Coercivity

What does magnetic coercivity mean?

Coercive field strength is the magnetic field strength that is necessary to completely demagnetize a ferromagnetic material so that the resulting total flux or local flux density is zero. It is given with the unit Hc - H for the magnetic field strength and c for coercivity of Latin coercere = tame, hold together. The higher the coercivity, the better a magnet retains its magnetization when exposed to an opposing field (see also Remanence).

What types of coercivities exist?

Basically, one differentiates between:

  • The coercive force bHc of the flux density
  • The coercive force jHc of the polarization

As soon as a magnet is subjected to the demagnetizing field strength bHc, the magnetic flux density disappears in its interior. Nevertheless, he remains magnetic. This is due to the fact that the flux density generated by it is exactly the same as that of the demagnetizing field. As a result, both cancel each other out. With a coercive force of jHc, however, he loses his magnetization completely. The reason for this is that it dissolves its polarization.

A unit of measure for the strength of the magnetic field is usually A / m (= ampere per meter). Often, however, one still encounters the old unit Oe (= Oersted).

How to measure the coercivity?

The magnetic coercivity can be measured with a so-called coercemeter. This measuring device indicates the polarization via induction in a moving coil - depending on an applied external magnetic field strength. The magnetizability and thus also the coercive field strength or the remanence (residual magnetism) depend on the microstructure of the respective material (eg ferrite, hard metal, etc.). Accordingly, knowledge about the material structure (e.g., degree of deformation) can also be derived from the magnetic properties. Graphically, the coercive field strength can be represented by a hysteresis curve.


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