464 research outputs found
Magnetic Transition in the Kondo Lattice System CeRhSn2
Our resistivity, magnetoresistance, magnetization and specific heat data
provide unambiguous evidence that CeRhSn2 is a Kondo lattice system which
undergoes magnetic transition below 4 K.Comment: 3 pages text and 5 figure
Muon Spin Relaxation Studies of Superconductivity in a Crystalline Array of Weakly Coupled Metal Nanoparticles
We report Muon Spin Relaxation studies in weak transverse fields of the
superconductivity in the metal cluster compound,
Ga[N(SiMe)]-LiBr(thf)2toluene. The temperature and field dependence of the muon spin relaxation
rate and Knight shift clearly evidence type II bulk superconductivity below
K, with T,
T, and weak flux pinning. The data
are well described by the s-wave BCS model with weak electron-phonon coupling
in the clean limit. A qualitative explanation for the conduction mechanism in
this novel type of narrow band superconductor is presented.Comment: 4 figures, 5 page
Proximity effects in the superconductor / heavy fermion bilayer system Nb / CeCu_6
We have investigated the proximity effect between a superconductor (Nb) and a
'Heavy Fermion' system (CeCu_6) by measuring critical temperatures and
parallel critical fields H_{c2}^{\parallel}(T) of Nb films with varying
thickness deposited on 75 nm thick films of CeCu_6, and comparing the results
with the behavior of similar films deposited on the normal metal Cu. For Nb on
CeCu_6 we find a strong decrease of T_c with decreasing Nb thickness and a
finite critical thickness of the order of 10 nm. Also, dimensional crossovers
in H_{c2}^{\parallel}(T) are completely absent, in strong contrast with Nb/Cu.
Analysis of the data by a proximity effect model based on the Takahashi-Tachiki
theory shows that the data can be explained by taking into account both the
high effective mass (or low electronic diffusion constant), {\it and} the large
density of states at the Fermi energy which characterize the Heavy Fermion
metal.Comment: 7 pages, 2 figure. Manuscript has been submitted to a refereed
journa
Magnetism of PdNi alloys near the critical concentration for ferromagnetism
We report results of a muon spin rotation and relaxation (SR) study of
dilute PdNi alloys, with emphasis on Ni concentrations 0.0243
and 0.025. These are close to the critical value for the onset
of ferromagnetic long-range order (LRO), which is a candidate for a quantum
critical point. The 2.43 and 2.5 at.% Ni alloys exhibit similar SR
properties. Both samples are fully magnetic, with average muon local fields
2.0 and 3.8 mT and Curie temperatures
1.0 and 2.03 K for 2.43 and 2.5 at.% Ni, respectively, at . The
temperature dependence of suggests ordering of
Ni spin clusters rather than isolated spins. Just above a two-phase
region is found with separate volume fractions of quasistatic short-range order
(SRO) and paramagnetism. The SRO fraction decreases to zero with increasing
temperature a few kelvin above . This mixture of SRO and paramagnetism is
consistent with the notion of an inhomogeneous alloy with Ni clustering. The
measured values of extrapolate to = 0.0236 0.0027.
The dynamic muon spin relaxation in the vicinity of differs for the two
samples: a relaxation-rate maximum at is observed for = 0.0243,
reminiscent of critical slowing down, whereas for 0.025 no dynamic
relaxation is observed within the SR time window. The data suggest a
mean-field-like transition in this alloy.Comment: 15 pages, 15 figures, to be published in Phys. Rev.
Evolution of Quantum Criticality in CeNi_{9-x}Cu_xGe_4
Crystal structure, specific heat, thermal expansion, magnetic susceptibility
and electrical resistivity studies of the heavy fermion system
CeNi_{9-x}Cu_xGe_4 (0 <= x <= 1) reveal a continuous tuning of the ground state
by Ni/Cu substitution from an effectively fourfold degenerate non-magnetic
Kondo ground state of CeNi_9Ge_4 (with pronounced non-Fermi-liquid features)
towards a magnetically ordered, effectively twofold degenerate ground state in
CeNi_8CuGe_4 with T_N = 175 +- 5 mK. Quantum critical behavior, C/T ~ \chi ~
-ln(T), is observed for x about 0.4. Hitherto, CeNi_{9-x}Cu_xGe_4 represents
the first system where a substitution-driven quantum phase transition is
connected not only with changes of the relative strength of Kondo effect and
RKKY interaction, but also with a reduction of the effective crystal field
ground state degeneracy.Comment: 15 pages, 9 figure
- …