You are currently viewing <strong>Loss of Magnetization and Demagnetization of Permanent Magnets</strong>
magnets loss of magnetization demagnetization

Loss of Magnetization and Demagnetization of Permanent Magnets

When purchasing magnets you want them to maintain their full performance as long as possible. What are the best practices to use and store them properly? Is a magnet going to lose its magnetization over time? What circumstances can compromise a magnet temporarily or permanently? In this article you will find all the answers.

Do magnets lose their strength and magnetization over time?

Yes, magnets do lose some performance over time. This process is natural and very slow, though. A standard permanent neodymium magnet, kept in proper storage conditions and not subjected to other external factors, will lose on average less than 5% of its magnetization in a span of an entire century!

The stronger the magnet, the longer the conservation of its magnetization against time and external factors. This resistance to changes to the magnetic field is called coercivity. Neodymium magnets have more coercivity than ferrite ones.

Even a ferrite permanent magnet will not lose much of its magnetization over time. Depending on storage conditions and usage, the loss amounts to less than 2% a year on average, although some other sources estimate an approximate 10% strength loss in 100 years.

What can cause magnets to demagnetize?

The main reasons are exposure to: heat or cold temperatures, strong magnetic fields, AC electric currents, strong vibrations, strong impacts, structural damage, oxidation, corrosion and radiation.

Here the list of all causes of demagnetization explained in detail:

See also:

Loss of Magnetization caused by heat exposure

Heating magnets beyond working temperature can cause a loss of magnetization
Heating magnets beyond working temperature can cause a loss of magnetization

Exposing a magnet to high temperatures can decrease its strength or permanently damage its structure. Usually this happens at very high temperatures, but for certain neodymium magnets this can happen as low as 60°C.

Magnets are characterized by two temperature thresholds: the working temperature and the Curie temperature. These are important parameters to evaluate magnets performance and resistance when exposed to heat.

What is the working temperature of a magnet?

The working temperature is the maximum temperature a magnet can withstand for prolonged periods of time without incurring in a loss of performance, either temporary or permanent.

What is the maximum working temperature for a neodymium magnet?

The working temperature of standard Neodymium magnets is 80°C. Special neodymium magnets can be manufactured to have a higher temperature tolerance. This is indicated by a letter written after the grade of magnetization. A neodymium magnet with an “M” (like N35 M) can be heated up to 100°C. An “H” magnet up to 120°C, “SH” up to 150°C, “UH” up to 180°C, “EH” up to 200°C, and a “TH” up to 220°C. Our standard neodymium magnets (no letter shown) have a working temperature of up to 80°C; ask our team if you need neodymium magnets with higher heat tolerance.

What is the maximum working temperature for ferrite and Alnico magnets?

Ferrite and especially Alnico magnets have a very high maximum working temperature. Ferrite magnets can operate at a temperature of up to 250°C, while Alnico magnets up to 650°C.

What is the Curie temperature of a magnet?

The Curie temperature is the temperature above which a magnet loses all of its magnetization permanently. In this case, the structure is compromised beyond repair and remagnetization is no longer possible.

Which is the Curie temperature for a neodymium magnet?

Standard neodymium magnets have a Curie temperature of 310 °C (340-350°C for special M, H, SH, UH, EH, TH magnets).

Which is the Curie temperature of ferrite and alnico magnets?

The Curie temperature of Ferrite magnets is 450°C, while for Alnico Magnets is 700–850°C.

What happens if you heat a magnet above its maximum working temperature?

Heating a magnet above its maximum working temperature will cause a temporary or permanent loss of magnetization (adhesive force). The end result will change based on how much the heat exceeds the working or (eventually) the Curie temperature of the magnet.

Here are three different scenarios:

Temporary loss of performance

If the heat reaches values just above the maximum working temperature, the magnet will lose some magnetic strength while it remains hot.

Neodymium magnets lose about 0.11% of their strength for each 1°C in excess above the working threshold. This loss can be recovered by cooling the magnet.

