142 research outputs found
Exotic Kondo-hole band resistivity and magnetoresistance of CeLaOsSb alloys
Electrical resistivity measurements of non-magnetic single-crystalline
CeLaOsSb alloys, and 0.1, are reported for
temperatures down to 20 mK and magnetic fields up to 18 T. At the lowest
temperatures, the resistivity of CeLaOsSb has a
Fermi-liquid-like temperature variation , but with negative
in small fields. The resistivity has an unusually strong magnetic field
dependence for a paramagnetic metal. The 20 mK resistivity increases by 75%
between H=0 and 4 T and then decreases by 65% between 4 T and 18 T. Similarly,
the coefficient increases with the field from -77 to 29cmK between H=0 and 7 T and then decreases to 18cmK for 18 T. This nontrivial temperature and field variation
is attributed to the existence of a very narrow Kondo-hole band in the
hybridization gap, which pins the Fermi energy. Due to disorder the Kondo-hole
band has localized states close to the band edges. The resistivity for
has a qualitatively similar behavior to that of , but with a larger
Kondo-hole band
Magnetoresistance of PrLaOsSb: Disentangling local crystalline-electric-field physics and lattice effects
Resistivity measurements were performed on PrLaOsSb
single crystals at temperatures down to 20 mK and in fields up to 18 T. The
results for dilute-Pr samples ( and 0.67) are consistent with model
calculations performed assuming a singlet crystalline-electric-field (CEF)
ground state. The residual resistivity of these crystals features a smeared
step centered around 9 T, the predicted crossing field for the lowest CEF
levels. The CEF contribution to the magnetoresistance has a
weaker-than-calculated dependence on the field direction, suggesting that
interactions omitted from the CEF model lead to avoided crossing in the
effective levels of the Pr ion. The dome-shaped magnetoresistance
observed for and 0.05 cannot be reproduced by the CEF model, and likely
results from fluctuations in the field-induced antiferroquadrupolar phase
Anomalous low temperature state of CeOs4Sb12: Magnetic field and La-impurity study
Specific heat for single crystalline samples of Ce1-xLaxOs4Sb12 at zero-field
and magnetic fields to 14 T is reported. Our results confirm enhanced value of
the electronic specific heat coefficient in the paramagnetic state. They
provide arguments for the intrinsic origin of the 1.1 K anomaly. This
transition leads to opening of the gap at the Fermi surface. This low
temperature state of CeOs4Sb12 is extremely sensitive to chemical impurities.
2% of La substituted for Ce suppresses the transition and reduces the
electronic specific heat coefficient. The magnetic field response of the
specific heat is also anomalous.Comment: 4 pages, 3 figure
Glassy Spin Dynamics in Non-Fermi-Liquid UCu_{5-x}Pd_x, x = 1.0 and 1.5
Local f-electron spin dynamics in the non-Fermi-liquid heavy-fermion alloys
UCu_{5-x}Pd_x, x = 1.0 and 1.5, have been studied using muon spin-lattice
relaxation. The sample-averaged asymmetry function Gbar(t) indicates strongly
inhomogeneous spin fluctuations, and exhibits the scaling Gbar(t,H) =
Gbar(t/H^\gamma) expected from glassy dynamics. At 0.05 K \gamma(x=1.0) = 0.35
\pm 0.1, but \gamma(x=1.5) = 0.7 \pm 0.1. This is in contrast to inelastic
neutron scattering results, which yield \gamma = 0.33 for both concentrations.
There is no sign of static magnetism \gtrsim 10^{-3} \mu_B/U ion in either
material above 0.05 K. Our results strongy suggest that both alloys are quantum
spin glasses.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
Relationship between resistivity and specific heat in a canonical non-magnetic heavy fermion alloy system: UPt_5-xAu_x
UPt_(5-x)Au_x alloys form in a single crystal structure, cubic AuBe_5-type,
over a wide range of concentrations from x = 0 to at least x = 2.5. All
investigated alloys, with an exception for x = 2.5, were non-magnetic. Their
electronic specific heat coefficient varies from about 60 (x = 2) to
about 700 mJ/mol K^2 (x = 1). The electrical resistivity for all alloys has a
Fermi-liquid-like temperature variation, \rho = \rho_o + AT^2, in the limit of
T -> 0 K. The coefficient A is strongly enhanced in the heavy-fermion regime in
comparison with normal and transition metals. It changes from about 0.01 (x =
0) to over 2 micro-ohm cm/K^2 (x = 1). A/\gamma^2, which has been postulated to
have a universal value for heavy-fermions, varies from about 10^-6 (x = 0, 0.5)
to 10^-5 micro-ohm cm (mol K/mJ)^2 (x > 1.1), thus from a value typical of
transition metals to that found for some other heavy-fermion metals. This ratio
is unaffected, or only weakly affected, by chemical or crystallographic
disorder. It correlates with the paramagnetic Curie-Weiss temperature of the
high temperature magnetic susceptibility.Comment: 5 pages, 5 eps figures, RevTe
Order and nFl Behavior in UCu4Pd
We have studied the role of disorder in the non-Fermi liquid system UCu4Pd
using annealing as a control parameter. Measurement of the lattice parameter
indicates that this procedure increases the crystallographic order by
rearranging the Pd atoms from the 16e to the 4c sites. We find that the low
temperature properties depend strongly on annealing. Whereas the non-Fermi
liquid behavior in the specific heat can be observed over a larger temperature
range after annealing, the clear non-Fermi liquid behavior of the resistivity
of the unannealed sample below 10 K disappears. We come to the conclusion that
this argues against the Kondo disorder model as an explanation for the
non-Fermi liquid properties of both as-prepared and annealed UCu4Pd
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