Effect of surface features of amorphous alloys on magnetic behavior

Air pockets were found on amorphous ribbons of Fe-Bi-Si and Fe-B-Si-C with different sizes, shapes, and orientations due to differences in processing conditions. The coercivity decreased and the magnetization in low fields increased as the size of the air pockets decreased. The coercivity was always higher and the magnetization lower for air pockets oriented parallel to the ribbon length. The same trends remained after stress relief annealing. Applications of tensile stress produced changes correlated to differences in air pocket size and orientation. The 60 Hz coercivity, loss, and maximum drive field exhibited the same trends as the dc coercivity with changes in air pocket size and orientation. The difference between Hc(60 Hz) and Hc(dc) increased with decrease in air pocket size. It is concluded that the air pockets influence the magnetic properties of ribbon by providing wall pinning sites which control the motion of walls present during magnetization reversal and by providing regions in the ribbon with a misorientation in the easy axis.