DOMAIN-WALL PINNING IN AMORPHOUS COZRNB FILMS

A series of CoZrNb amorphous films, with thickness t ranging from 200 to 630 nm, has been studied by using several techniques: Kerr imaging, dc and audio frequency hysteresis loops, field dependence of the perm eability, torque balance, broadband frequency susceptometer (1 kHz < f < 500 MHz). Only samples with t < 500 nm have simple domain structure s typical of an in-plane anisotropy (with a small dispersion of the ea sy axis). Although domain walls (DW) are visible, they do not contribu te to the initial permeability in the observed frequency range (even i n the favorable case where the magnetic field is parallel to the easy axis), but they do play a role on the irreversible magnetization proce sses as shown by the existence of a critical field H(cr), typical of t he onset of irreversible DW motion. These observations are consistant with a model which assumes that the DW are pinned at the film surfaces : the calculations give a negligible DW bulging contribution to the in itial permeability, and predict the occurence of a DW unpinning field, thickness dependent as observed.