–4" range and can pinch skin severely. Use spacers, wooden fixtures, and padded gloves when handling magnetized production magnets.

Store magnetized magnets separated by keeper plates or foam spacers to prevent snap-together damage and cracking.
Keep magnetized magnets >12" from hard drives, pacemakers, credit card strips, and other field-sensitive devices.
Machining after magnetization is not recommended — sparks from NdFeB grinding can ignite in the presence of a strong flux field.

Frequently Asked Questions

Can I magnetize NdFeB magnets myself in the field?

Not practically for sintered NdFeB. The 30+ kOe fields required for saturation are only achievable with industrial capacitor-discharge magnetizers. For parts that will be magnetized after assembly to avoid handling hazards, discuss fixture design requirements with your magnet supplier at the RFQ stage.

Does the magnetizing step change the grade or coercivity?

No. Grade and coercivity are fixed by composition and sintering. Magnetization only aligns existing moments — it doesn't change intrinsic properties. However, insufficient magnetizing field leaves Br below the rated value. Always specify full saturation in your quality plan.

Magnet Fundamentals

Demagnetization: Causes & Prevention

The four mechanisms that permanently or temporarily reduce magnet strength — and how to engineer against each one.

TemperatureOpposing FieldsB-H Curve KneeFlux Loss

The Four Demagnetization Mechanisms

Mechanism	Cause	Reversible?	Defense
Thermal (reversible)	Temperature rise reduces spin coupling	Yes — flux returns on cooling	Operate below rated max temp; account for temp coefficient
Thermal (irreversible)	Sustained elevated temp causes domain restructuring	No — remagnetization required	Select higher temp grade (H, SH, UH, EH)
Opposing field	External field exceeds knee of B-H curve	Partial — depends on operating point	Keep Hd below knee; use high-Hcj grade
Mechanical shock	Vibration or impact disrupts domain alignment	Partial	Secure mounting; avoid impact; protect with housing
Radiation	High-energy particle flux displaces lattice atoms	No	Shield or use SmCo (more radiation-hard)

Temperature Demagnetization

NdFeB has large temperature coefficients: Br decreases at approximately −0.12%/°C and Hcj at approximately −0.6%/°C. These are reversible losses — cool the magnet and full flux returns. The irreversible problem occurs when temperature is sustained long enough for grain boundary phases to restructure or when coercivity can no longer prevent domain reversal.

⚠️

The 80°C Rule for N-grade: Standard N-grade NdFeB is rated to 80°C maximum operating temperature. Even brief spikes above this can cause irreversible flux loss — particularly in thin cross-sections where the magnet's own demagnetizing field compounds the thermal effect. Select M, H, SH, UH, or EH grades for elevated temperature environments.

Operating Point and the B-H Curve Knee

The single most important demagnetization analysis is identifying the operating point on the B-H demagnetization curve at maximum temperature, and ensuring it stays above the knee. Below the knee, any additional reverse field causes catastrophic irreversible loss.

High Pc (thick magnet, short air gap) → operating point high on curve, far from knee → safe
Low Pc (thin magnet, large air gap, strong opposing field) → risk of demagnetization near or below knee

NdFeB grades with higher suffix letters (H, SH, UH) have higher Hcj, shifting the knee further left — allowing operation in stronger opposing fields without irreversible loss. This is the primary reason to specify a higher grade even when temperature itself isn't the only concern.

Measuring Flux Loss

Post-demagnetization flux measurement is performed with a fluxmeter and Helmholtz coil (for total flux) or a Gaussmeter at a defined measurement point. A control plan should specify measurement frequency and acceptance limits (typically ±5% of nominal flux).

Frequently Asked Questions

Will dropping a magnet cause it to lose strength?

For sintered NdFeB, a single drop on a hard floor is unlikely to cause measurable demagnetization, but may chip or crack the magnet (NdFeB is brittle). Alnico magnets are more susceptible to shock demagnetization and should be stored with keeper plates. If flux verification is critical, measure after any drop event.

What is the Curie temperature and does it matter in practice?

The Curie temperature is the point at which ferromagnetic ordering completely collapses. For NdFeB, Tc ≈ 312°C. Irreversible demagnetization occurs far below Tc — at the rated maximum operating temperature of the grade. Never approach Tc in normal operation; the grade ratings (80°C for N through 230°C for AH) are the practical limits.

Magnet Materials

Samarium Cobalt (SmCo) Magnets

Two alloy systems, their properties, grades, and the applications where SmCo outperforms NdFeB on temperature, stability, and corrosion resistance.

SmCo5 (1:5)Sm₂Co₁₇ (2:17)High TemperatureNo Coating Required

Two Alloy Systems

Property	SmCo5 (1:5)	Sm₂Co₁₇ (2:17)
Typical BHmax (MGOe)	16–25	26–32
Br (kG)	8.5–10.5	10.5–12.5
Hcj (kOe)	18–30+	18–30+
Max operating temp (°C)	250	350
Curie temp (°C)	720	820
Br temp coefficient (%/°C)	−0.04	−0.03
Corrosion resistance	Excellent — no coating required	Excellent — no coating required
Relative cost vs. NdFeB	3–5×	4–7×

Why SmCo Instead of NdFeB?

