Domain wall pinning in sputtered soft amorphous magnetic thin films

Abstract

Domain wall pinning in sputtered soft amorphous thin films has been observed similar to that seen in rapidly quenched amorphous ribbon. The pinning is induced by annealing samples in their nonsaturated state. The easy-axis hysteresis loop of such a sample shows a characteristic stop in the change of magnetization at a nonsaturated magnetization value for both an increase and decrease of applied field, corresponding to the field value when the domain walls are pinned. An abrupt increase of magnetization is observed when the pinning is overcome by a large enough applied field, called wall pinning force (Hp). Sputtered amorphous Fe5.85Co72.15Mo2B15Si5 thin films with coercivity of about 0.06 Oe and thickness of about 6500 Å gave a wall pinning force as high as 0.6 Oe. The general mechanism of the wall pinning was confirmed by domain viewing. For different annealing temperatures, the wall pinning force increases as the annealing duration increases and approaches a maximum value. A linear relation between the maximum value of wall pinning force and the field-induced magnetic anisotropy field was obtained.