CAREER: Investigation of Spatial and Temporal Scales of Cooperative Spin Clusters in Doped and Undoped Geometrically Frustrated Magnets

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*** Technical Abstract ***This proposal is an investigation of the fundamental aspects of geometrically frustrated magnetic systems using a combination of magnetic and spatially and temporally-resolved optical techniques. An important consequence of frustration is the ability to form spin 'protectorates'-spin clusters that are decoupled from the rest of the system. The specific issues that will be investigated are: (a) Effect of chemical disorder: The formation of isolated spin protectorates is attributed to nucleation around vacancy-related defects in the crystal structure. The effects of intentional lattice distortion induced by chemical disorder (doping) on frustration will be investigated, (b) Dynamics: Spin clusters in frustrated magnets exhibit fluctuations over a broad range of time scales, varying with temperature and disorder. Their ensemble dynamics will be investigated down to picoseconds to follow the onset and development of frustrated behavior, and (c) Correlation length: The cluster size of the protectorates changes substantially as frustration alters the energy landscape and the spin correlation lengths. The formation and evolution of these protectorates will be studied. This research will combine techniques prevalent in distinct fields (optics, magnetism, and low temperature physics) and the results will lead to the understanding of novel spin related phenomena, and the factors that influence them, in complicated cooperative magnets. *** Non-technical Abstract ***Frustration is the inability of a system to reach a unique ground state. It plays an important role in a wide variety of systems, ranging from protein folding to the formation of nanoclusters. An intriguing set of such systems is magnetic compounds with unique lattice symmetries where the magnetic spins are geometrically frustrated. This proposal will bring a new perspective to the study of geometrically frustrated magnetic systems via the investigation of their fundamental aspects using a combination of magnetic and high-resolution optical techniques. Particular emphasis will be given to the measurement of spatial and temporal scales relevant to the onset and development of frustration. The use of optical probes will allow the first direct measurement of spin dynamics in frustrated systems, and will be able to access time and length scales unattainable by any other existing techniques. The results will lead to general insights into the complicated collective behavior observed in frustrated systems that should be applicable to a variety of fields, such as quantum computing and information processing. Since the location of UC Merced at the heart of the Central Valley offers a means to attract and retain underrepresented students to science and technology, this proposal will enhance participation of minority groups, particularly women, in cutting-edge research through the formation of a focused Women in Science and Engineering group. It will also lead to the development of a 'discovery-oriented' laboratory course with special emphasis on topics of condensed matter and nanoscience for both undergraduate and graduate physics curriculum.