384 research outputs found
Disorder, inhomogeneity and spin dynamics in f-electron non-Fermi liquid systems
Muon spin rotation and relaxation (SR) experiments have yielded evidence
that structural disorder is an important factor in many f-electron-based
non-Fermi-liquid (NFL) systems. Disorder-driven mechanisms for NFL behaviour
are suggested by the observed broad and strongly temperature-dependent SR
(and NMR) linewidths in several NFL compounds and alloys. Local disorder-driven
theories (Kondo disorder, Griffiths-McCoy singularity) are, however, not
capable of describing the time-field scaling seen in muon spin relaxation
experiments, which suggest cooperative and critical spin fluctuations rather
than a distribution of local fluctuation rates. A strong empirical correlation
is established between electronic disorder and slow spin fluctuations in NFL
materialsComment: 24 pages, 15 figures, submitted to J. Phys.: Condens. Matte
Knight Shift Anomalies in Heavy Electron Materials
We calculate non-linear Knight Shift vs. susceptibility anomalies
for Ce ions possessing local moments in metals. The ions are modeled with the
Anderson Hamiltonian and studied within the non-crossing approximation (NCA).
The non-linearity diminishes with decreasing Kondo temperature
and nuclear spin- local moment separation. Treating the Ce ions as an
incoherent array in CeSn, we find excellent agreement with the observed Sn
data.Comment: 4 pages, Revtex, 3 figures available upon request from
[email protected]
Z_2-vortex ordering of the triangular-lattice Heisenberg antiferromagnet
Ordering of the classical Heisenberg antiferromagnet on the triangular
lattice is studied by means of a mean-field calculation, a scaling argument and
a Monte Carlo simulation, with special attention to its vortex degree of
freedom. The model exhibits a thermodynamic transition driven by the Z_2-vortex
binding-unbinding, at which various thermodynamic quantities exhibit an
essential singularity. The low-temperature state is a "spin-gel" state with a
long but finite spin correlation length where the ergodicity is broken
topologically. Implications to recent experiments on triangular-lattice
Heisenberg antiferromagnets are discussed
Pd/Cu Site Interchange and Non-Fermi-Liquid Behavior in UCu_4Pd
X-ray-absorption fine-structure measurements of the local structure in
UCu_4Pd are described which indicate a probable lattice-disorder origin for
non-Fermi-liquid behavior in this material. Short Pd-Cu distances are observed,
consistent with 24 +/- 3% of the Pd atoms occupying nominally Cu sites. A
"Kondo disorder" model, based on the effect on the local Kondo temperature T_K
of this interchange and some additional bond-length disorder, agrees
quantitatively with previous experimental susceptibility data, and therefore
also with specific heat and magnetic resonance experiments.Comment: 4 pages, 3 PostScript figures, to be published in PR
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Mesoscopic phase separation in La2CuO4.02 - a 139La NQR study
In crystals of La2CuO4.02 oxygen diffusion can be limited to such small
length scales, that the resulting phase separation is invisible for neutrons.
Decomposition of the 139La NQR spectra shows the existence of three different
regions, of which one orders antiferromagnetically below 17K concomitantly with
the onset of a weak superconductivity in the crystal. These regions are
compared to the macroscopic phases seen previously in the title compound and
the cluster-glass and striped phases reported for the underdoped Sr-doped
cuprates.Comment: 4 pages, RevTeX, 5 figures, to be published in PR
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Theory of Impurity Effects on the Spin Nematic State
The effect of magnetic bond disorder in otherwise antiferro nematic ordered
system is investigated. We introduced triangular-shaped ferromagnetic bond
disorder in the S=1 bilinear-biquadratic model on a triangular lattice. It is
shown that the coupling between the impurity magnetic moment and nonmagnetic
excitation in the bulk yields single-moment anisotropy and long-range
anisotropic interaction between impurity magnetic moments. This interaction can
induce unconventional spin-freezing phenomena observed in triangular magnet,
NiGa2S4.Comment: 19 pages, 14 figure
What Does The Korringa Ratio Measure?
We present an analysis of the Korringa ratio in a dirty metal, emphasizing
the case where a Stoner enhancement of the uniform susceptibilty is present. We
find that the relaxation rates are significantly enhanced by disorder, and that
the inverse problem of determining the bare density of states from a study of
the change of the Knight shift and relaxation rates with some parameter, such
as pressure, has rather constrained solutions, with the disorder playing an
important role. Some preliminary applications to the case of chemical
substitution in the RbKC family of superconductors is
presented and some other relevant systems are mentioned.Comment: 849, Piscataway, New Jersey 08855 24 June 199
Spin dynamics and ordering of a cuprate stripe-antiferromagnet
In La1.48Nd0.4Sr0.12CuO4 the 139La and 63Cu NQR relaxation rates and signal
wipe-out upon lowering temperature are shown to be due to purely magnetic
fluctuations. They follow the same renormalized classical behavior as seen in
neutron data, when the electronic spins order in stripes, with a small spread
in spin stiffness (15% spread in activation energy). The La signal, which
reappears at low temperatures, is magnetically broadened and experiences
additional wipe-out due to slowing down of the Nd fluctuations.Comment: 4 pages including 3 figures - ref. 16 adde
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