Coercivity

As the magnetic coercivity ( volume Hc, H for the magnetic field strength and c is coercivity of Latin coercere = hold together ) is defined as the magnetic field strength, which is necessary to completely demagnetize a ferromagnetic substance, so that the resulting total flow or the local flux density is zero. The higher the coercive force, the better retains a magnetic its magnetization when exposed to a counter-field. The SI unit is, as in all magnetic field strengths. Occasionally, the traditional unit is still Oe ( Oersted ) used.

Become a ferromagnetic or ferrimagnetic materials exposed to a magnetic field, there remains even after removal of the field, residual magnetism, the remanence. This also applies to spin glasses, albeit in a weakened form.

Similarly, it is called the electric field strength that is needed to remove the residual dielectric displacement ( polarization) of a ferroelectric, coercive electric field. The higher it is, the better the ferroelectric retains its polarization, in particular the substance associated with the piezoelectric properties ( piezoelectricity ).

Application

A distinction between the coercive force (HCB ), the magnetic flux density and the coercive force (HcJ ) of the magnetic polarization. A permanent magnet field strength HcB exposed to magnetic flux density in the magnet disappears. However, it is still magnetically after removal from the field. Only at a demagnetizing field strength HcJ of the permanent magnet loses its magnetic polarization, and thus its magnetization completely, that is the applied field strength causes magnetic flux density of the size μ0 · H, so that or, in this point of the material with respect to its magnetic properties, such as vacuum about how air behaves.

In the same way, one can also define the coercive electric field.

Note the strong temperature dependence of the field strength, which is not least to look in the temperature dependence of ferromagnetism or ferroelectricity.

Measurement

The rate of the magnetic coercivity with a so-called coercimeter which measures the polarization over induction in a moving coil in response to an applied external magnetic field strength. Since the magnetization and thus the remanence and the coercive field on the microstructure of the material depends, can be derived from the magnetic properties of knowledge about the structure of the material (eg, degree of deformation ).

To measure the coercive electric field, fixed electrodes are vapor-deposited or applied to the liquid to be tested substance. The arrangement corresponds to that of a parallel plate capacitor. From the applied voltage and the measured drive loads can be determined, together with the dimensions of the electric field strength and the dielectric displacement. From the graphical representation of the hysteresis curve, can be as shown in the picture, read the coercive electric field.

Values

Literature

  • Horst Kuchling: Paperback physics. 4th edition, published by Harry German, Frankfurt am Main, 1982
  • Günter Springer: electrical engineering expertise. 18.Auflage, publishing - Europe - teaching aids, Wuppertal, 1989, ISBN 3-8085-3018-9
  • Hans Fischer: Materials in electrical engineering. 2nd edition, Carl Hanser Verlag, Munich, Vienna, 1982 ISBN 3-446-13553-7
  • Horst Stöcker: Paperback physics. 4th edition, published by Harry German, Frankfurt am Main, 2000, ISBN 3-8171-1628-4
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