US-Federal Republic of Germany Cooperative Research: Thermodynamics and Short-Range Order in Amorphous Rare Earth - Transition Metal Alloys

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This award supports Professor Frances Hellman, University of California at San Diego, for collaborative research with Dr. Ruediger Bormann of the Institute of Metal Physics, University of Goettingen, Federal Republic of Germany. They are interested in ferri-magnetic amorphous metal alloys derived from rare earth and transition metal elements. Thin films of these alloys possess a large, poorly-understood uni- axial magnetic anisotropy, which may be induced in the short-range order by the growth process. Certain thermodynamic functions control the stability of the amorphous phase relative to the crystalline phases of these thin films. These investigators will prepare thin film samples of several alloys, differing in composition or deposition temperature. They will make extensive thermodynamic measurements (in Germany), in conjunction with magnetic and structural characterization (in California), in order to compare the degree and type of short range order. Dr. Hellman's background is in thin film specific heat measurement and in preparation and magnetic and structural characterization of amorphous rare earth-transition metal alloys. Her German collaborators have unique and extensive experience in calculations of amorphous and crystalline phase free energies, based on measurements of certain thermodynamic properties of amorphous materials (including thin films.) They also have an ultra-high vacuum magnetron sputtering system, dedicated to preparation of high purity amorphous metallic alloys, especially those containing magnetic elements. The question of intermediate and short range order in amorphous magnetic materials and their relationship to the magnetic anisotropy is of basic as well as technological interest. The difficulty of making thermodynamic measurements in amorphous thin films has delayed progress in this area of materials science. This work should contribute to resolving the question of the origin of magnetic anisotropy in amorphous films. It will also help determine the conditions leading to phase separation in certain alloys which are promising magnetic storage materials.