Resonant Ultrasound Studies of Complex Chromium and Vanadium Oxide Spinels

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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.