Demagnetization

 

The Demagnetization (literally „Entgaußung”) is a process by which a permanent magnet or a long-term-magnetically become ferromagnetic material loses his magnetic polarization all or part.

 

Procedure

Materials mostly are demagnetized by an only strong change magnetic field which fades away then bit by bit. This magnetic field must be so strong that the "Koerzitiv"fieldstrength of the magnetized material is reached. A change of the magnetization of the long-term-magnetic materials with decreasing amplitude occurs through the change field. With it the Hysteresekurve with decreasing amplitude of the magnetic field strength and the magnet flux density will run through, until the permanent magnet field Zero is.

 

In the accompanying picture one begins, for instance, on the top right, then it goes always oppositely for the clockwise to the left below, then again to the right on top, but no more so far, etc. If after many circulations the smallest loop in the intersection of both axes is reached, one can switch off the external magnetic field, the iron is demagnetized to a great extent.

 

For the assuagement of the change field there are two methods: Either one slowly removes a portable electromagnet which is pursued with 50 Hz, or one lays in row to the coil a cold leader who allows to become lower the stream. 5 to 10 Ummagnetisierungen are most enough.

An demagnatization can also be caused by mechanical vibrations or heating up ferromagnetischer materials after the curie temperature.