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White districts

In magnetism, the term "delimited areas" with the same polarization is understood to mean those areas of Weiss (or even white districts). They occur as microscopically small, magnetized domains in the crystals of a ferromagnetic substance. The name comes from their discoverer Pierre-Ernest Weiss, a French physicist who spent his entire life extensively studying magnetic phenomena.

Explanation of the Weisser districts

Ferromagnetic materials such as iron consist of a number of small elementary magnets that have a uniform direction of magnetization within a domain (Weissscher district). Weiss had this knowledge in 1907 when he examined the magnetic moments of the atoms. The Weiss districts are separated by so-called Bloch walls (magnetization transitions between the Weiss districts). In non-magnetic materials, the Weiss districts are magnetically disordered and thus behave neutrally outwards.

The orientation of the Weiss domains (naturally magnetized to saturation) is based on the crystal lattice of the material. Bringing an increasing magnetic field close to the material, first the Bloch walls of those Weiss areas move, pointing already in the direction of the external magnetic field. If the outer field continues to be amplified, the other domains change their polarity and fuse together.

Is it possible to visualize white areas?

The Weiss domains could be visualized in physics by several methods:

  • With the help of a macroscopic model one can see the orientation of the Weissian districts. For this, a rotatable amount of compass needles is placed on a surface. If the needles come too close, they are influenced by the neighboring magnetic fields and align themselves in parallel. This effect can be accelerated by the influence of temperature or vibrations.
  • Of course, the Bloch walls only become visible at the microscopic level. It positions ferromagnetic particles such as iron dust on another ferromagnetic material. Thanks to its magnetic properties, the dust is directed towards certain areas, the Bloch walls of the Weiss districts.
  • The moment of the polarity reversal can also be audible. For this, the successive increase of the magnetic field with a coil must be inductively recorded and amplified. With every change in the external field, the hysteresis of the Weiss domains makes it possible to hear a noise that makes the properties of the ferromagnetic material describable.
The Weißschen districts play an important role in ferromagnetism. Even if the field strength disappears (for example, the coil is de-energized), it still has someremanence, making the material look like apermanent magnetacts. Thus, the Weiss districts find their application in storage methods, for example in magnetic tapes, magnetic disks or floppy disks.