Computer simulation of wall pinning effect and intrinsic coercivity of thin domain walls

Abstract

A computer simulation technique is used to study the intrinsic coercivity of a thin (∼ a few atomic layers) domain wall in perfect ferromagnetic crystals, and the domain wall pinning due to the existence of different kinds of defects. A one spin relaxation process is used to minimize the total energy of the system which includes anisotropy, exchange and Zeeman energies. When the applied field is less than the intrinsic coercivity, the equilibrium domain wall remains stationary. At higher fields the wall starts to move through the perfect parts of the crystal. When the domain wall approaches defect sites, it comes to a stop and is pinned by the defects. If the defect is a vacant line then the equilibrium domain wall bows out; the amount at bending of the wall increases with increasing field. The wall breaks free from the defects only when the applied field is increased up to a new critical value. The domain wall energy shows a periodic behavior during the wall motion in the perfect part of the crystal. But the wall energy decreases and forms a deep well around the imperfection. This energy trap results in an increase of coercivity. The increment of coercive force depends on the concentration and the kinds of defects.