http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Transport and magnetic properties of RTX and related compounds
Physical properties of RTX compounds (R = Rare earth, T = Transition metal and X = main group element from B, C or N group) compounds have been studied by means of electrical resistivity, heat capacity, dc magnetization and NMR. Searching for new magnetic materials is always an interesting topic from both a technological and basic research prospective; it is even more interesting when unusual magnetic phases are observed. Ternary intermetallic plumbides are interesting because of their unconventional magnetic ordering and variety of multiple magnetic transitions. Crystalline electric fields (CEF) also strongly effect the magnetic properties of these intermetallics. To understand the phase transitions, CEF effects, and magnetic interactions, a systematic study of the RNiPb, R₂Ni₂Pb, R₅NiPb₃ and RCuGe systems were conducted. Among the results for NdNiPb a single antiferromagnetic transition was found at 3.5K, while the superconductivity found in some ingots of this material was shown not to correspond to a bulk behavior for this phase. Nd₂Ni₂Pb was shown to have a canted zero field magnetic structure with a low temperature metamagnetic transition 3 T. In NdCuGe, a 3K AF transition was found along with a corresponding magnon contribution to the specific heat and magnetic and thermodynamic behavior from which the detailed CEF configuration was obtained. In a series of measurements on recently-synthesized R₅NiPb₃ (R=Ce, Nd, Gd), for Ce₅NiPb₃ a transition at 48 K was found, which was confirmed to be ferromagnetic character from field dependent heat capacity and Curie-Weiss susceptibility. Nd₅NiPb₃ exhibits two transitions, an antiferromagnetic transition at 42 K and an apparently weak ferromagnetic canting transition at 8 K. For Gd₅NiPb₃, a ferro- or ferrimagnetic transition was found at 68 K. For the Ce and Nd materials metamagnetism was also observed at low temperatures. In addition, very large metallic type [gamma] terms were found in the specific heat, as well as a reduced value of the magnetic entropy, for all three systems. These results imply a lack of ordering for one of the two in-equivalent chains in these materials. This is discussed in terms of possible geometrical frustration on one of the spin chains.
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Doctor of Philosophy Texas A&M University 2008 http://hdl.handle.net/1969.1/ETD-TAMU-3227