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

Influence of surface roughness on magnetic properties of Fe₇₈ Si₉B₁₃ and Fe₇₈Si₁₄B ₈ amorphous alloy ribbons was investigated. Magnetic induction in an external field of 800 A/m, B₈ of Fe₇₈ Si₉B₁₃ ribbon increased slightly with decreasing surface roughness, while iron loss W_13/50, at 1.3 T 50 Hz excitation, remained almost at the same level. In Fe₇₈Si₁₄B₈ amorphous alloy, however, quite different behaviors were observed. Both B₈ and W_13/50 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 a 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 the domain wall from moving, but steep and small irregularities such as air pockets pinned the domain wall. This behavior seems to be caused by the different mechanism of domain wall pinning in these two amorphous alloys