Operating temperature >150°C: NdFeB EH-grade tops at ~200°C; Sm₂Co₁₇ reaches 350°C with far smaller flux loss per degree.
Temperature stability in precision instruments: SmCo's Br temp coefficient (−0.03%/°C) is 4× more stable than NdFeB's — critical for sensors, meters, and traveling-wave tubes.
Corrosive environments without coating: SmCo does not require a protective coating in most industrial and aerospace environments.
Radiation hardness: SmCo is preferred for space and nuclear applications where radiation degrades NdFeB more rapidly.
Long-term stability: SmCo shows minimal aging flux loss over decades — important for reference magnets and instruments expected to operate without recalibration for 10–20 years.

SmCo Grade Table

Grade	BHmax (MGOe)	Br (kG)	Hcb (kOe)	Hcj (kOe)	Max Temp (°C)
SmCo 18	18	9.3	8.5	18	250
SmCo 22	22	10.2	9.3	22	250
SmCo 26	26	11.3	10.0	26	350
SmCo 28	28	11.8	10.5	28	350
SmCo 30	30	12.2	11.0	30	350
SmCo 32	32	12.5	11.5	32	350

Brittleness and Machining

SmCo is extremely brittle — more so than NdFeB. It chips and cracks easily. All precision grinding should be performed wet with diamond wheels before magnetization. Avoid mechanical clamping that applies point loads — use conformal fixtures.

Need SmCo for a high-temperature or precision application? Radial Magnets supplies Sm₂Co₁₇ and SmCo5 in disc, ring, block, and custom shapes.

Request SmCo Quote

Frequently Asked Questions

Does SmCo need a protective coating?

Generally no — SmCo has excellent intrinsic corrosion resistance. A thin passivation layer is common; in aggressive chemical or salt-spray environments a nickel or epoxy coating may be applied, but it is not required for most industrial uses. This is a key advantage over NdFeB, which corrodes rapidly without plating.

What is the lead time for SmCo vs. NdFeB?

SmCo has a longer production lead time than NdFeB (typically 8–14 weeks for custom shapes vs. 4–8 weeks for NdFeB) due to lower production volumes and more complex sintering. Discuss lead time requirements early in your design process. Radial Magnets maintains buffer stock on common SmCo grades.

Magnet Materials

Alnico Magnets

The original high-performance permanent magnet alloy — and where it still excels despite lower energy density than rare earths.

Alnico 5Alnico 8High TempLow Coercivity

Composition and Structure

Alnico is an alloy of Aluminum, Nickel, and Cobalt, with iron as the base and small amounts of copper and titanium. Produced either by casting or sintering — cast Alnico achieves higher magnetic properties.

Alnico Grade Comparison

Grade	BHmax (MGOe)	Br (kG)	Hcb (Oe)	Max Temp (°C)	Key Characteristic
Alnico 2	1.6	7.5	560	450	Cast; good for sensing applications
Alnico 5	5.5	12.5	640	540	Most common; high Br, low Hcb
Alnico 5DG	7.5	13.5	700	540	Grain-oriented; highest energy product in Alnico
Alnico 8	5.3	8.2	1650	550	Higher coercivity; better for opposing-field environments
Alnico 9	9.0	10.6	1500	550	Grain-oriented; highest overall Alnico performance

Strengths of Alnico

Highest operating temperature: Alnico operates up to 450–550°C — far exceeding SmCo (350°C) or NdFeB (230°C).
No rare earth content: Insulated from rare earth supply chain price volatility.
Stability over decades: Properly stabilized Alnico shows virtually no aging flux loss over 20–50 years.

Limitations: Low Coercivity

Alnico's critical limitation is very low coercivity — Hcb of 640–1650 Oe vs. 10,000–30,000+ Oe for NdFeB or SmCo. Alnico magnets are easily demagnetized by opposing fields, mechanical shock, or improper storage without keeper plates.

⚠️

Always use keeper plates when storing Alnico magnets. A keeper plate (soft iron bar across the poles) provides a closed flux path, stabilizing the domain structure. Alnico stored without keepers can lose 5–15% flux over months through self-demagnetization.

Frequently Asked Questions

Why do guitar pickups use Alnico instead of NdFeB?

Alnico 2 and 5 have a lower, "softer" flux density than NdFeB, which affects string vibration damping and frequency response in ways players prefer for certain styles. Alnico 5 is the modern PAF humbucking standard; Alnico 2 is considered "vintage." The tonal difference is real and measurable — not just marketing.

Magnet Materials

Ceramic / Ferrite Magnets

The world's most widely produced permanent magnet — properties, grades, unique temperature behavior, and when ferrite is the right engineering choice.

Strontium FerriteY-Series GradesNo Coating NeededLow Cost

What Is a Ceramic Magnet?

Ceramic (ferrite) magnets are made from iron oxide combined with strontium carbonate or barium carbonate. Strontium ferrite is the dominant commercial type. Raw materials are abundant, inexpensive, and entirely free of rare earth elements — making ferrite immune to rare earth supply chain volatility. Ferrite does not corrode and requires no protective coating.

