From measurements of the electrical resistance of heavy-fermion CeCu6 subjected to hydrostatic pressures, we infer a continuous pressure-induced transition from Kondo-lattice to more strongly mixed-valence behavior. The resistance is found to scale over an appreciable temperature interval with a pressure-dependent characteristic temperature that reflects this transition. Similarities in the resistive behaviors of CeCu6 and CeAl3 are discussed. © 1985 The American Physical Society.

The properties of Cu-flux-grown UCu2Si2 were discussed. The crystals of UCu2Si2 were grown by slow cooling of dilute solutions of molten Cu containing U and Si in the stoichiometric ratio 1:2. Magnetization measurements were performed for 2K ≤T≤ 350K using a commercial SQUID magnetometer. It was found that single crystals of UCu2Si2 grown from Cu flux have a 50 K antiferromagnetic transition below the 100 K ferromagnetic transition.

Ambient pressure characteristics of heavy-fermion compounds, such as the ratio of the low temperature magnetic susceptibility to the electronic specific heat coefficient γ and a simple relationship between the T2-coefficient of resistivity and γ2, suggest that a single-energy scale T0 dictates the physics of these materials. Such is the case for Kondo-impurity systems to which heavy-fermions are related. We consider the consequences of assuming that the electronic free energy is given by a universal function of T/T0(V) where V is the molar volume. We show that volume-dependent magnetic susceptibility, specific heat and electrical resistivity of some heavy-fermion compounds scale as T/T0(V), at least over a range in pressures and temperatures. A further consequence of the principle assumption is that Gruneisen parameters defined as ∂ln X/∂ln V, where X is some physical property, should be identical for all properties and equal to that determined from electronic contributions to the volume-thermal expansion coefficient and specific heat. In several materials, this equality holds, at least approximately. Although evidence is found for single-energy scaling in heavy-fermion materials, we cannot conclude unambiguously that the basic assumption is correct in detail. © 1994 Plenum Publishing Corporation.

The large γ of heavy-electron materials is predominantly a single-ion effect: γ α 1 TK. The most interesting physical effects occur in the low-temperature coherent state of a chemically ordered lattice of these ions. The large-γ state can be strongly quenched by magnetic order, and we argue that this effect is more pronounced for Ce than U materials. We discuss recent work in this light, and address the interesting possibility of heavy-electron materials in which charge fluctuation effects may be important. © 1988.

Pressure-dependent electrical resistivity and ac-calorimetry measurements on single crystals of the heavy-fermion antiferromagnet U(2)Zn(17) at pressures to 5.5 GPa reveal that the low temperature magnetic order changes above ∼3 GPa. The Neél temperature (T(N) = 9.7 K at ambient pressure) decreases slowly for pressures below 3 GPa, but above this pressure a new magnetic state develops at T(M)≈8.7 K. This magnetic phase becomes more stable with pressure increase (dT(M)/dP = 1 K GPa(-1), T(M) = 10.5 K at 5.3 GPa). The heavy-electron state in U(2)Zn(17) is robust against pressure--the electronic specific heat coefficient γ≈0.4 J mol(-1) K(-2) is nearly pressure independent for both magnetic phases. Magnetic ac-susceptibility measurements show that the pressure-induced state is not ferromagnetic.

Magnetic ordering at 2.0 K is inferred from resistivity measurements on URh2Ge2. The transition temperature is not sensitive to applied pressure, suggesting stability of the magnetic moment of uranium in this material. © 1985.

The application of modest pressures p to rare-earth and actinide-based heavy-electron / Kondo-lattice materials produces significant changes in both their temperature dependent electrical resistivity ρ{variant} and electronic specific heat γ. For a given compound, γ(p, T=0) appears to scale inversely with a characteristic temperature associated with features in ρ{variant}(p, T). These changes can be understood as arising from the strongly volume-dependent competition of interactions giving rise to the heavy-mass ground state. Similar behavior also may be found in transition-metal compounds, e.g., MnSi. © 1989.

We have studied the response of heavy-fermion magnets UCd11, U2Zn17 and UAgCu4 to hydrostatic pressures exceeding 17 kbar through temperature-dependent electrical resistance measurements. Results for U2Zn17 and UAgCu4 can be understood in terms of competing Kondo and RKKY interactions. UCd11 exhibits two new phase transitions induced by pressure. © 1986.

We review the crystal chemical, electronic, magnetic and superconducting properties of La2CuO4 and related planar-cuprate materials, with emphasis on single-crystal results. Although magnetism due to divalent copper ions clearly is evident in nonsuperconducting crystals, experiments do not reveal any direct relationship between localized copper spins and high temperature superconductivity. We also indicate areas where important information is lacking for our understanding of these materials. © 1989.

We argue that the materials which appear to maximize the superconducting transition temperature can be regarded as living at the interface between chemistry and physics.