Investigation of Superconductivity and Physical Properties of Intermetallic
Compounds: MoN, Mo3Sb7, MgCNi3 and Transition Metal Diborides
In this dissertation work, I report on the interesting results of our detailed investigations of the synthesis, structural, electrical and magnetic characterization of three different classes of intermetallic systems. Mo3Sb7 wires, thin films and microfibers exhibit the highest Tc ~ 8 K, which is substantially higher than the 2.2 K reported for the single crystal and powder of Mo3Sb7. The suppression of the spin fluctuations in Mo3Sb7 is evident by the absence of a parabolic dependence of magnetic susceptibility at 1 T. MoN wires, thin films and coated microfibers have Tc ~13 K which is consistent with the values reported in the literature. To my knowledge, for the first time we report on the magnetotransport and critical current measurements in MoN and Mo3Sb7 in these forms. We show (1 - (T/Tc)2)3/2 dependence of the critical current density of MoN- and Mo3Sb7-coated microfibers near the transition temperature, Tc. The extrapolated values of the critical current density to zero temperature for the MoN- and Mo3Sb7-coated fibers are Jc(0) = 1.66 x 108 A/cm2 and Jc(0) = 7.7 x 105 A/cm2 , respectively. The results of magnetic susceptibility and transport properties measurements of Mg1-xBexCNi3 and Mg1-xLixCNi3 for x = 0 to 0.2 showed a very small change in Tc and Hc2 due to Be and Li doping in MgCNi3. The heat treatment of the carbon deficient samples MgCxNi3 for 2 h in N gas improved the superconductivity of the compounds. In MgC0.7Ni3, the superconductivity re-appeared after the treatment. Single crystals and polycrystalline samples of VB2 and other transition metal diborides were synthesized. Cr1-xVxB2 are paramagnetic for x > 0.23, and no superconductivity is observed above 1.8 K. We also present the results of magnetotransport and de Haasvan Alphen (dHvA) measurements on high quality single crystals of VB2 grown from a molten aluminum flux. At low temperature the magnetoresistance of VB2 is very large (?1100%) and is found to be extremely sensitive to sample quality (RRR value).
Advisor:David P Young; Phillip W Adams; Dana Browne; Julia Chan; Christopher White
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:05/16/2008