Magnet FAQs

There are three types of magnets: permanent magnets, temporary magnets, and electromagnets

• Permanent magnets emit a magnetic field without the need for any external source of magnetism or electrical power.
• Temporary magnets behave as magnets while attached to or close to something that emits a magnetic field, but lose this characteristic when the source of the magnetic field is removed.
• Electro-magnets require electricity in order to behave as a magnet. 

There are many different types of permanent magnet materials, each with their own unique characteristics. Each material has a family of grades that have properties slightly different from each other, though based on the same composition

Modern permanent magnets are made of special alloys that have been found through research to create increasingly better magnets. The most common families of permanent magnet materials today are made out of aluminum-nickel-cobalt (alnicos), strontium-iron (ferrites, also known as ceramics), neodymium-iron-boron (a.k.a. neodymium magnets, or "super magnets"), and samarium-cobalt-magnet-material. (The samarium-cobalt and neodymium-iron-boron families are collectively known as the rare-earths). 

Rare Earth magnets are magnets that are made out of the rare-earth group of elements. The most common rare-earth magnets are the neodymium-iron-boron (neo magnets) and samarium cobalt (SmCo magnets). 

Soft iron and certain iron alloys, such as permalloy (a mixture of iron and nickel) can be very easily magnetized, even in a weak field. As soon as the field is removed, however, the magnetism is lost. These materials make excellent temporary magnets, like those used in telephones and electric motors

Electromagnets are used when very strong magnets are required. Electromagnets are produced by placing a metal core (usually an iron alloy) inside a coil of wire that carries an electric current. The electricity in the coil produces a magnetic field. The strength of the electromagnet depends on the strength of the electric current and the number of coils of wire. Its polarity depends on the direction of the current flow. While the current flows, the core behaves like a magnet, but as soon as the current stops, the magnetic properties are lost. Electric motors, televisions, maglev trains, telephones, computers, and many other modern devices use electromagnets. 

These are electrical currents that are induced when a magnetic field moves in relation to an electrical conductor that has been placed within reach of the magnetic field. In turn, these eddy currents create a magnetic field that acts to stop the relative motion of the original magnetic field and electrical conductor

If stored away from factors that adversely affect the magnet such as power lines, other magnets, high temperatures etc., a magnet will retain its magnetism essentially forever. 

Factors that can affect a magnet's strength include:

• Heat
• Radiation
• Strong electrical currents in close proximity to the magnet
• Other magnets in close proximity to the magnet
• Neo magnets will corrode in high humidity environments unless they have a protective coating.

Shock and vibration do not affect modern magnet materials, unless sufficient to physically damage the material. 

Modern magnet materials do lose a very small fraction of their magnetism over time. With samarium cobalt magnets, for example, this has been shown to be less than 1% over a period of ten years. 

The most powerful magnets available today are the rare- earth types. Of the rare-earths, neodymium magnets are the strongest. However, at elevated temperatures (of approximately 150°C and above), samarium cobalt magnets can be stronger than neo magnets, depending on the magnetic circuit

Once a magnet is fully magnetized, it's "saturated" and cannot be made any stronger. In that sense, magnets are like buckets of water: once they are full, they can't get any "fuller". 

Provided that the material has not been damaged by extreme heat, most magnets can be re-magnetized back to their original strength. 

Most commonly, Gaussmeters, magnetometers, or pull-testers are used to measure the strength of a magnet. Gaussmeters measure the strength in Gauss; Magnetometers measure in Gauss or arbitrary units (making it easy to compare one magnet to another); pull-testers measure pull in pounds, kilograms, or other force units. Helmholtz Coils, search coils and permeameters are also used to make sophisticated measurements of magnets.

No. The B_r value is measured under closed-circuit conditions. A closed-circuit magnet is not of much use. In practice, you will measure a field that is less than 12,300 Gauss close to the surface of the magnet. The actual measurement will depend on whether the magnet has any steel attached to it, how far away from the surface you make the measurement, and the size of the magnet (assuming that the measurement is being made at room temperature).

For example, a 1" diameter Grade 35 neodymium magnet that is ¼" long will measure approximately 2,500 Gauss when 1/16" away from the surface, and 2,200 Gauss when 1/8" away from the surface. 

The strength of a magnetic field drops off more or less exponentially over distance.

Here is an example of how the field (measured in Gauss) drops off with distance for a samarium cobalt Grade 18-disc magnet which is 1" in diameter and 1/2" long:

For a circular magnet with a radius of R and length L, the field B_x at the centerline of the magnet at distance X from the surface can be calculated by the following formula, where B_r is the residual induction of the material):

There are additional formulae that can be used to calculate the field from a rectangular magnet and magnets in other configurations.

