Radial Magnets, Inc.
Radial Magnets, Inc.we know magnets
Radial Magnets, Inc.
Radial Magnets, Inc.we know magnets
Radial Magnets · Technical Resource
Ferrite is the most-produced permanent magnet on earth by a wide margin, and it is chosen for reasons that have nothing to do with strength. It costs a fraction of anything else per unit of energy, it cannot corrode, it contains no rare earths at all — and it demagnetises when it gets cold, which is the one behaviour that surprises engineers arriving from neodymium.
Ferrite magnets are a sintered ceramic made from iron oxide combined with strontium or barium carbonate. Strontium ferrite dominates commercially; barium ferrite persists in some legacy and specialist applications. The raw materials are abundant, cheap and geographically unremarkable, which is the entire commercial story of the material.
The consequence engineers care about most is that ferrite is already fully oxidised. Corrosion is a process of oxidation, and there is nothing left to oxidise. Ferrite does not rust, does not need plating, does not need masking, and does not carry a coating temperature ceiling — and none of the coating design work described in magnet coatings compared applies to it at all.
| Grade | BHmax (MGOe) | Br (kG) | Hcb (Oe) | Hcj (Oe) | Typical use |
|---|---|---|---|---|---|
| Y25 | 1.6–2.0 | 3.7–4.1 | 2380–2780 | 2700–3100 | General purpose, holding, craft |
| Y30 | 2.6–3.0 | 3.9–4.1 | 2700–3100 | 3100–3600 | The commercial standard |
| Y30BH | 2.7–3.1 | 3.8–4.0 | 3000–3300 | 3400–3900 | Higher coercivity variant |
| Y33 | 3.0–3.3 | 4.1–4.3 | 2700–3200 | 3200–3800 | Motors, separation |
| Y35 | 3.3–3.8 | 4.3–4.6 | 2700–3300 | 3200–4000 | Loudspeakers, DC motors |
| Y40 | 3.8–4.2 | 4.4–4.8 | 2800–3400 | 3500–4500 | Premium; highest ferrite output |
The whole family spans roughly 1.6 to 4.2 MGOe. An ordinary N42 neodymium magnet sits at 42. Ferrite is not competing on energy density and never has been — a ferrite magnet doing an NdFeB magnet's job is typically eight to fifteen times the volume.
Ferrite is often quoted at 250–300 °C maximum operating temperature, with a Curie point around 450 °C. Both are true and neither is the constraint that matters in practice. The design-limiting behaviour is at the cold end, not the hot end — see below.
This is the single most important thing to know about ferrite, and it runs opposite to the intuition every engineer builds working with neodymium.
In NdFeB, coercivity falls as temperature rises, so hot is the dangerous condition and cold is safe. In ferrite, intrinsic coercivity falls as temperature falls. Hcj has a positive temperature coefficient of roughly +0.2 to +0.4 %/°C, meaning a ferrite magnet at −40 °C has substantially less resistance to demagnetisation than the same magnet at room temperature.
A ferrite circuit that is stable on the bench at 20 °C can irreversibly demagnetise in a cold chamber, in winter shipping, or in an outdoor or automotive under-hood cold soak. The loss is permanent and does not come back when the part warms up. Any ferrite design that will see sub-zero temperatures must have its operating point checked at the minimum temperature, using the demagnetisation curve at that temperature — not at 20 °C and not at the maximum.
The exposure is worst where the load line is already low: thin magnets, large air gaps, or circuits with a strong opposing field such as a motor at stall or high current. Those are exactly the circumstances in which a designer would have chosen a thin ferrite magnet to save cost.
Br meanwhile has a negative coefficient of about −0.2 %/°C, so ferrite actually gets slightly stronger as it cools even as it becomes easier to demagnetise. The two effects pull in opposite directions and that is precisely why the behaviour catches people out. The general method for working operating points at temperature is in magnets and temperature.
Ferrite is not a downgrade. It is the correct engineering choice whenever the constraint is cost, volume, corrosion or supply rather than size.
Dropping a neodymium magnet into a socket designed for ferrite — a popular upgrade — produces a field five to ten times stronger than the circuit was designed for. Hall sensors saturate, reed switches stop releasing, latch forces exceed the mechanism, and holding magnets become impossible to separate by hand. If you are substituting up, the magnet must be resized down to match the original field specification, not matched on physical dimensions.
Ferrite's commercial profile is the opposite of SmCo's: cheap, widely available, and forgiving on lead time. The specification issues are mechanical and dimensional rather than magnetic.
The only honest ferrite-versus-neodymium comparison sizes both materials to deliver the same field at the same working point, then compares delivered cost of the finished assembly including housing, mass and freight. Comparing them at the same physical size makes ferrite look useless; comparing them per kilogram makes it look free. Neither is the decision. See cost reduction and value engineering.
We stock ceramic ferrite in discs, rings, blocks and arcs, and source custom shapes including injection-moulded bonded ferrite. If you are weighing ferrite against neodymium on cost, we can size both to the same field requirement so the comparison is real.