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

小行星9527357 该提议涉及对一些具有短程交换相互作用的不寻常的纯、稀和混合磁系统的磁行为，特别是与磁相变有关的磁行为的详细研究。纯材料很有趣，因为其中四个是一个新的3d过渡金属二氯化物一水合物家族的成员，其中两个已经观察到类似自旋玻璃的行为;另一个是铁磁性的，是罕见普适类的潜在成员;另外两个表现出非常大的零场分裂。绝缘材料中自旋玻璃行为的研究具有特别的意义和重要性，并且要研究的几个混合磁性系统可以表现出自旋玻璃相。其中之一是潜在的三维XY绝缘自旋玻璃。3D-XY铁磁体的稀释行为本身就是一个重要的问题。其中两个混合系统是三元的，即它们含有三种不同的磁性成分或两种磁性和一种抗磁性。在绝缘材料中，这种系统实际上是未经研究的。混合磁体将包含竞争交换相互作用、竞争各向异性、不同自旋值或这些的某种组合。磁相图的测定，显示有序化温度对组成和相稳定区域的依赖性，是这项工作的一个主要目标。某些理论上预测的相图类型还有待观察。 本研究包括对一些具有短程交换作用的不寻常的纯磁、稀磁和混合磁系统的磁行为的详细研究。纯材料是有趣的，因为某些成员表现出自旋玻璃般的行为，是铁磁性的，或者它们表现出非常大的零场分裂。各种各样的系统被提出来研究，因为几种不同的现象是感兴趣的。实验方法主要包括对多晶和单晶样品的变温、变场磁化测量。 还计划在中子衍射和散射、高场磁化和长时间热释光磁化测量方面开展合作工作。拟议的工作将对部门的研究环境产生重大影响，特别是在夏季和学年期间为本科生提供的研究机会。这些经验是他们科学教育的重要组成部分，也是为以后的科学工作做好宝贵准备。

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.