Magnetism and Phase Transitions of Unusual Pure, Dilute and Mixed Magnets

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9527357 DeFotis This proposal is concerned with the detailed study of magnetic behavior, especially that associated with magnetic phase transitions, of a number of unusual pure, dilute and mixed magnetic systems with short- range exchange interactions. The pure materials are interesting because four of them are members of a new family of 3d transition metal dichloride monohydrates in two of which spin glass- like behavior has already been observed; another is ferromagnetic and a potential member of the rare universality class; and two others exhibit remarkably large zero-field splittings. The study of spin glass behavior in insulating materials is of particular interest and importance, and several of the mixed magnetic systems to be studied could exhibit spin glass phases. One of these is a potential three-dimensional XY insulating spin glass. The behavior of a 3D-XY ferromagnet with dilution is itself an important problem. Two of the mixed systems are ternary in character, i.e, they contain either three different magnetic components or two magnetic and one diamagnetic. Such systems are virtually unstudied among insulating materials. The mixed magnets will contain either competing exchange interactions, competing anisotropies, different spin values, or some combination of these. Determination of magnetic phase diagrams, showing the dependence of ordering temperature on composition and regions of phase stability, is a major objective of this work. Certain theoretically predicted phase diagram types are yet to be observed. %%% This research include a detailed study of magnetic behavior of a number of unusual pure, dilute and mixed magnetic systems with short- range exchange interactions. The pure materials are interesting because certain members exhibit spin glass-like behavior, are ferromagnetic, or they exhibit remarkably large zero-field splittings. A variety of systems are proposed for study because several different phenomena are of interest. Experimenta l methodology consists primarily of variable temperature, variable field magnetization measurements, on polycrystalline and single crystal samples. Collaborative work also is planned for neutron diffraction and scattering, high field magnetization, and very long time thermoremanent magnetization measurements. The proposed work will have a major impact on the departmental research environment, especially in opportunities afforded undergraduates for research during the summer and during the academic year. Such experience is a critical part of their scientific education, and valuable preparation for later scientific work.