Local symmetries and structural distortions in amorphous ferromagnetic metals: A study of their contributions to the aftereffect of the magnetic permeability

Abstract

The nature of the magnetic-permeability aftereffects observed in amorphous ferromagnets is investigated on a microscopic basis. The present calculation is an improvement of a recent magneto- strictive approach to the problem of magnetic aftereffects in metallic glasses. The theory is based on the analysis of the fluctuation of the local magnetic anisotropy energy induced, at each site of a random close-packed structure, by the distortion of the first shell of magnetic neighbors. The magnetic aftereffect originates from a directional ordering of shear-stress defects interacting with the spontaneous magnetization via this energy. The experimental aftereffect data are coherently interpreted by this picture. The aftereffect is also shown to be related to the average value of a local order parameter, giving information on the degree of bound-orientational order of the structure. Such a result underlines the close connection existing between magnetic aftereffects and local symmetries and distortions of a close packing of spheres. The new expression for the permeability aftereffect is discussed on the basis of a set of experimental results taken on as-cast and annealed ribbons of amorphous alloys.