Order from Disorder: Tuning Long-Range Magnetic Ordering by Chemical Doping in Strongly Correlated Intermetallics

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****Technical Abstract****An experimental investigation of the electronic and magnetic ground states in novel intermetallic systems is proposed. Emphasis will focus on the synthesis and characterization of small band-gap semiconductors, including, a series of compounds related to FeGa3 and the alkaline earth and rare earth hexaborides. The properties of these strongly correlated electron materials depend sensitively on parameters such as sample stoichiometry, carrier density, temperature, chemical/physical pressure, and magnetic field. The long-range magnetic order induced by chemical doping in the non-magnetic semiconductor FeGa3 will be studied. A ferromagnetic quantum critical point (FM-QCP) was recently discovered which points toward a novel structural feature driving the criticality - the density of mixed valent Fe-Fe dimer "singlets". Second, this project will investigate the possibility of raising the ferromagnetic ordering temperature in doped Kondo insulators. FeSi is the classic example, and shows similar properties to that of FeGa3. Measurements of the anomalous Hall effect have shown to be an excellent parameter in predicting a material's potential for spintronics applications. Finally, an irradiation study of high quality single crystals of hexaboride materials is proposed in an effort to verify the mechanism of the high-Tc weak ferromagnetism. In this case, the disorder in the system stems from vacancies in the boron sublattice. This experimental research will provide post-doctoral associates, graduate, and undergraduate students with valuable experience and training in the areas of materials synthesis, structural characterization, measurement of physical properties as a function of temperature and magnetic field, and data acquisition and analysis. ****Non-Technical Abstract****This proposed research will focus on the synthesis of materials that possess very unique physical properties. Semiconductors and magnetic materials, for example, are at the heart of many of today's advanced technologies and devices. This project will investigate how intentionally disordering a material, either chemically, or with defects, can result in enhanced physical properties, such as high temperature magnetism. This proposed research program will aid in the understanding of strongly correlated electron systems in general, and may result in new materials for applications, such as in the emerging field of spintronics (spin-based electronics), which could revolutionize the computer memory industry. Post-doctoral associates, graduate, and undergraduate students will gain valuable experience in the areas of materials synthesis, structural characterization, measurement of physical properties, and data acquisition and analysis. A major component of this research project is in materials synthesis, which provides a natural bridge between teaching and research, especially for undergraduates. They are able to make real contributions in a relatively short amount of time, utilizing a variety of solid state physics and chemistry techniques. Furthermore, the synthesis of new materials is vital to the United States remaining competitive in the race for advanced technologies.