Some calorimetric investigations of the role of electrons in superconductivity and magnetism

Thesis. The heat capacity of the system (La,Ce)Al//sub 2/ for 0.0, 0.193, 0.64, and 0.906 at.% Ce has been measured between approximately 0.06 and 22 K and in magnetic fields up to 38 kOe. In the normal state, there is R1n2 entropy associated wtih the Ce spin system and this entropy is removed in the formation of the spin-compensated state. The nonmal state Kondo temperature is 0.42 K. The three more-dilute samples exhibit supenconductivity but cannot be described by the Bardeen - Cooper -- Schrieffer on Abrlkosov -Gor'kov theories. Significant low-energy excitations are evident in the superconducting state and they may be associated with quasibound states deep in the energy gap of the pure superconductor. Fon the 0.193 at.% Ce alloy in the superconducting state the characteristic temperature associated with Ce-spin ordering in the nonmal state is reduced by an estimated order of magnitude. For the 0.64 at.% Ce alloy a small, broadened superconducting anomaly appears in the heat capacity above 1 K, however, no anomaly that could be interpreted as a broadened discontinuity was found at the magnetically-detected transition back into the normal state at lower temperatures. The heat capacities of five samples of alpha -U have been measured between approximately 0.1 and 2 K at zero pressure. The four polycrystalline samples exhibited broad, bulk superconducting transitions. The gamma -values and the smearing of the superconducting transitions are sensitive to grain size--the small-grained samples had the highest gamma -values and the broadest superconducting transitions. A single crystal had the lowest gamma value and appeared to be beginning to enter the superconducting state below 0.25 K. The shape of the heat capacity anomaly near Tc for the large-grained polycrystal indicates that alpha -U is a BCS superconductor and, hence, local moments and pair-breaking mechanisms do not play a role in its superconductivity. The known pressure enhancement of Tc is partially attributed to a density-of- states effect and partially to a reduction of the pairweakening Coulomb repulsion as the narrow, f-like hybrid band broadens under pressure. The heat capacity of SmS in the insulating and metallic phases has been measured between approximately 0.3 and 20 K. The entropy difference clearly shows the demagnetization of the 4f electrons in the metallic phase. (auth