New Magnetoresistant Oxides of Mixed 3d/4d/5d Transition Metals

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The objective of this proposal is to investigate a new series of mixed oxides containing primarily 4d and 5d transition metal cations, with additional magnetic impurities from the 3d transition-metal series. Our recent work on Fe3+-doped SrRuO3, CaRuO3, and Sr2RuO4 has revealed a very large magnetoresistance that was not previously known to exist in any ruthenate. More broadly, these results suggest that large local moments can arise in conducting oxides, and such materials can be exploited to gain new functionality and new understanding of ceramics. Our strategy is to use strongly magnetic 3d impurities to polarize the narrow 4d/5d conduction bands of the host, so that large electronic and magnetic responses are induced. The magnetic states and the energies of the 3d impurities will be systematically varied, by distorting the crystal structure and changing the composition, to match with those of the conduction bands of the host 4d/5d metals. Cation ordering will also be used as a tool to direct the crossover from spin-frustrated, intragrain magnetoresistance behavior to ferrimagnetic, intergrain magnetoresistance behavior. Single crystals, epitaxial thin films and polycrystals will be compared to determine the role of the grain-boundary effect, while first-principles calculations of model, ordered mixed-metal oxides will be made to benchmark the electronic energy levels of disparate cation d-orbitals. Meanwhile, synchrotron radiation will be utilized to determine the structures and electronic states of these compounds. Our educational program will offer training to undergraduates and high school teachers to provide them with laboratory and research experience. Further outreach to industry will be made through collaborative, synergistic, and exploratory research with a start-up company.Ceramic magnets are typically insulators. This project will explore new magnetic ceramics that become better conductors under a magnetic field. These materials have not been studied in the past but are becoming interesting because of the prospect of spintronic devices. Compared to conventional electronic devices, spintronic devices process more information by detecting and transmitting not only the charge but also the spin of electrons.