The electrical resistivity of YbAgCu4 has been measured at pressures up to 100 kbar and at temperatures between 1 and 300 K. With increasing pressure, the resistivity maximum shifts to lower temperatures and the coherent regime disappears above about 60 kbar. At the highest pressures, a field of 8 T produces a large negative magnetoresistance, roughly equivalent to a negative pressure of 30 kbar. The behavior is consistent with a pressure-induced decrease in the Kondo temperature. © 1994.

A zero-temperature magnetic-nonmagnetic phase boundary is accessed in CeRh2Si2 by application of pressure and in CeRh2−xRuxSi2 at ambient pressure for x ≈ 1.0. A comparison of specific heat and resistivity measurements in the two cases emphasizes the importance of disorder in producing non-Fermi-liquid-like behavior in these as well as in other Ce-based systems. © 1997 American Physical Society.

The electrical resistivity (ρ{variant}) and magnetoresistance of polycrystalline YbAgCu4 have been measured at temperatures between 25 mK and 300 K, and at magnetic fields (B) up to 18 T. The magnetoresistance (ρ{variant}(B) - ρ{variant}(0))/ρ{variant}(0)) is positive at all temperatures below 200 K and reaches its maximum of 60% at 18 T and 25 mK. The field- and temperature-dependent resistivity does not scale in a simple way. The opposite sign of the magnetoresistance at ambient and high pressure can be explained qualitatively by crystal-field effects lifting the degeneracy of the J = 7 2 groundstate. The linear coefficient of the specific heat (γ) measured at fields up to 10 T shows a quadratic field dependence. We did not find a linear relation between γ2 and A, the T2-coefficient of the temperature-dependent resistivity, with the applied magnetic field as the implicit parameter. © 1995.

Measurements of the temperature-dependent specific heat and thermal expansion coefficient near a T=0 magnetic-nonmagnetic boundary, accessed in CeRh2Si2 by application of pressure and in CeRh2-xRuxSi2 at ambient pressure by chemical substitution, emphasize the role of disorder in producing non-Fermi-liquid behavior. Interestingly, superconductivity also develops near this boundary in some crystallographically-ordered Ce-based heavy-fermion compounds. [CeRh2-xRuxSi2, specific heat, thermal expansion, susceptibility, non-Fermi-liquid]. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.

We present results for the resistivity, the magnetoresistance, and the specific heat of (Formula presented)(Formula presented)(Formula presented) and (Formula presented). The impurity contributions to these measurements follow the predictions of the single-impurity Kondo model for a Kondo temperature (Formula presented)≊65 K, assuming that the impurity behaves as a crystal-field split ((Formula presented)) doublet. Assuming a J=5/2 impurity, the value of (Formula presented) needed to fit these experiments varies from 65 to 125 K. The contribution to the susceptibility may be too small to be explained by the model. These results address whether the nonmagnetic impurity behaves as a Kondo hole. © 1996 The American Physical Society.

We report measurements of the resistivity ρ, Sommerfeld coefficient of specific heat γ, and magnetization M of polycrystalline YbAgCu4 in high magnetic fields 0≤B≤18 T [in the case of M(B) to 50 T]. A comparison of the temperature-dependent susceptibility χ(T) as well as field-dependent Sommerfeld coefficient γ and magnetization to Kondo theory for a J=7/2 impurity shows that theory correctly predicts the functional dependence of these quantities on T and B, but the characteristic temperatures determined from the various measurements (120, 98, 77, and 63 K) differ by nearly a factor of 2, which is difficult to understand within the context of Kondo theory even when other possible contributions are considered. In addition the normalized (Wilson) ratio of χ to γ is 1.00 at zero field (compared to 1.14 in Coqblin-Schrieffer theory) and decreases with increasing magnetic field. The magnetoresistance is positive at all temperatures, reaching a value Δρ(B)/ρ(B=0)=0.6 at 25 mK and 18 T. The low-temperature magnetoresistivity Δρ(B) varies as B1.5. We argue that this is dominated by an ordinary impurity effect. Kohler's rule is clearly violated as the temperature is raised; the scattering rate appears to increase with field below 40 K and decrease with field above 40 K. This behavior is expected for an Anderson lattice when a pseudogap is present. At low temperature the resistivity increases as AT2. The coefficient A (corrected for cyclotron-orbit effects) increases with field such that the ratio A(B)/γ(B)2 is a constant. Doping with Lu onto the Yb site, or with Ni onto the Cu site, changes the magnitude of the low-temperature resistivity in a manner consistent with the predictions of the theory of ligand-induced disorder in an Anderson lattice. © 1995 The American Physical Society.