Vapor-deposition-induced magnetic anisotropy in amorphous RE-TM alloys (invited) (abstract)

Abstract

Macroscopic anisotropy may be induced in amorphous materials by either preparation or subsequent annealing under appropriate conditions. Large, macroscopic magnetic anisotropy is observed in amorphous rare earth–transition metal (a-RE-TM) alloys produced by vapor deposition. The vapor deposition process inherently contains characteristic directions about which an anisotropy can occur. These include the substrate, incident atomic beams, and magnetic or electric fields at the surface during growth. These intrinsic directions combine to produce effects such as columnar microstructure, stress and strains, pair ordering in alloys, and nonperpendicular film growth directions. All of these structural effects potentially can produce magnetic anisotropy. The presence of the localized nonspherical f-electron nature of the RE ions causes a large local magnetic anisotropy; a macroscopic structural anisotropy can then cause a coherence in the directions of the local anisotropy axes, thereby producing a large macroscopic magnetic anisotropy. When the induced structural anisotropy is local in nature, it can be subtle and difficult to resolve, even though the resultant magnetic anisotropy itself is easily measured. We have used the magnetic anisotropy directly to monitor the effects of the important parameters of vapor deposition growth (e.g., substrate temperature, alloy composition, state of stress during growth, incident atomic beam angles) in order to understand what fundamental growth process is causing the anisotropy. Both the local anisotropy (as reflected by the high-field magnetic susceptibility) and the macroscopic anisotropy has been analyzed. I will present results which show that the dominant contribution to the macroscopic anisotropy in a-Tb-Fe is an amorphous phase texturing at the surface during the growth, due to minimization of the free energy of the surface. This effect is analogous to well-known effects in growth of crystalline materials. A secondary contribution due to stress plus magnetostriction is also observed.