Ferrite Grade Properties

Grade	BHmax (MGOe)	Br (kG)	Hcb (Oe)	Hcj (Oe)	Notes
Y25	1.6–2.0	3.7–4.1	2380–2780	2700–3100	General purpose; isotropic option
Y30	2.6–3.0	3.9–4.1	2700–3100	3100–3600	Standard anisotropic; most common
Y33	3.0–3.3	4.1–4.3	2700–3200	3200–3800	Higher energy product; motors
Y35	3.3–3.8	4.3–4.6	2700–3300	3200–4000	High performance; speakers, motors
Y40	3.8–4.0	4.5–4.8	2800–3400	3500–4500	Premium; highest BHmax for ferrite

Unique Temperature Behavior

Ferrite coercivity (Hcj) increases as temperature decreases — opposite to NdFeB, which loses coercivity rapidly on cooling below room temperature.

ℹ️

Watch out for low-temperature demagnetization: While Br decreases slightly on cooling, Hcj increases. But the net effect on the operating point means ferrite magnets in circuits with strong opposing fields can paradoxically demagnetize at low temperatures. Design for both temperature extremes, not just high temperature.

When to Choose Ferrite

Cost is primary constraint: Ferrite is 10–30× less expensive per unit energy than NdFeB.
No coating required: Outdoor, wet, and chemical environments where NdFeB would corrode are natural fits.
High volume production: Ferrite tooling and production costs are lower; injection-molded bonded ferrite achieves complex shapes economically.

Frequently Asked Questions

Do ceramic magnets rust or corrode?

No. Ferrite magnets are chemically inert iron oxide — already fully oxidized. They do not rust, corrode, or degrade in humid, wet, or outdoor environments, making them naturally suitable for outdoor applications without any coating or treatment.

Shapes & Orientations

Disc & Cylinder Magnets

The most versatile magnet form factor — D/H ratios, field patterns, pull force vs. gap behavior, and application guidance.

AxialD/H RatioPull ForceDiametric

D/H Ratio and Permeance Coefficient

D/H Ratio	Shape	Permeance Pc	Demag Resistance	Typical Use
>5:1	Very thin disc / wafer	Low (~1–2)	Low	Sensor targets, assembly shims
2:1–5:1	Standard disc	Medium (~2–4)	Moderate	General purpose, holding, sensors
~1:1	Puck / coin	Medium-high (~4–6)	Good	Motor magnets, Reed switch actuators
0.5:1–1:1	Short cylinder	High (>6)	Very good	Motor rotors, MRI coils
<0.5:1	Tall cylinder / rod	Very high	Excellent	Loudspeaker motors, push rods

Pull Force vs. Air Gap

Pull force falls off rapidly with air gap. Practical rules for disc magnets:

Rated pull force is measured steel-to-steel contact with no air gap.
At 1 mm air gap, pull force typically drops 30–50% of contact value.
At 3 mm air gap, pull force is often less than 25% of contact value.
At 10 mm, most small disc magnets produce negligible usable force.

ℹ️

Pull force specifications assume the magnet is attracting a large flat steel plate. Pull force to another magnet of the same grade is approximately equal at contact, but force between two small magnets with no back-iron is significantly lower than spec sheet values.

Diametrically Magnetized Discs

Disc magnets can be supplied diametrically magnetized (poles on the curved surface). This is common for angular position sensing — a diametrically magnetized disc rotated above a Hall sensor produces a sinusoidal output proportional to rotation angle — and for BLDC motor feedback.

Need disc or cylinder magnets? Radial Magnets stocks NdFeB disc magnets in N35–N52 grades, multiple coatings, and custom sizes.

Request Disc Magnet Quote

Frequently Asked Questions

Why does my disc magnet pull force seem much lower than the datasheet?

The most common reasons: (1) there is an air gap — even a paint layer reduces force significantly; (2) the steel target is too thin; (3) the target is non-magnetic stainless steel; (4) you are measuring force to another magnet, not to a large flat steel plate. Spec sheet pull force is always measured at direct contact to a large steel plate.

Shapes & Orientations

Ring / Annular Magnets

Design guide for ring magnets — ID/OD/height ratios, magnetization options, encoder and sensor configurations, and motor assembly considerations.

Axial RingRadial RingMultipoleEncoder

Magnetization Options for Ring Magnets

Magnetization	Pole Location	Typical Application	Notes
Axial	North/south on flat faces	Holding magnets, sensor targets, speaker rings	Most common; highest flux on axis
Diametric	Opposite curved OD surface (1 pole pair)	Angular sensing, BLDC feedback	Sinusoidal output when rotated over Hall sensor
Radial (outward)	All north on OD, all south on ID (or reverse)	Loudspeaker gap motors, Halbach arrays	Requires radial magnetizing fixture; higher cost
Multipole (axial)	Multiple N/S pairs on one face	Magnetic encoders, rotary position sensors	Pole count 2–128; match to sensor IC requirements
Multipole (OD)	Multiple N/S pairs around curved surface	Linear encoders, BLDC motors	Pole pitch must match sensor array spacing

Ring Magnets in Encoder Applications

Multipole ring magnets are the sensing element in most incremental and absolute magnetic encoders. Key parameters to specify:

Pole count: Matched to encoder resolution requirement.
Pole pitch uniformity: Angular spacing errors translate to position errors. Specify ±2% or better for precision encoders.
Air gap to sensor: Typically 0.5–1.5 mm; confirm with sensor IC datasheet (peak-to-peak field typically 20–100 mT).

