We have discovered a new heavy-fermion system, CeCu6, with a large susceptibility (=0.027 emu/mole G at 1.5 K) and a large, temperature-dependent specific heat below 10 K that is 840 mJ/mole K2 at 1.8 K and extrapolates to 1.6 J/mole K2 at T=0 in analogy with CeAl3. High-field specific-heat measurements agree almost perfectly with a narrow-band picture first proposed for UBe13. © 1984 The American Physical Society.

A pulse-heating method for measuring specific heat and electrical resistivity to high temperatures is described. This technique can be used for electrically conductive materials from room temperature to near 1300 K. As an example of this method, measurements of zirconium are presented.

The compounds UAl2 and UPt3 are thought to exhibit ferromagnetic spin fluctuations. We have measured the electrical resistance of both materials to over 1000 K at zero pressure and from room temperature to 1 K at pressures up to 18 kbar. The primary effect of pressure is to reduce the lowtemperature slope RT and thus shift the inflection point in the resistance to higher temperatures. We interpret these observations as arising from an increase in the spin-fluctuation temperature Ts with increasing pressure. Using a Fermi-liquid description of these materials, we calculate the pressure dependence of the T=0 susceptibility from the pressure dependence of Ts. We also find that the temperature-dependent resistance at various fixed pressures scales as TTs(P) over a remarkably large temperature interval. © 1984 The American Physical Society.

The compound UAl2 exhibits ferromagnetic spin fluctuations at low temperatures. When 15 at.% La is substituted for U in UAl2, we find the low-temperature magnetic susceptibility increases by more than a factor of 2. We have also measured specific heat on this sample at low temperatures. We find that the electronic density of states has increased by 60% and the spin-fluctuation contribution has increased by a factor of 2. We conclude from these measurements that the Stoner enhancement factor has increased by 30% and the spin-fluctuation temperature has increased by 50% as compared with UAl2. In addition, we have measured the electrical resistivity of U0.85La0.15Al2. We find the residual resistivity to be approximately an order of magnitude larger than that of UAl2. We attribute this effect to the breaking of UU bonds by the La atoms. © 1983 The American Physical Society.

We have prepared single crystals of NpBe13, Np0.68U0.32Be13, and PuBe13 and measured their resistivity, susceptibility, and specific heat down to low temperatures. NpBe13 has an itinerant-electron magnetic transition at 3.4 K, with a large temperature-dependent specific heat above this transition that is quite similar to that observed in the heavy-fermion superconductor UBe13 and a (T=0) of approximately 900 mJ/mole K2. PuBe13 may be described as a Kondo-type system, with certain inconsistencies. The data are compared to results for UBe13 and are consistent with a narrow f band at the Fermi energy in UBe13 moving lower in energy with the addition of f electrons in heavier actinide elements to create a Kondo resonance by PuBe13. © 1984 The American Physical Society.

Quasielastic scattering from spin fluctuations has been observed in UPt3 by Raman spectroscopy. The experiments for wave vectors q≈0 show a nearly temperature independent linewidth for 5 K ≤ T ≤ 300 K Complementary to neutron scattering results this establishes the q independence of the spin relaxation rate, indicating the localized nature of the spin fluctuations. A Raman-active phonon near 79 cm-1 (10 meV) shows a drastic increase in line-width with decreasing temperature, demonstrating strong electron-phonon coupling. © 1987.

The 5f spectral weight in the heavy-fermion materials UAl2 and UPt3 has been measured by electron spectroscopy, and compared to that in density-functional calculations. The one-electron 5f widths are both too large to account for the enhanced values of the specific-heat coefficient, and too small to account for the measured widths. In the Anderson Hamiltonian, both discrepancies arise from the 5f Coulomb interaction. It is pointed out that an enhanced value does not imply enhanced magnitude of the 5f spectral weight at EF. © 1985 The American Physical Society.