Rational design and quantum chemistry of complex itinerant intermetallic magnets: syntheses, crystal structures, magnetic properties and quantum-chemical calculations of new complex borides of the transition metals, M9M`2T18-xT`xB8 (M = Sc, Ti; M` = Mn, F

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This project combines experiment and theory towards the designed preparation and subsequent characterization and thorough understanding of new intermetallic ferromagnets and antiferromagnets. The primary concept involves using a complex metal boride framework with magnetic 3d elements, e.g., Cr, Mn, Fe, Co and Ni, inserted in voits that create magnetic structures with low-dimensional character. These materials will be studied by X-ray and neutron diffraction as well as magnetization experiments to determine atomic and magnetic structures. Theoretical determination of the electronic structures on various models of these structures will provide feedback toward further synthetic efforts of atomic substitutions to create new compounds with targeted magnetic behavior. This effort represents a strong, synergistic coupling of experiment and theory that targets new magnetic materials, and may lead to new materials with unusual bulk magnetic properties due to the potential one-dimensional character of the magnetic exchange. Experimental effort will initiate with potential derivatives of a robust, complex structure type, as found for the newly synthesized compound Ti9Fe2Ru18B8. The new intermetallic series M9M¿2T18-xT¿xB8 (M and T represent metal elements; M¿ specifically indicates a magnetic metal element) will serve as a chemical system in which the numberof valence electrons can be tuned to induce desired magnetic properties. Temperature-dependent structure analyses, neutron diffraction experiments, magnetic measurements and calorimetry will be carried out to characterize these products. Theoretical investigations will start with the simpler tetragonal system, M2M¿T5-xT¿xB2, in which the number of valence electrons varies from 61 to 67 electrons and shows variation in local magnetic behavior, and then evolve to the more complex systems.This project is a close collaboration between solid-state chemistry groups at the Institute of Inorganic Chemistry at RWTH Aachen and the Chemistry Department at Iowa State University (ISU). The Aachen group will extend its present synthetic experience using classical high temperature synthetic routes to synthesize several compounds in this new series, characterize them using diffraction methods and EDX analyses and measure their magnetic properties. Parallel to these synthetic efforts, the ISU group will use electronic structure packages and chemical bonding analyses to understand the electronic and magnetic behavior of these complex phases and predict new synthetic targets for the Aachen group. In addition, the ISU group will carry out temperature-dependent single crystal studies to explore details in structural changes with magnetic behavior. For any ferromagnetic products, calorimetric measurements will also be conducted to explore their magnetocaloric effects, which is important for elucidating possible thermomagnetic applications. Likewise, both groups will clarify the spin structures of the new compounds by experimental (neutron diffraction) and theoretical (spin-polarized supercell calculations) efforts.