ℹ️

Wall thickness (OD−ID)/2 should be at least 10–15% of OD. Very thin walls are difficult to handle without chipping. Minimum practical wall thickness for sintered NdFeB is approximately 0.5 mm, but 1.5 mm or greater is preferred for handling reliability.

Need ring magnets — standard or multipole? Radial Magnets specializes in custom ring magnet programs including encoder rings and precision sensor targets.

Request Ring Magnet Quote

Frequently Asked Questions

What is the difference between a radially magnetized ring and an axially magnetized ring?

An axially magnetized ring has north on one flat face and south on the other — like a disc with a hole. A radially magnetized ring has north on the entire outer diameter surface and south on the inner diameter (or vice versa), with flux radiating outward through the wall. Radial rings require special fixtures and are more expensive to produce.

Shapes & Orientations

Block & Bar Magnets

Engineering reference for rectangular block magnets — tolerances, magnetization direction options, and applications in IPM rotors, linear actuators, and Halbach arrays.

Thickness MagnetizedIPM RotorToleranceHalbach

Standard Dimensional Tolerances (Sintered NdFeB)

Dimension	Standard	Tight (add-on)	Notes
Length / Width	±0.10 mm	±0.05 mm	Ground dimensions add cost
Thickness	±0.10 mm	±0.05 mm	Critical for motor air gap
Parallelism	0.10 mm	0.05 mm	Important for laminated assemblies
Squareness	±0.5°	±0.2°	Corner geometry for Halbach arrays

IPM Rotor Applications

Block magnets are the primary magnet geometry in Interior Permanent Magnet (IPM) motor rotors. Rectangular NdFeB blocks are inserted into slots in the rotor lamination stack, enabling flux concentration configurations (V-shaped, U-shaped, spoke-type) for high power density.

ℹ️

For IPM rotor production, specify magnet thickness tolerance at ±0.05 mm or tighter. Thickness variation translates directly to air gap variation, affecting torque ripple and back-EMF waveform consistency. Radial Magnets routinely supplies IPM block magnets with PPAP Level 3 documentation for Tier 1 automotive programs.

Halbach Arrays

Alternating-angle block magnet assemblies can form a Halbach array — concentrating flux on one side while nearly canceling it on the other. Used in linear motors, magnetic levitation bearings, and high-efficiency voice coil actuators. Proper angular tolerance (≤±0.2°) is critical for Halbach performance.

Need block magnets for IPM rotors, linear actuators, or custom assemblies?

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Frequently Asked Questions

What is the maximum size for a sintered NdFeB block magnet?

Practical maximum dimensions are approximately 100 mm × 100 mm × 50 mm. Larger sections are difficult to sinter uniformly and risk cracking during cooling. Very large magnet assemblies are typically built from multiple smaller blocks bonded into a housing. Contact Radial Magnets for large block requirements.

Shapes & Orientations

Arc / Segment Magnets

The motor builder's magnet — arc geometry, pole arc angles, parallel vs. radial magnetization, and manufacturing considerations for rotor assemblies.

Pole Arc AngleParallel MagRadial MagSPM Rotor

Pole Arc Ratio

The pole arc ratio is the magnet's subtended angle divided by the pole pitch (360°/number of poles). For an 8-pole motor, pole pitch = 45°. A magnet subtending 40° has a pole arc ratio of 0.89.

Pole Arc Ratio	Back-EMF Waveform	Torque Ripple	Notes
0.65–0.70	Trapezoidal	Higher	BLDC (6-step) drive compatible
0.75–0.85	Approaching sinusoidal	Moderate	General purpose SPM
0.85–0.95	More sinusoidal	Lower	FOC / PMSM drives preferred

Parallel vs. Radial Magnetization

Parallel: All flux lines are parallel — equivalent to magnetizing a block and bending it. Simple to produce; less costly. Back-EMF waveform is slightly trapezoidal.
Radial: Flux lines radiate from the rotor center. Produces more sinusoidal back-EMF and more uniform air gap flux density. Requires custom radial fixture; higher cost but improved motor performance.

ℹ️

Radial Magnets supplies arc segments from N38SH through N42UH for automotive traction motor programs. We support custom pole arc angles, parallel or radial magnetization, and PPAP documentation. For RFQ, provide: IR, OR, arc angle, axial length, grade, coating, and magnetization direction.

Need arc segment magnets for motor or generator assemblies?

Request Arc Magnet Quote

Frequently Asked Questions

What grade should I use for an EV traction motor arc magnet?

EV traction motor arc magnets typically require N38SH to N42UH depending on peak rotor operating temperature. The SH grade (max 150°C) is a common starting point; UH (max 180°C) is specified for applications near the motor temperature limit. Select a grade with at least 20°C margin above your worst-case peak rotor temperature.

