Abstract
Abstract The crystal structure and symmetry of crystalline magnetic materials determine the nature of their magnetic anisotropy including the direction of the easy axis of magnetization. In amorphous metallic alloys, particularly those containing non S-state rare earth ions, the coupling to the immediate environment gives rise to a local magnetic anisotropy (RMA) which reflects the real space structure of such systems. This article is an attempt to review The origin and consequences of these local couplings in systems which lack long range periodic order. The paper begins with a description of the structure of amorphous metals and its similarity to the dense random packing of hard spheres (DRPHS), a mode ideally suited for detailed computer simulation. The experimental data are presented with a view to assessing the effects of RMA on the magnetic properties of amorphous rare earth alloys. The main emphasis of the text is a detailed examination of the various theoretical models for RMA which have been introduced either in model calculations or in conjuction with computer generated clusters. Magnetization, Mossbauer and specific heat calculations in the molecular field approximation are presented and related to data for both ferromagnetic rare earth-noble metal and ferromagnetic rare earth-transition metal alloys. It is shown that this approximation works well at high magnetic fields and low temperatures and also provides a good description of the hysteresis effects. On the other hand, the remanent state of these alloys often appears to a be a spin glass-like state which cannot be described by the molecular field equations but can be found in Monte Carlo simulations based on the RMA. Finally, the spin excitations of systems with RMA are analyzed within a random phase approximation as well as by a Monte Carlo calculation. The article concludes with an evaluation of the progress to data and an outline of related problems yet outstanding.
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