C. A. Luengo

Superconducting and normal state properties of Li1+x Ti2?x O4 spinel compounds. II. Low-temperature heat capacity

Heat capacity data are reported which confirm as a bulk effect the previously reported superconductivity in LiTi2O4. These data also establish LiTi2O4 as a weak couplingd-band superconductor with superconducting state properties well described by the Bardeen—Cooper—Schrieffer theory of superconductivity. The properties of LiTi2O4 are compared with those of other superconducting spinel compounds, and the composition dependence ofTc for Li1+xTi2−xO4 is discussed. The disappearance of superconductivity forx≳0.1 was found to be correlated with a rapid decrease in the normal-state linear heat capacity coefficient.

Heat capacity of the superconducting Kondo system (LaCe)Al2

Abstract Heat capacity measurements between 0.07 and 20 K and 0 and 38 kOe are reported for the system ( La Ce)Al2. Normal state measurements show that the crystal-field ground state of the Ce ion is a doublet and reveal a characteristic Kondo anomaly in zero magnetic field. In the superconducting state there is evidence for an impurity band at low energies within the gap, and for a second order transition at the lower critical temperature Tc2.

Demagnetization of Ce impurities in superconducting (La, Th)Ce alloys: Specific heat results

Detailed measurements of the specific heat jump ΔC at the superconducting transition temperatureTc as a function ofTc are reported for several (La, Th)Ce systems. The measurements document the continuous demagnetization of the Ce impurity ions which proceeds with increasing Th concentration, and provide a critical test of a theory recently developed by Müller-Hartmann and Zittartz for the superconducting behavior of matrix-impurity systems which simultaneously exhibit both superconductivity and the Kondo effect.

Magnon heat capacity, magnon magnetization and magnetic entropy of the weak ferromagnet UPt

Abstract A T 3 2 contribution to both the heat capacity and the saturation magnetization of the weakly ferromagnetic compound UPt reveals the existence of spin waves in the ferromagnetic state below the Curie temperature of 30 K. The entropy of ordering, extracted from calorimetric data on UPt and the isostructural nonmagnetic compound ThPt, is much smaller than the degeneracy entropy expected from the p ss″ e 5f3 (U3+) or 5f2(U4+) ionic configuration, but much larger that the value observed in itinerant ferromagnets.

Specific heat of superconducting Th, Sc and Th, Y alloys with Ce impurities

Abstract Measurements of the specific heat jump ΔC at the superconducting critical temperature Tc on ( Th, Sc )Ce and ( Th, Y )Ce Ce impurity, solid solution alloy systems indicate that the former systems obey the BCS law of corresponding states (LCS) characteristic of superconductors with non-magnetic impurities while the latter systems present deviations from the LCS linear relation between reduced parameters which are attributed to the development of localized moments at the Ce ions as the Y concentration increases.

Calorimetric study of the magnetization of Ce impurities in superconducting Th-Y and Th-Sc alloys

Specific heat measurements are reported in detail for the Ce impurity in the superconducting matrix systems Th65Sc35Ce, Th80Y20Ce, and Th65Y35Ce. The variation of the specific heat jump ΔC at the superconducting transition temperature Tc is indicative of the magnetic nature of an impurity. For Th65Y35Ce a departure is found from the BCS law of corresponding states predicted for a nonmagnetic impurity. This departure is correlated with that observed for (La, Th)Ce systems and related to ΔT c/n (initial slope of Tcvs. n) and Ce effective size (implied by lattice parameter data).

Free energy and thermodynamical critical fieldH c (T) of a superconductor with crystalline-field-split magnetic impurities: (La/itPr)Sn3

An expression for the free energy of a superconductor containing magnetic impurities with crystalline-field-split energy levels is derived. It is used to calculate the thermodynamic critical fieldHc(T) of(LaPr)Sn3. ExperimentallyHc(T) is determined from measurements of the heat capacity of(LaPr)Sn3 in the normal and superconducting states. The two results are in general agreement and demonstrate the role of the inelastic pair-breaking mechanism in this nonmagnetic ground-state system.