Shapes & Orientations

Magnetization Directions Explained

Axial, diametric, radial, multipole — how to specify the correct magnetization orientation for your magnetic circuit and application.

AxialDiametricRadialMultipole

Quick-Reference: Magnetization Directions by Shape

Shape	Direction	Poles Located On	Typical Application
Disc / Ring	Axial	Flat top and bottom faces	Holding, sensor targets, speaker motors
Disc / Ring	Diametric	Opposite curved sides	Rotary angle sensing, BLDC feedback
Ring	Radial (outward)	All N on OD, all S on ID (or reverse)	Loudspeaker gap motors, Halbach rings
Ring / Disc	Multipole axial	Multiple N/S alternating zones on one face	Magnetic encoders, position sensors
Block	Thickness	Two large flat faces	Surface motor magnets, holding pads
Block	Length	Two narrow end faces	Linear actuator flux poles
Arc segment	Parallel (radial dir.)	Concave and convex curved faces	SPM motor rotors (standard)
Arc segment	Radial (true)	Concave and convex (radial flux)	SPM motor rotors (premium)

Diametric Magnetization

For a cylinder or disc, the magnetizing field is applied perpendicular to the axis — across the diameter. When a diametrically magnetized cylinder or disc rotates, a fixed Hall sensor measures a sinusoidal field — making this the standard configuration for rotary angle sensing and BLDC motor Hall feedback.

Multipole Magnetization

A multipole fixture encodes multiple alternating N/S pole pairs into a single magnet face or surface. The number of poles must be specified (always an even number). Pole count options range from 2 to 128+ for encoder rings. The pole pitch must match the sensor IC's optimal field amplitude — consult the sensor datasheet for field strength requirements at your target air gap.

⚠️

Always specify magnetization direction explicitly on your drawing. "Axially magnetized" is ambiguous for a block magnet — specify which dimension (thickness, length, or width). The drawing should show an arrow with the label "Magnetization Direction →".

Frequently Asked Questions

Can I change the magnetization direction of an existing magnet?

Only if the magnet is isotropic (typically bonded or certain Alnico grades). Sintered NdFeB and SmCo are anisotropic — the crystal easy-axis was aligned during powder pressing, and you cannot efficiently magnetize perpendicular to it after sintering. You must order a magnet pressed and sintered with the correct orientation from the start.

Coatings & Protection

Why NdFeB Magnets Need a Coating

The corrosion mechanism in sintered neodymium magnets — and why even small coating breaches lead to rapid magnetic and structural degradation.

Nd-rich PhaseIntergranular CorrosionPinhole ProblemGalvanic

Why NdFeB Corrodes So Readily

Sintered NdFeB is a multiphase material. The main magnetic phase is Nd₂Fe₁₄B, but grain boundaries contain a distinct Nd-rich phase that is:

Highly chemically reactive — neodymium is a very electropositive rare earth
Continuously interconnected throughout the magnet cross-section
An anode relative to the Nd₂Fe₁₄B main phase — galvanic corrosion accelerates the attack

Once moisture reaches the grain boundaries, it attacks the Nd-rich phase, dissolving it and causing individual Nd₂Fe₁₄B grains to separate. The magnet literally crumbles from the inside out.

The Pinhole Problem

A properly applied coating is very effective — but only as good as its most compromised point. Even a single pinhole, scratch, or edge chip can initiate a corrosion cell that propagates laterally under the coating, causing blistering and delamination. This is why edge coverage is critical, and coatings must be matched to the severity of the end-use environment.

⚠️

Do not use abrasive cleaning or mechanical abrading on coated NdFeB magnets. Any surface damage — even superficial scratches — can initiate corrosion in humid environments. If a coating is visibly damaged, recoat or replace the magnet.

The Corrosion's Effect on Magnetic Properties

The corrosion attacks the Nd-rich grain boundary phase, which is critical for maintaining high coercivity. As corrosion progresses, Hcj drops, making the magnet more susceptible to demagnetization. In advanced corrosion, the magnet loses structural integrity and may have only 50–70% of its original flux.

See the full coating comparison →

Coating Types Compared

Frequently Asked Questions

How quickly will an uncoated NdFeB magnet corrode?

In a controlled dry indoor environment (<30% RH), slow surface oxidation may develop over months. At typical indoor humidity (50–60% RH), visible rust appears within days to weeks. In high-humidity or outdoor environments, structural corrosion can begin within 24–48 hours. In saltwater, failure can occur within hours. Never use bare NdFeB where moisture contact is possible.

Coatings & Protection

Selecting the Right Magnet Coating

A practical four-step decision framework — matching coating type to environment, temperature, dimensional constraints, and regulatory requirements.

