Heat's Effect on Magnets

Heating a magnet to the Curie temperature will deteriorate its magnetic properties.

A magnet is any device that is able to produce a magnetic field by arranging, in orderly lines, unpaired electrons. Magnets can occur in nature or be synthesized by man, and they are most often recognized for their ability to attract certain metals to themselves, such as iron. A material's magnetic properties are, however, subject to the ambient temperature of their environment. When exposed to high temperatures, their magnetic properties begin to fail.

Ferromagnetism

Ferromagnetic substances have naturally occurring parallel arrangements of unpaired electrons that create magnetic domains. These domains are the ultimate reason for a ferromagnet's magnetic properties. Any type of permanent magnet is a ferromagnet because it does not rely on the presence of an external magnetic field to cause its magnetism. The most famous ferromagnetic substance is iron.

Disrupting a Magnetic Field with Heat

Heat is a form of energy. When placed next to the magnetic substance, energy is given to the atoms, causing them to become more physically active in their movements. The presence of heat near a ferromagnet causes the parallel arrangements of unpaired electrons to move out of their previously stationary position. In doing so, the magnetic domains are broken, and the magnetic properties of the substance start to weaken. At higher temperatures, more energy is given to the atoms, and the magnetic properties lessen even further.

Curie Temperature

Named after the French scientist, Pierre Curie, the Curie temperature is the exact temperature to which a material must be heated whereupon it completely loses all of its magnetic properties. At the Curie temperature, which is represented in scientific equations as Tc, the unpaired electrons have no order anymore. They are moving around too quickly within the substance to be in any arrangement that could produce a magnetic domain. The Curie temperature for each magnetic substance on Earth will differ.

Paramagnetism

When a ferromagnetic material reaches the Curie temperature, it loses its classification as a naturally occurring ferromagnet and instead becomes a paramagnetic material. Paramagnetic materials can only maintain a magnetic field, and thus magnetic properties, when in the presence of an external magnetic field. The external magnetic field is able to temporarily realign the unpaired electrons, but they resume their random order when the field is removed. An example of an external magnetic field may be another magnet or source of electricity.

References

• NASA: Magnets and Heat
• PhysLink: Do Magnets Ever Lose Their Magnetism?
• Brigham Young University: Ferromagnetism
• NDT Resource Center: Diamagnetic, Paramagnetic and Ferromagnetic Materials
• Princeton University: Curie Temperature