Local and Non-local Magnetic Moments in Semiconductors

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This individual investigator award will provide support for a project that will investigate the effect of adding magnetic moments to semiconductors. Amorphous Si, Ge, and C doped with magnetic ions such as rare earth elements and Mn will be prepared and their electronic, magnetic, thermodynamic, and structural properties measured. The influence of the phonon stiffness and the semiconductor band gap on these properties will be determined. The interaction between these added local moments and the spontaneous moments formed at the Metal-Insulator transition as electrons localize will be studied. The research will provide a phenomenological underpinning for a microscopic model for the three dimensional Metal-Insulator transition, and an understanding of the effect on both transport and magnetic properties of introducing local magnetic moments into a semiconductor. The project will provide research training and education for two graduate students and an estimated 5-6 undergraduates, including exposure to industry through the PI's connections with the Center for Magnetic Recording Research at UCSD and to two National Labs, the National High Magnetic Field Lab and Los Alamos.Magnetic moments play a crucial role in many materials (e.g. the high Tc superconductors and the colossal magnetoresistance manganites). It is known that adding magnetic moments to semiconductors produces effects that are extremely large, but these effects are not well understood. In particular the change in the electrical resistance when such a material is placed in a magnetic field (magnetoresistance) can be enormous. This project will investigate the effect of adding magnetic moments to semiconductors. Samples of amorphous Si, Ge, and C doped with magnetic ions such as rare earth elements and Mn will be prepared. Their electronic, magnetic, thermodynamic, and structural properties will be measured over a wide range of temperature, magnetic field, and doping levels. The research will attempt to determine the principles governing the large effect of magnetic moments in amorphous semiconductors. An increased understanding of these effects may point the way to making the very large magnetoresistance of use to the developing spin electronics technology. In addition this research may increase our understanding of why magnetic moments play such a crucial role in other materials of current interest. The project will provide research training and education for two graduate students and an estimated 5-6 undergraduates, including providing them with an exposure to industry and to the national labs through the PI's collaborations. Thus, they will be well prepared for future careers in academia, or industrial or government laboratories.