Surface crystallization and magnetic anisotropy in amorphous Fe40Ni38Mo4B18 ribbons

Abstract

The magnetic anisotropy in amorphous Fe₄₀Ni₃₈Mo₄B₁₈ (METGLAS^R 2826MB) has been studied by the determination of both surface and bulk properties using Mössbauer, x‐ray, and density measurements. The onset of bulk crystallization is preceded by surface crystallization in conjunction with which magnetic anisotropies with easy directions perpendicular and parallel to the ribbon plane develop in the ribbon bulk and surface layers, respectively. It is proposed that the anisotropies, also observed for other amorphous ribbons, originate from compressive and tensile stresses appearing in the bulk portion and surface layers, respectively, as a result of the formation of higher‐density crystalline surface‐layers. The compressive and tensile stresses produce the perpendicular and parallel anisotropies in the ribbon bulk and surface layers, respectively, through positive magnetostriction.