Magnetic and Electronic Correlations in Rare Earth Intermetallic Compounds
Stavinoha, Macy L
Doctor of Philosophy
Magnetic and electronic correlations form the framework of physical properties observed in rare earth-based intermetallic compounds. Rare earth ions (La-Lu) can host a variety of behaviors including the Kondo effect, crystal electric field splitting, long-range magnetic order, and valence fluctuations whose combined effects determine the ground state magnetic and electronic properties of the host intermetallic compound. In solid state chemistry and condensed matter physics disciplines, physical properties can be traced through structural families where these behaviors are common to the crystallographic arrangement of the compound. When changes in the physical properties are correlated with small changes in the chemical composition or crystallographic structure of the compound, this provides a route to study and tune the underlying quantum mechanical interactions responsible for unusual or useful characteristics of these materials. In this thesis, I will report the discovery of two new intermetallic compounds YbIr3Si7 and YbIr3Ge7 and two new substitutional series Eu(Ga1-xAlx)4 and Eu1-xAxGa4. The isostructural analogs YbIr3Si7 and YbIr3Ge7 differ greatly in their physical properties, and each compound is unique in its own respect. YbIr3Si7 shows a combination of behaviors that has not been reported in any other compound, including Kondo correlations, insulator-like resistivity, long-range magnetic order, and the onset of conductive surface states at low temperature. YbIr3Ge7, however, is a rare Kondo lattice ferromagnet and the first of which to crystallize in a rhombohedral crystal structure. In contrast, EuGa4 is an antiferromagnetic compound with a ubiquitous tetragonal crystal structure. Small changes in the magnetic Eu sublattice or the nonmagnetic Ga sublattice can introduce unexpected changes in the observed physical properties of the system. Here, Al substitution in the Ga sublattice to produce the single crystal series Eu(Ga1-xAlx)4 results in nonlinear changes to the magnetic ordering temperature and the presence of ferromagnetic correlations, despite the similar size and electronic con figuration of Al and Ga. In contrast, substitution in the magnetic Eu sublattice to form Eu1-xAxGa4 with A = Ca, La, or Sr shows that introducing the smaller Ca ion causes structural distortion, hole doping with La suppresses the ordering temperature rapidly, and Sr substitution slowly suppresses the magnetic order without sacrificing crystal quality.
solid state chemistry; Kondo lattice; Kondo insulator