THE CENTERS OF DOMAIN NUCLEATION IN HARD MAGNETIC TBFECO-FILMS WITH INPLANE UNIAXIAL ANISOTROPY

The domain development during the magnetization reversal is studied in TbFeCo films with field-induced in-plane anisotropy (Kin ≈ 105 Jm-3) by means of a Kerr-microscope which is equipped with an electronic image processing system. The nucleation of the domains does not take place at the film edge, but rather at defects which have a strongly deviating polar component of their easy axis. The coercivity of the films is determined by wall friction. The threshold against the nucleation of reversed domains is taken at a lower external field. Nevertheless, the hysteresis curves in the easy direction are very steep due to the viscous continuous motion of the walls after domain nucleation. The reversal preferably starts at line defects that are perpendicular to the easy axis because of the demagnetizing fields that support the reversal. A unique relationship between the polar M-components in defects and the in-plane M in the adjacent regions is caused by a tilt in the local easy anisotropy axis within the defect. The nucleation starts in the polar region with the tilted anisotropy where the external field forces the in-plane M-component and along with it the polar component to reverse. Point defects (pinholes) carry a ring with tilted polar easy axis at their edges. The tilt in this axis has cylindrical symmetry. © 1990 IEEE