How Does a Magnet Lose Its Magnetism?

By Michael Keenan; Updated April 24, 2017
Magnets and iron shavings.

What Makes a Magnet Magnetic?

molecules are aligned through polarization.

Most magnets today are made from alloys. Some of the most common alloys are aluminum-nickel-cobalt, neodymium-iron-boron, samarium-cobalt and strontium-iron. In order to magnetize the alloy, the alloy is exposed to a magnetic field, which actually alters structure by realigning the the molecules into lines through a process known as polarization.

Heat

Heat destroys polarization.

For each material of magnet, there is a Curie temperature, or temperature at which the heat will destroy the polarization of the material, causing it to loses its magnetic properties. These former magnets can be re-magnetized in the same way the alloys are magnetized for the first time. Temperatures lower than the Curie temperature can weaken a magnet, but the magnetism will usually return to full strength when it is returned to normal temperatures.

Stronger Magnetic Fields

Magnet

The higher a magnet's coercivity, the more likely it will retain its magnetic characteristic even when stuck in a magnetic field of opposite polarity. Some magnetic materials, such as ceramic, have low coercivities, so they can have their magnetic qualities removed more easily. With stronger magnets, opposite magnets are sometimes applied to decrease their magnetic power so they're not too strong to be used.

Time

Time demagnetizes magnetic objects.

Time is a very ineffective means of demagnetizing a magnetic object. Magnets only lose their magnetic powers very slowly. For example, samarium cobalt magnets might decrease their magnetic strength about 1 percent over a decade.

Electromagnets

Copper coils.

Another type of magnet is an electromagnet. The material becomes magnetic when a electrical current is passed through it. However, the material will no longer be magnetic when the electricity stops.

About the Author

Mark Kennan is a writer based in the Kansas City area, specializing in personal finance and business topics. He has been writing since 2009 and has been published by "Quicken," "TurboTax," and "The Motley Fool."