What is a Bloch wall in magnetism



As Bloch wall or Bloch's wall In magnetism, one denotes the boundary between the Weiss areas in ferromagnetic substances below the Curie temperature. It was named after the Swiss-American physicist Felix Bloch.

Bump two Weiss districts with different - mostly opposite - magnetization directions on one another, the direction of magnetization in the Bloch walls changes fluently. The magnetization is always parallel to the wall plane, i.e. i.e. the magnetization rotates helically. This helical rotation shows the magnetization on the material surface out of the plane and a magnetic stray field is created, which z. B. is detected by the bitter technology. The distances between the Bloch walls are around 100 ┬Ám and their thickness around 30 nm. The reason for the gradual transition is the energetic compromise between the short-range exchange energy that occurs within a Weiss district aligns the spins in parallel, and the long-range dipole-dipole interaction that tries to align the spins antiparallel. The Bloch walls would be infinitely thick if it weren't for the anisotropy energy. It contributes because most of the spins within the Bloch wall point in so-called heavy magnetization directions. The anisotropy energy is proportional to the Bloch wall thickness.

Bloch walls are held in place by lattice defects, grain boundaries, inclusions or internal stresses. A hard magnetic material has a lot of lattice defects and thus greatly hinders the movement of the Bloch walls. When an external magnetic field is applied, the position of the Bloch walls changes abruptly - this is called Barkhausen jumps.

Categories: Magnetism | Solid state physics