Domain wall (magnetism)#Bloch wall

As Bloch- wall or Bloch wall is the term for magnetism the border between the white districts in ferromagnetic materials below the Curie temperature. It was named after the Swiss-American physicist Felix Bloch.

Description

Put two white districts with different - usually the opposite - direction of magnetization to each other, then the direction of magnetization changes fluent in the Bloch walls. The magnetization is always parallel to the wall plane, i.e., the magnetization rotates helical. By this rotation, the helical magnetization of the material surface from the plane is out and creates a stray magnetic field which is detected, for example, of the bitter technology. The size of the white areas (domains) is usually less than 100 microns and the thickness of the Bloch walls usually amounts to a few hundred atomic distances. The reason for the gradual transition lies in the energetic balance between the short-range exchange energy, which aligns the spins parallel within a white district, and the long-range dipole -dipole interaction, which tries to align the spins antiparallel. The Bloch- walls would be infinitely thick, would not the anisotropy. It helps because the spins point in the Bloch wall for the most part in so-called serious magnetization directions. The anisotropy energy is proportional to the domain wall thickness.

Bloch walls are held by lattice defects, grain boundaries, inclusions or internal stresses at the location. A hard magnetic material has many lattice defects and thus hinders the movement of domain walls strong. By applying an external magnetic field, the position of the Bloch walls changes by leaps and bounds - this is called Barkhausen jumps.