G. Weber

Heavy-fermion superconductivity atT c =2K in the antiferromagnet UPd2Al3

UPd2Al3 is a new heavy-fermion superconductor with a recordTc of 2 K. In addition, it shows a transition to long-range antiferromagnetic order atTN=14 K. Its Sommerfeld coefficient is reduced from γp=210mJ/K2 mole in the paramagnetic to γ0=150mJ/K2 mole in the antiferromagnetic phase.

Thermal expansion, sound velocities, specific heat and pressure derivative of Tc in YBa2Cu3O7

We report measurements, between helium and room temperature, of the thermal expansion α(T), sound velocitiesvL(T) andvT(v) and specific heatC(T) of YBa2Cu3O7 samples, all cut from the same sintered pellet. A linear term in α(T) is resolved at low temperatures. It is compared with a corresponding term in the low temperature specific heat and, using the bulk modulus from our sound propagation measurements, a Grüneisen parameter of usual size (1.2±0.4) is derived-in conformity with the possible existence of non-superconducting carriers well belowTc. Longtime drift effects in the length of the sample between 30 K and 60 K point to the vicinity of a structural instability. The Debye temperature derived fromC(T) amounts to about 450 K atT=Tc=91 K and forT→0 approaches 350 K, in agreement with the value deduced fromvL(T) andvT(T). The superconducting transition is indicated by anomalies with idealized discontinuities Δα and ΔC. A thermodynamic relation between Δα and ΔC yields the relative pressure derivative ofTc,tp=Tc−1(∂Tc/∂p)p→0=+(0.7±0.2)·10−7 kbar−1.

Observation of a Schottky Anomaly in the Specific Heat of the Heavy-Fermion Compound UBe13

We present the results of calorimetric measurements of the specific heat in UBe13 and ThBe13 in the temperature range 20 K T 120 K. Combined with earlier results of inelastic neutron scattering, the data allow the extraction of the electronic specific heat ΔC in UBe13. ΔC shows a pronounced peak around 70 K which we interpret as a Schottky anomaly due to crystal-field splitting of a 5f3 ground-state configuration. Our results suggest the existence of highly localized 5f electrons in the heavy-fermion compound UBe13.

Phase transitions in the heavy Fermi-liquid state: CeCu2Si2, UNi2Al3 and UPd2Al3

Abstract We discuss the superconducting and other phase transitions in CeCu 2 Si 2 and UT 2 Al 3 (T: Ni,Pd). For CeCu 2 Si 2 , a novel lattice instability is found to limit the highest T c attainable by appropriate heat treatment. In the UT 2 Al 3 homologs, antiferromagnetism develops at T N = 4.6K (14K) and possibly coexists with heavy-fermion superconductivity below T c = 1K (2K) for T = Ni(Pd).

Crystal-field effects and f-derived specific heats in heavy-fermion compounds

Abstract We discuss experimetal results of calorimetry on heavy-fermion compounds (HFC) with special regard to the f-derived specific heat ΔC . Attention is given to the extraction of Δ C and the uncertainties implied therein. The discussion includes some Ce-based 4f systems but concentrates on U-based 5f HFC. In four of these (UBe 13 , UPt 3 , URu 2 Si 2 , U 2 Zn 17 ) distinct anomalies in Δ C have recently been found in the temperature range between 20 and 100 K which we think are likely to be caused by crystal-field effects thus indicating strong 5f localization.

Specific heat and thermal expansion of CeCu2Si2 at low temperature

Specific-heat and thermal-expansion measurements on CeCu2Si2 samples of varying stoichiometry as well as on dilute (Ce, T)Cu2Si2 alloys (T:Y,La) indicate that the observed suppression of superconductivity in samples with “high” unit-cell volume is associated with a reduction of the Kondo temperature and the occurrence of another cooperative phenomenon, probably magnetic in origin.

Magnetization and specific heat of CeAl3

Abstract Measurements of the high-field dc magnetization and low-field ac susceptibility as well as specific-heat experiments covering almost four decades in temperature characterize CeAl 3 as a “dense Kondo system” with T k ≈ 5 K. From these results, the low-temperature value of the “Wilson ratio”, R (0) = 2.9, is deduced.

AN INELASTIC NEUTRON SCATTERING STUDY ON THE HEAVY FERMION SYSTEMS CeCu2Ge2 AND CeAg2Ge2

An inelastic neutron scattering study is performed on the new magnetically ordered heavy-fermion systems CeCu2Ge2 and CeAg2Ge2. The temperature dependence of the quasielastic line can be interpreted in terms of a Kondo type of behavior. In addition crystalline electric field transition energies are reported.

Specific heats and crystal-field splittings of CeCu2Ge2, CeRu2Ge2 and UBe13

The f-electron contributions to the specific heats of CeCu2Ge2, CeRu2Ge2 and UBe13 were determined and show Schottky anomalies at temperatures between 50 and 250 K. From these the crystal-field splittings are deduced. The specific heat connected with the magnetic phase transition in CeRu2.16Ge2 was measured and a second anomaly observed, which points to a complicated magnetic order.

Transition from Kondo to intermediate valence in Ce1−xYxAl2

Abstract High-temperature specific heat measurements and an extensive study of the thermal-expansion coefficient on Ce 1− x Y x Al 2 reveal for x ⩽ 0.6 trivalent Ce-ions, which are subject to Kondo and crystal-field effects. A continuous transition into an intermediate valent state occurs for higher Y concentrations.