EnvironmentTemperatureBiocompatibilityDimensional Budget

Step 1 — Define the Operating Environment

Environment	Severity	Minimum Recommendation
Indoor, climate-controlled, dry	Low	Ni-Cu-Ni triple layer
Indoor, possible humidity or condensation	Medium	Ni-Cu-Ni + epoxy topcoat
Outdoor, non-marine	High	Epoxy or Zn phosphate + epoxy
Marine, salt spray, or coastal outdoor	Severe	Parylene C or multi-layer epoxy
Submersed in water	Extreme	Parylene C (conformal) or PTFE
Chemical exposure (solvents, acids)	Special	Parylene C, PTFE, or gold (verify compatibility)

Step 2 — Check Temperature Limits

Coating	Max Continuous Temp (°C)	Notes
Nickel (Ni-Cu-Ni)	200–230	Good for most NdFeB grades
Zinc (Zn)	120	Not suitable for elevated temperature
Epoxy spray/dip	150–180	Verify formulation with supplier
Gold (Au)	300+	Thermally stable; cost limits to critical applications
Parylene C	125 (continuous)	CVD conformal; limited to lower temp ranges
PTFE	260	Excellent thermal stability; non-stick surface

Step 3 — Account for Dimensional Budget

Coating	Typical Thickness (per side)	Notes
Ni-Cu-Ni	10–25 µm	Most precise thickness control
Zinc	8–20 µm	Good thickness control
Epoxy spray	15–30 µm	Moderate control; edges may be thinner
Gold	0.5–3 µm	Very thin; negligible dimensional impact
Parylene C	5–30 µm	Highly uniform conformal coverage
PTFE	15–50 µm	Baked-on; moderate control

Step 4 — Regulatory and Biocompatibility Requirements

Medical implants: Gold or Parylene C — both pass ISO 10993 cytotoxicity. Nickel is a known allergen — not suitable for implantable use.
Food contact: PTFE (FDA-compliant grades) or gold.
RoHS / REACH: All standard coatings are RoHS compliant. Confirm with supplier documentation.

Not sure which coating is right? Radial Magnets can advise and supply magnets with all standard and specialty coatings.

Talk to a Magnet Engineer

Frequently Asked Questions

Why does nickel-plated NdFeB still corrode in some environments?

Nickel-copper-nickel plating is electrodeposited, making pinholes nearly impossible to eliminate completely. In severe environments (marine, salt spray, acidic), moisture finds these pinholes and initiates galvanic corrosion. For severe environments, switch to epoxy or Parylene (more continuous barrier), or specify nickel + epoxy topcoat combination.

Applications Library

Magnets in Medical Devices

NdFeB and SmCo applications in surgical robotics, cochlear implants, drug delivery, hearing aids, and precision positioning — with biocompatibility and regulatory requirements.

ISO 10993Gold / ParyleneMRI SafetyImplantable

Key Application Categories

Application	Magnet Type	Key Requirement	Typical Grade
Cochlear implant (external)	NdFeB disc	Strong hold through scalp; MRI-conditional	N52 or N48H
Cochlear implant (implanted)	NdFeB disc in Ti housing	Biocompatible, hermetic, MRI force/torque limits	N42H with gold + Ti
Surgical robot joint	SmCo or NdFeB	High force density, sterilization-compatible	SmCo 28 or N42SH
Drug delivery capsule	NdFeB micro-disc	Miniature; biocompatible; steerable by external field	N52 with Parylene C
Hearing aid (BTE)	NdFeB micro-disc	Miniature; high BHmax; vibration resistant	N48–N52
MRI gradient coil shim	NdFeB block/disc	Precise calibrated flux; long-term stability	N35–N42, stabilized

Biocompatibility and Coating Requirements

Coating	ISO 10993	Corrosion Resistance	Implantable?
Gold (Au)	Pass	Excellent	Yes (>1 µm thickness)
Parylene C	Pass	Very good (CVD, pinhole-free)	Yes (widely used)
Titanium housing	Pass (fully biocompatible)	Excellent (hermetic)	Yes (gold standard)
Nickel (Ni-Cu-Ni)	Fail (Ni is a sensitizer)	Good	No
Epoxy	Conditional	Good	Limited — not for long-term implant

⚠️

Nickel is not biocompatible. Standard Ni-Cu-Ni plated NdFeB cannot be used in skin-contact or implantable medical devices. Specify gold or Parylene C for medical applications.

MRI Safety Considerations

MRI force/torque: Strong static fields (1.5T or 3T) exert translational force and torque on permanent magnets. Implantable magnets must meet ASTM F2052 and F2213 force/torque limits.
MRI heating: RF pulses induce eddy currents; small magnets typically have minimal heating but must be evaluated per ASTM F2182.
Demagnetization: Rotating gradient fields can partially demagnetize implanted magnets over time, shifting coupling force in cochlear devices.

Medical device magnet procurement requires biocompatible coatings, traceability, and supplier quality documentation. Radial Magnets supports medical programs with lot traceability, CoC, and custom coating specifications.

Contact Medical Device Team

Frequently Asked Questions

Can patients with NdFeB implants get MRI scans?

It depends on the specific device, MRI field strength, and the implant's documented MRI-conditional labeling. Many modern cochlear implant magnets are designed MRI-conditional at 1.5T with a head bandage to restrict movement. Always consult the device's IFU and the implanting surgeon before any MRI examination.

Applications Library

Magnets in Sensors & Encoders

Position sensing, speed detection, and angular measurement — disc, ring, and multipole magnet configurations for Hall-effect and magnetic encoder systems.