The end result is not affected by either duration of the exposure nor the amount of times a magnet is heated and cooled. Be careful nevertheless, because repeated and rapid heating and cooling cycles can cause the magnet to break or crack. Magnets that have to be used in critical environments should be designed accordingly (shape, size and choice of materials). Ask our technical team for assistance.

Permanent loss of performance

If the heat reaches values significantly higher than the maximum working temperature, the magnet is weakened permanently. Cooling it down may recover some magnetization, but some of the loss will be permanent.

However, provided that the Curie temperature was not reached, this loss is recoverable by exposing the magnet to a sufficiently strong external magnetic field. This process of remagnetization (similar to what happens during manufacturing) can remagnetize a weakened magnet and restore its original strength.

Irreversible loss of magnetization

If the heat surpasses the Curie temperature, the structure of the magnet is altered permanently and the loss of magnetization cannot be recovered. Remagnetization is no longer possible.

Important Notes

The shape and size of a magnet, together with the direction of magnetization (axial or diametrical, for example) can substantially change its heat tolerance.

Moreover, the time of exposure can make a difference for larger magnets. The outer part can reach critical temperatures while the core can be less impacted, resulting in an irregular magnetization. Anyway, even if just a portion of the magnet exceeds the working temperature or Curie temperature thresholds, the damage happens regardless, and prolonged exposure does not make much of a difference.

Contact our technical team for further specifications about our magnets and an evaluation of your use case.

Loss of magnetization due to very cold temperatures exposure

Exposure to very cold temperatures can be detrimental for ferrite magnets
Exposure to very cold temperatures can be detrimental for ferrite magnets

Can a magnet be damaged by cold temperatures?

A magnet exposed to very cold temperatures can experience a loss of performance, but this happens very differently depending on the magnetic material. Ferrite magnets are easily damaged while neodymium ones have a totally different behavior.

Is it ok to expose neodymium magnets to very cold temperatures?

Actually, Neodymium magnets become slightly stronger up to -125°C. Beyond this threshold the magnetic force will steadily decrease. At -196 °C (as when immersed in liquid nitrogen), only about 85-90% of the magnetization is retained. When brought back above 125°C the adhesive force will be fully restored to original values.

Can ferrite magnets be damaged by cold temperatures?

Yes, ferrite magnets can incur a permanent loss of magnetization when exposed to temperatures below -40°C.

Magnetic products different from standard magnets are even more susceptible to low temperatures. For example, magnetic tapes and sheets can already be damaged at temperatures of -20°C.

Shocks, Falls and Impacts affectting permanet magnets

Can a Magnet be damaged or lose magnetization due to shocks, falls or strong impacts?

Modern permanent magnets should not be affected. Provided that the magnet doesn’t break or crack, dropping or hitting it should not weaken its magnetization. The stronger the magnet, the higher its coercivity will be (resistance to a loss of magnetization). Weaker permanent magnets or non-permanent ones can be affected.

Permanent magnets are usually quite brittle and, if part of the magnet is chipped away, this will inevitably result in a loss of magnetic strength.

Vibrations affectting permanet magnets

Can vibrations damage a magnet?

Modern permanent magnets are not very affected by vibrations. The stronger the magnet, the higher its coercivity will be (resistance to a loss of magnetization). Weaker permanent magnets or non-permanent ones can lose some strength after being exposed to strong vibrations.

Welding effects on permanet magnets

Welding a magnet or close by can cause a loss of magnetization
Welding a magnet or close by can cause a loss of magnetization

Can welding a magnet or close to it cause a loss of magnetization?

Welding on or in close proximity to a magnet can lead to a loss of magnetization. This may be caused by the heat or by the electric current generated from the welding process.

Radiation exposure on permanent magnets

Does radiation damage a magnet?

Radiation, especially at high levels and for prolonged periods of time, can result in flux changes of the magnet. Magnets employed in high radiation environments require specific evaluations during the design stage.

Rust and Oxidation affecting permanent magnets

Corrosion and oxidation is detrimental to magnets performace
Corrosion and oxidation is detrimental to magnets performace

Can a Magnet be damaged by water and oxidation?

