Influence of surface roughness on magnetic properties of Fe-Si-B amorphous alloys

Influence of surface roughness on magnetic properties of Fe78Si9B13 and Fe78Si14B8 amorphous alloy ribbons was investigated. Magnetic induction in an external field of 800A/m, B8 of Fe78Si9B13 ribbon increased slightly with decreasing surface roughness, while iron loss W13/50, at 1.3T 50Hz excitation, remained almost at the same level. In Fe78Si14B8 amorphous alloy, however, quite different behaviors were observed. Both B8 and W13/50 were improved remarkably with decreasing surface roughness of the ribbon. Fe78Si14B8 amorphous ribbon showed as good a magnetic performance as Fe78Si9B13 only if it had smooth surface. The drastic improvement of iron loss with decreasing surface roughness was mainly due to the decrease in hysteresis loss. According to the analysis of the iron loss and surface roughness of the ribbons, it was considered that gentle and large undulations of the ribbon surface did not prevent domain wall from moving, but steep and small irregularities such as air pockets pinned domain wall. These behavior seems to be caused by the difference of mechanism of domain wall pinning in these two amorphous alloys.