Resonant Ultrasound Studies of Complex Chromium and Vanadium Oxide Spinels

摘要现代凝聚态物理学最令人兴奋的主题之一是在日益复杂的材料系统中发现和研究新现象和新形式的秩序。我们提出的计划的目标之一是研究一组称为尖晶石的新型复杂材料的弹性特性（即材料如何响应应变）。这些尖晶石的弹性响应可能相当奇特，我们的研究计划将探索是否可以用最近发展的理论来理解这种行为。研究生将在弹性性能和低温物理领域获得深入的经验，并掌握材料科学的各种技术技能。这项建议包括开展面向高中生的外展活动。将特别努力帮助女学生。技术摘要本研究计划旨在系统地研究一组复杂过渡金属氧化物（TMOs）的弹性响应，我们认为这些氧化物是研究弹性性能的理想选择：铬和钒尖晶石氧化物。具体来说，我们打算研究的化合物具有AB2O4式，其中B阳离子为Cr3+或V3+， A阳离子为Zn2+， Mg2+, Cd2+， Mn2+或Co2+。这些材料在室温下是立方的，只有3个弹性模量。随着材料的冷却，它们都经历了结构和磁相变，这是目前实验和理论研究的热点。相关的物理学包括晶体扭曲以减轻磁挫折（自旋-泰勒效应），t2流形中的轨道有序和自旋-轨道相互作用，以及轨道占用的磁控制。RUS将在2-400 K和高达9特斯拉的磁场中常规使用，以获得弹性模量。将酌情进行脉冲回波测量。固体的弹性响应是材料的一种度量。年代?应变敏感性?不同对称的张力。在相变附近，它可以提供有关阶参量与应变耦合的信息。这些知识对于理解复杂TMOs的物理性质是必不可少的。研究生将在弹性性能和低温物理领域获得深入的经验，并掌握材料科学的各种技术技能。这项建议包括开展面向高中生的外展活动。将特别努力帮助女学生。

NON-TECHNICAL ABSTRACTOne of the most exciting themes of modern condensed matter physics is the discovery and investigation of novel phenomena and new forms of order in materials systems of ever increasing complexity. It is one of the goals of our proposed program to study the elastic properties (i.e. how a material responds to strain) of a set of novel, complex materials called spinels. The elastic response of these spinels can be quite exotic, and our research program will explore if the behavior can be understood with recently developed theories. Graduate students will gain in-depth experience in the field of elastic properties and low temperature physics, and will acquire skills in various techniques in materials science. This proposal includes the development of outreach activities to high-school students. Special efforts will be made to reach female students.TECHNICAL ABSTRACTThis research program is designed to systematically study the elastic response of a set of complex transition metal oxides (TMOs) that we believe are ideal for elastic property studies: chromium and vanadium spinel oxides. Specifically, the compounds we intend to study have the formula AB2O4, where the B cation is Cr3+ or V3+ and the A cation is Zn2+, Mg2+, Cd2+, Mn2+, or Co2+. These materials are cubic at room temperature, and have only 3 elastic moduli. As the materials are cooled, they all undergo structural and magnetic phase transitions that are currently the subject of intense experimental and theoretical interest. The relevant physics involves crystalline distortions to relieve magnetic frustration (the spin-Teller effect), orbital ordering and spin-orbit interactions in a t2g manifold, and magnetic control of orbital occupation. RUS will be used routinely from 2-400 K and in magnetic fields up to 9 Tesla to obtain the elastic moduli. Pulse-echo measurements will be performed as appropriate. The elastic response of a solid is a measure of the material?s ?strain susceptibility? to strains of different symmetries. Near phase transitions, it can provide information about the coupling of the order parameter to strain. This knowledge is indispensable for understanding the physics of complex TMOs. Graduate students will gain in-depth experience in the field of elastic properties and low temperature physics, and will acquire skills in various techniques in materials science. This proposal includes the development of outreach activities to high-school students. Special efforts will be made to reach female students.