Surface and bulk magnetic anisotropy in amorphous alloys

Magnetic measurements of hysteresis loops and transverse susceptibilities have been done on as-cast iron based amorphous alloys on the surface and in the bulk of the ribbons. Bitter technique has been used to obtain the domain patterns. a-Fe78B13Si9 shows an anisotropy perpendicular to the ribbon plane with maze domain ‘‘island’’ structures. The surface measurements do not detect any difference in behavior compared to the observed bulk properties. a-Fe81.5B14.5Si4 shows different behavior in the surface and in the bulk of the ribbon with a perminvar-type hysteresis loop from the surface and magnetization perpendicular to the ribbon plane with well-aligned closure domains. The analysis of the different magnetic experimental data and selective changes in the internal stresses produced by different treatments support a model of the layered character of the anisotropies in this sample with tensile stresses and in-plane anisotropy in the surface and compressive stresses and anisotropy perpendicular to the ribbon’s surface in the bulk. Finally, a rough calculation shows that the thickness of the surface in-plane anisotropy region is of the order of the surface roughness.