Only materials that are attracted to a magnet can "block" a magnetic field. Depending on how thick the blocking piece is, it will partially or completely block the magnetic field. 

Magnetic poles are the surfaces from which the invisible lines of magnetic flux emanate and connect on return to the magnet. 

The north pole is defined as the pole of a magnet that, when free to rotate, seeks the north pole of the earth. In other words, a magnet's north pole will seek the earth's north pole. Similarly, the south pole of a magnet seeks the south pole of the earth. 

Lines of force are three-dimensional, surrounding a bar magnet on all sides.

Like poles repel and unlike poles attract. When opposite poles of a magnet are brought together, the lines of force join up and the magnets pull together.

When like poles of a magnet are brought together, the lines of force push away from each other and the magnets repel each other.

Most modern magnet materials have a "grain" in that they can be magnetized for maximum effect only through one direction. This is the "orientation direction", also known as the "easy axis", or "axis".

Un-oriented magnets (also known as "Isotropic magnets") are much weaker than oriented magnets, and can be magnetized in any direction. Oriented magnets (also known as "Anisotropic magnets") are not the same in every direction - they have a preferred direction in which they should be magnetized. 

Yes, magnets can be machined. However, hard magnet materials are extremely difficult to machine, unlike flexible or rubber-type magnet materials. Magnets should be machined in the unmagnetized state as much as possible, using diamond tools and/or soft grinding wheels. In general, it is best not to try to machine hard magnet materials unless you are familiar with these specialized machining techniques. 

Magnetic Assemblies consists of one of more magnets, along with other components, such as steel, that generally affect the functionality of the magnet.

If a magnet must be fastened to a device, you can use either mechanical means or adhesives to secure the magnet in place.

Adhesives are often used to secure magnets in place. If magnets are being adhered to uneven surfaces, an adhesive with plenty of "body" is required so that it will conform to the uneven surface. Hot glues have been found to work well for adhering magnets to ceramics, wood, cloth, and other materials. For magnets being adhered to metal, "super glues" can be used very effectively.

Most stainless steel types are not magnetic, which means they cannot be attracted to a magnet. These are known as austenitic stainless steels, such as the popular grades 304 and 316. However, some types of stainless steel are magnetic, such as ferritic and martensitic stainless steels.

So, if the stainless steel is made of a magnetic grade, then magnets will stick to it. If it's not magnetic, then the magnets will not stick to it. It's important to note that the strength of the magnetic attraction may vary depending on the grade of stainless steel and the strength of the magnet.

Magnetism is a property exhibited by certain materials that enables them to attract or repel other materials. When we talk about metals, their magnetic properties can vary widely depending on the specific metal and its atomic structure. Here's a general overview of the magnetic behavior of metals:

1. Ferromagnetic Metals: These are metals that are strongly magnetic. They can be magnetized and retain their magnetism even after the external magnetic field is removed. Common examples of ferromagnetic metals include iron, nickel, and cobalt. These metals have unpaired electrons in their atomic structure, which align themselves in a way that creates a strong magnetic field.
2. Paramagnetic Metals: Paramagnetic metals are weakly magnetic, meaning they are attracted to an external magnetic field but do not retain their magnetism once the field is removed. These metals have some unpaired electrons, but their atomic structure does not allow for strong magnetic alignment. Some examples of paramagnetic metals are aluminum, titanium, and platinum.
3. Diamagnetic Metals: Diamagnetic metals are non-magnetic and are repelled by magnetic fields. Their atomic structure does not contain unpaired electrons that can create a magnetic field. Most metals, such as copper, silver, and gold, fall into this category. However, it's important to note that the diamagnetic effect in these metals is generally very weak and often overshadowed by other factors.

It's worth mentioning that the magnetic properties of metals can also be influenced by factors like temperature. For example, some metals that are non-magnetic at room temperature may become weakly magnetic at low temperatures, exhibiting a phenomenon known as "ferromagnetic transition."

In addition to metals, there are also magnetic alloys, which are mixtures of different metals or metals with non-magnetic elements. Alloys like steel, which is a combination of iron and carbon, can exhibit magnetic properties depending on the specific composition and processing techniques used.

Overall, while there are metals that are magnetic (ferromagnetic and paramagnetic), many common metals are non-magnetic (diamagnetic). The magnetic behavior of a specific metal depends on its atomic structure and the presence or absence of unpaired electrons.