Why Does Heat Demagnetize Magnets?

Magnets can be used in many different applications to accomplish many different tasks. However, there are some places magnets simply cannot go. If a magnet is exposed to extremely hot temperatures, it will become demagnetized—that is, it will go from a powerful tool to a useless lump. There are four main types of magnetic material—ceramic, alnico, samarium cobalt, and neodymium—and each of these different material types has a different optimal temperature range. For all but the most extreme applications (say, entering a volcano), there is a magnet material that will be able to fit your needs.

Heat Affects Magnets in 3 Ways: Reversible Loss, Irreversible Loss, and Permanent Loss.

Reversible loss refers to the gradual loss in magnetic performance a magnet experiences as it is exposed to temperatures approaching—but not exceeding—its maximum operating temperature. When a magnet is cooled again, it will be just as strong as it was before being exposed to high temperatures. A magnet’s maximum operating temperature is the temperature where a magnet will begin to experience irreversible losses in performance. If a magnet experiences irreversible losses, it means that even after a magnet is cooled again, its performance will remain weaker than it was prior to being heated. Theoretically, a magnet that has experienced irreversible losses can be remagnetized and return to its original strength, although this is not a cost-effective approach. Finally, if a magnet experiences permanent loss, it means it has been heated to its Curie temperature and the structure of its magnetic domains have been permanently changed. No amount of remagnetization can restore a magnet after reaching this point.

Avoid Irreversible Loss of Magnetic Strength

Because Curie temperature represents an extreme loss of magnetic properties, it is best to choose a magnet based on its maximum operating temperature in order to avoid irreversible loss of magnetic strength. Of the four main magnetic materials, alnico magnets have the highest maximum operating temperature. Alnico magnets will not suffer irreversible performance losses until reaching 535°C, or 1000°F. In second place, we find samarium cobalt magnets, with a maximum operating temperature of 300°C, or 572°F.  Ceramic magnets are in third place, with a maximum operating temperature of about 250°C, or 480°F. Finally, in last place, we see neodymium magnets, with a typical maximum operating temperature of 80°C. While standard neodymium magnets have a maximum operating temperature of 80°C, or 176°F, new high temperature neodymium magnets have been developed. These high temperature neodymium magnets can be safely used at temperatures of up to 150°C, or 302°F with some special grades capable of performing at temperatures of up to 200°C, or 392°F.

For assistance in selecting the best magnetic materials for your application, Contact BuyMagnets.com today.