Yes, most magnets incorporate a high dose of iron (more than 60% in neodymium magnets) and are prone to rust and oxidation when exposed to humid environments and water. Since all these factors alter the chemical structure of the magnetic material, it leads to a loss of strength. Neodymium magnets can be protected by anti-corrosion coatings like rubber (ask our team about this and other options to protect your magnets). Ferrite magnets are made from iron-oxide instead (about 90%) and, as a result, they do not corrode even when submerged in water.

Effects of External magnetic fields on permanent magnets

At the time of manufacturing, magnets are magnetized by a very strong magnetic field. This process alters the chemical composition of the material and also its crystalline microstructure, giving the permanent magnet its magnetic properties (like the attraction to other ferromagnetic materials such as steel, iron, nickel, cobalt or the attraction/repulsion to other magnets).

Can a magnet be damaged if exposed to other magnetic fields?

Yes, leaving a permanent magnet close to other strong magnets or electromagnets can lead to a loss of magnetization over time. The magnetic field generated by stronger magnets inevitably weakens that of weaker magnets, if kept in contact or in close proximity for prolonged time.

A magnet’s coercivity defines its strength and capacity of maintaining its magnetic structure and orientation. Strong neodymium magnets have a higher coercivity compared to ferrite and alnico magnets, so you should be more careful. You should avoid keeping strong magnets with different orientations close together. Stacking them in piles (with the same orientation) is the correct way of storing them.

Magnets exposed to electric AC current

What happens to permanet magnets if exposed to AC electric current?

Subjecting the magnet to an AC current with sufficient intensity to overcome its coercivity can slowly weaken the magnet, eventually decreasing its magnetic field to zero. This is the way commercial demagnetizers work, which are commonly used to demagnetize tools, erase credit cards and hard disks.

Be aware that different magnets can have different conductivity, and the resistance to an electric current passing through can generate a lot of heat. This can be dangerous as well as damaging to the magnet.

DC current can actually be used to magnetize a ferromagnetic material, but if you subject the same magnet to AC, the previously obtained alignment of its structure will be disrupted by the changes in frequency.

Magnetism and conduction are two distinct properties of a material. This means that there are magnets like neodymium ones (60% + iron content) with a good electrical conductivity, while ferrite magnets are very poor conductors (iron oxide).

Magnetization process for a ferromagnetic material

How to demagnetize a magnet

How can you demagnetize a magnet?

The most reliable way to demagnetize a magnet is with an electrical demagnetizer tool. It uses AC current to generate an irregular magnetic field, able to affect permanent magnets. There are simpler tools that do not rely on electricity, but are mainly used to temporarily magnetize and demagnetize ferromagnetic materials like the tip of a screwdriver (but not effective against strong permanent magnets).

There are several other ways a magnet can lose its magnetization, but these strongly depend on the properties of the material (ferrite, neodymium, alnico) and the strength (coercivity) of the magnet. These are exposure to: heat, cold temperatures, strong magnetic fields, strong impacts, strong vibrations, mechanical damage or chemical damage (oxidation and corrosion).

How to properly store a magnet

how to store your magnets storage to avoid demagnetise
Example of a correct storage method for magnets

How should you store your magnets properly in order to prevent demagnetization?

To prevent any loss of magnetic strength and performance, keep your magnets in a dry and protected place. Avoid temperatures below -40°C for Ferrite Magnets and above 80°C for standard Neodymium Magnets. Do not expose them to strong electric current or magnetic fields or strong vibrations. If you store multiple magnets together, stack them together in piles. Avoid keeping strong magnets in close vicinity to one another. Permanent magnets are quite brittle, so strong impacts can chip or crack its structure, resulting in a loss of performance. Neodymium magnets are vulnerable to oxidation and corrosion, so exposure to water and humid environments should be avoided.

For further assistance about our products, technical support, products documentation and custom designed products, do not esitate to contact our team! We offer multilingual support by mail or phone.