The influence of pressure P on the superconducting transition temperature Tc has been determined for the (U1-xThx)Be13 system. The magnitude of dTcdP increases by a factor of 3 for x>1.7% where an increase of Tc is observed at ambient pressure. The phase diagram of Tc(x) for P=10 kbar shows two distinct regions of superconductivity. © 1986 The American Physical Society.

Gadolinium impurities in UBe13 depress the Tc at an initial rate of -0.40 K/%, while in Th0.029U0.971Be13 the initial rate is only -0.19 K/%. This strongly suggests two different superconducting states. Further data on thorium depressions and critical fields are presented. © 1987.

The temperature T dependence of the upper critical magnetic field Hc2 of the heavy-electron superconductors U1-xThxBe13 (x=0 and 2.9%) doped with various concentrations of Gd has been determined from low-frequency ac magnetic susceptibility measurements in magnetic fields up to 60 kOe. The Hc2(T) curves for U1-xGdxBe13 samples deviate from the Hc2(T) curves of UBe13 near Tc, which is consistant with the depairing of superconducting electrons via the Zeeman interaction between the spins of the superconducting electrons and the exchange field associated with the Gd spins. This suggests that UBe13 exhibits singlet superconductivity. In contrast, the Hc2(T) curves for (U0.97Th0.03)Be13 doped with Gd scale with Hc2(T) of pure (U0.97Th0.03)Be13 and do not reflect superconducting depairing by the Gd ions. These results are consistent with either strong spin-orbit scattering due to the presence of Th in UBe13, or to a qualitatively different type of superconductivity involving triplet spin pairing in (U0.97Th0.03)Be13. Measurements of the temperature dependence of Hc2 for U1-xRxBe13 compounds where R=La, Lu, and Ce for various compositions x as well as U0.985R0.015Be13 compounds for R=Tb, Dy, Ho, and Er are also presented and compared with the Gd-doped UBe13 system. The results of low-temperature specific-heat measurements of UBe13 doped with various concentrations of Gd are also discussed. © 1991 The American Physical Society.

The temperature dependence of the upper critical magnetic field Hc2(T) of the heavy-fermion superconductor UBe13 was determined resistively. The magnitude of the initial slope of Hc2(T).

The longitudinal and transverse upper critical magnetic fields Hc2 and Hc2 as a function of temperature T of a single-crystal specimen of the heavy-fermion superconductor UPt3 were measured resistively with the current flowing along the hexagonal c axis. The slope of the linear part of the Hc2 (T) curve near the superconducting transition temperature Tc=0.52 K equals 63 kOe/K, from which a zero-temperature superconducting coherence length 3/401/4120 can be inferred. An analysis using previously reported specific-heat data yields an effective mass ~200 times the free-electron mass and a value of 3/401/4170. The electrical resistivity between Tc and 8 K varies as Tn with n=1.6±0.1. © 1984 The American Physical Society.

Measurements of the ac electrical resistance as a function of temperature and applied magnetic field R(T,H) were made for various compositions x≲0.03 in the mixed binary system (U1-xThx)Be13. All samples within this range of x exhibit heavy Fermion superconductivity with a superconducting transition temperature Tc that is rapidly suppressed by the substitution of Th for U. The shape of the upper critical field curve Hc2(T) determined from the R(T,H) data is similar for all compositions with a very large initial slope (-dH c2/dT)Tc.

We present data on the magnetic and superconducting properties of rare earth osmium stannides. The compounds of Tb and Ho are superconducting only, those of Er and Tm are reentrant superconductors, and those of Gd and Dy appear to exhibit some type of short range magnetic order at low temperatures. © 1982.

The current understanding of the superconductivity of heavy-electron uranium compounds is reviewed. Both the pairing and the mechanism appear to have been established as unusual in UPt3 and UBe13. Small-moment magnetic ordering is now known to coexist with superconductivity in URu2Si2 and UPt3. The understanding of the properties of UBe13 may be viewed as the central problem in heavy-electron physics. © 1988, Elsevier Science Publishers B.V.. All rights reserved.