Hall EffectAMR / GMRMultipole RingIncremental Encoder

Sensing Technologies and Magnet Requirements

Technology	Measured Quantity	Magnet Type	Key Spec
Hall-effect (latching)	Presence / position (digital)	Disc or block, any grade	Operate / release field at sensor face
Hall-effect (rotary)	Angle (0–360°)	Diametrically magnetized disc or cylinder	Diametric uniformity; air gap 0.5–2 mm
AMR / GMR	Angle, speed (high resolution)	Multipole ring	In-plane field 5–50 mT; field uniformity
Magnetic encoder (incremental)	Position, speed, PPR	Multipole ring (axial or OD)	Pole count, pole pitch uniformity, field amplitude at air gap
Reed switch actuator	Presence (contact closure)	Disc or cylinder	Operate distance; must exceed reed pull-in field at max gap

Multipole Ring Encoders: Resolution Reference

Ring Pole Count	PPR (no interpolation)	PPR (4× interpolation)	Typical Application
8 poles (4 pairs)	4	16	Simple speed sensing, BLDC commutation
32 poles (16 pairs)	16	64	Servo drives, CNC axes
64 poles (32 pairs)	32	128	High-resolution servo
128 poles (64 pairs)	64	256	Precision motion control

Key Application Parameters to Specify

Pole count (always even)
Ring OD, ID, height and grade
Required peak field at air gap distance (from sensor IC datasheet)
Pole pitch uniformity tolerance (typically ±2% for encoder applications)
Magnetization direction (axial face vs. OD surface)

Need encoder rings or sensor magnets? Radial Magnets produces multipole encoder rings from 8 to 128 poles and diametric sensing discs in a range of grades.

Request Sensor Magnet Quote

Frequently Asked Questions

What magnet grade should I use for a temperature-critical Hall sensor?

All NdFeB has Br tempco ≈ −0.12%/°C. If tighter stability is required, consider SmCo — its Br tempco of −0.03%/°C is 4× more stable, at the cost of approximately 5× higher magnet price. For the most stable flux over temperature, specify SmCo 26 or 28.

Applications Library

Magnets in Aerospace & Defense

SmCo and high-grade NdFeB in actuators, gyroscopes, radar systems, and satellite attitude control — with ITAR, AS9100, and military qualification requirements.

SmCoAS9100MIL-PRF-14197ITAR

Why Aerospace Chooses SmCo

Temperature stability: SmCo's Br temp coefficient (−0.03%/°C) is 4× more stable than NdFeB's, critical for −55°C to +200°C+ operational swings.
No coating required: Eliminates a potential failure mode from coating degradation in conformal or vacuum environments.
Radiation hardness: Substantially more radiation-hard than NdFeB — preferred for space particle radiation environments.
Long flight heritage: SmCo has 40+ years of flight heritage in satellites, gyroscopes, and aircraft actuators.

Common Applications and Typical Grades

Application	Magnet Type	Key Requirement
Satellite attitude control (reaction wheels)	SmCo arc segments	Long-term flux stability; radiation hardness; outgassing-free
Gyroscope / INS	SmCo disc or ring	Precision flux calibration; minimal aging; vibration resistance
Radar traveling-wave tube (TWT)	SmCo ring stack	High temp stability; precise focusing field; <0.1% flux variation
Airborne servo actuator	SmCo or NdFeB UH arc/block	High specific power; wide temp range; shock and vibration
UAV motor	NdFeB SH/UH arc	High power density; vibration tolerance; thermal management

Quality Standards

Standard	Scope	Relevance to Magnets
AS9100 Rev D	Aerospace QMS	Supplier quality system requirement for aero suppliers
MIL-PRF-14197	Permanent magnets — military spec	Defines performance requirements and qualification for defense magnets
MIL-STD-810	Environmental engineering	Shock, vibration, temp cycling, humidity test methods
DFARS 252.225-7009	Specialty metals (domestic sourcing)	May require US-origin magnetic materials for certain DoD programs

Aerospace or defense magnet requirement? Radial Magnets has experience supplying SmCo and NdFeB to programs requiring AS9100, MIL-PRF-14197, and traceability documentation.

Contact Aerospace Team

Frequently Asked Questions

Does NdFeB outgas in space (vacuum)?

NdFeB itself has low outgassing, but coatings can contribute. For space applications where contamination of optical surfaces is a concern, bare SmCo (no coating needed, very low outgassing) is preferred over coated NdFeB. If NdFeB is required, specify coating with verified low outgassing per ASTM E595.

Applications Library

Magnets in Industrial Automation

Servo motors, linear actuators, magnetic couplings, and EPM gripper systems — selecting and specifying NdFeB for industrial duty cycles.

