Magnet - Demagnetizing Ferromagnets

Demagnetizing Ferromagnets

Magnetized ferromagnetic materials can be demagnetized (or degaussed) in the following ways:

• Heating a magnet past its Curie temperature; the molecular motion destroys the alignment of the magnetic domains. This always removes all magnetization.
• Placing the magnet in an alternating magnetic field with intensity above the material's coercivity and then either slowly drawing the magnet out or slowly decreasing the magnetic field to zero. This is the principle used in commercial demagnetizers to demagnetize tools and erase credit cards and hard disks and degaussing coils used to demagnetize CRTs.
• Some demagnetization or reverse magnetization will occur if any part of the magnet is subjected to a reverse field above the magnetic material's coercivity.
• Demagnetisation progressively occurs if the magnet is subjected to cyclic fields sufficient to move the magnet away from the linear part on the second quadrant of the B-H curve of the magnetic material (the demagnetisation curve).
• Hammering or jarring: the mechanical disturbance tends to randomize the magnetic domains. This will leave some residual magnetization.