Servo MotorLinear MotorMagnetic CouplingEPM Gripper

Key Application Specifications

Application	Grade Typical	Critical Spec	Special Requirement
Servo rotor (SPM)	N38SH – N42SH	Arc angle ±0.5°, IR/OR ±0.05 mm	Adhesive bond testing, PPAP
Servo rotor (IPM)	N35H – N42H	Thickness ±0.05 mm, parallelism 0.05 mm	PPAP, matched sets
Linear motor track	N40H – N45H	Thickness ±0.05 mm, matched sets ±0.02 mm	Thickness sorting, kit packaging
Magnetic coupling	N42 – N48	Flux uniformity across array	Array balancing, flux testing
EPM gripper	N42 (NdFeB) + Alnico 5 or 8	Coercivity matching for EPM switching	Custom array design

Electropermanent Magnet (EPM) Grippers

EPM grippers combine NdFeB and Alnico magnets that can be switched between "on" (holding) and "off" (released) with a brief current pulse. Unlike electromagnets, they consume power only during switching — not continuously while holding. This makes them ideal for collaborative robot grippers and pick-and-place systems handling ferromagnetic parts.

Linear Motor Tracks

Linear motors eliminate mechanical transmission, enabling higher throughput and positioning accuracy. NdFeB block magnets form the stationary magnet track, assembled from individual blocks in alternating polarity bonded to a steel back-plate. Block magnets must have consistent thickness (±0.05 mm) to maintain uniform air gap and minimize thrust ripple.

Industrial automation magnet requirements? Radial Magnets supplies servo motor arcs, linear motor kits, and coupling magnet arrays with full documentation.

Request Industrial Quote

Frequently Asked Questions

What adhesive should I use to bond arc magnets to a steel rotor?

Structural epoxy adhesives (Loctite 648, Permabond ESP110, or similar, rated for 150°C+) are standard for SPM rotor bonding. Key requirements: operating temperature range, shear strength (15–25 MPa minimum), and cure time. Magnets should be cleaned of all oils and chemically etched before bonding. At high rotor speeds (>5,000 rpm), calculate centrifugal stress on the adhesive joint — carbon fiber retention sleeve overwraps are used for very high speed applications.

Interactive Tool

NdFeB Grade Selector

Answer four questions about your application and get an instant grade and coating recommendation with key property data.

Grade RecommendationCoating SelectionInteractive

Answer the questions below — each answer unlocks the next. Your recommendation appears after the final answer.

① What is the maximum operating temperature in your application?

② How important is maximum energy density (BHmax)?

③ What is the operating environment?

④ What are the quality and documentation requirements?

Results

Everything You Need to Know About Magnets

Magnet Fundamentals

Magnet Materials

Shapes & Orientations

Coatings & Protection

Applications Library

Engineering & Procurement

Glossary A–Z

What Is a Permanent Magnet?

Definition: What Makes a Magnet "Permanent"?

The Atomic Origin of Magnetism

Magnetic Domains

Hard vs. Soft Magnetic Materials

How Are Permanent Magnets Manufactured?

Frequently Asked Questions

Related Topics

Key Magnetic Properties Explained

The Six Core Properties on Every Magnet Datasheet

Remanence (Br) — The "Strength" Number

Coercivity (Hcj) — Resistance to Demagnetization

Maximum Energy Product (BHmax) — The Figure of Merit

Curie Temperature (Tc) and Maximum Operating Temperature

Temperature Coefficients (α and β)

Related Topics

Neodymium (NdFeB) Magnets: The Complete Guide

What Is a Neodymium Magnet?

Sintered vs. Bonded NdFeB

Grade System Overview

Strengths and Limitations

China's Role in the NdFeB Supply Chain

Related Topics

Permanent Magnet Material Comparison

At-a-Glance Performance Table

When to Choose Each Material

Choose NdFeB when…

Choose SmCo when…

Choose Alnico when…

Choose Ceramic Ferrite when…

Related Topics

Magnet Coating Types Compared

Why Coatings Are Critical for NdFeB Magnets

Coating Comparison Table

The Standard: Nickel-Copper-Nickel (Ni-Cu-Ni)

High-Humidity and Outdoor Applications: Epoxy + Nickel

Related Topics

NdFeB Temperature Grades Explained

Why Temperature Grade Matters

Grade Reference Table

The Role of Dysprosium and Terbium

How to Select the Correct Grade

Related Topics

How to Specify a Magnet: The RFQ Guide

The Complete Magnet Specification Checklist

1. Geometry and Dimensions

2. Material and Grade

3. Magnetization Direction

4. Coating

5. Performance Requirements

6. Quality and Qualification Requirements

7. Commercial Information

Common RFQ Mistakes That Delay Your Quote

Related Topics

Magnets in Electric Vehicles & Motors

Why Electric Vehicles Depend on Rare Earth Magnets

Key Magnet Requirements for EV Traction Motors

Magnet Configurations in EV Rotors

Surface-Mounted Permanent Magnet (SPM)

Interior Permanent Magnet (IPM)

Spoke / V-Type / Delta Arrangements

Other Magnet Uses in an EV

Related Topics

Magnet Safety & Handling Guidelines

Personal Safety Rules

Storage Requirements

Shipping Regulations

Related Topics

Rare Earth Supply Chain & Sourcing Strategy

The Geographic Concentration Problem

Key Volatility Drivers to Monitor

Remanence (B_r) — The "Strength" Number

Coercivity (H_cj) — Resistance to Demagnetization

Maximum Energy Product (BH_max) — The Figure of Merit

Curie Temperature (T_c) and Maximum Operating Temperature