394 research outputs found
Thermally activated exchange narrowing of the Gd3+ ESR fine structure in a single crystal of Ce1-xGdxFe4P12 (x = 0.001) skutterudite
We report electron spin resonance (ESR) measurements in the Gd3+ doped
semiconducting filled skutterudite compound Ce1-xGdxFe4P12 (x = 0.001). As the
temperature T varies from T = 150 K to T = 165 K, the Gd3+ ESR fine and
hyperfine structures coalesce into a broad inhomogeneous single resonance. At T
= 200 K the line narrows and as T increases further, the resonance becomes
homogeneous with a thermal broadening of 1.1(2) Oe/K. These results suggest
that the origin of these features may be associated to a subtle interdependence
of thermally activated mechanisms that combine: i) an increase with T of the
density of activated conduction-carriers across the T-dependent semiconducting
pseudogap; ii) the Gd3+ Korringa relaxation process due to an exchange
interaction, J_{fd}S.s, between the Gd3+ localized magnetic moments and the
thermally activated conduction-carriers and; iii) a relatively weak confining
potential of the rare-earth ions inside the oversized (Fe2P3)4 cage, which
allows the rare-earths to become rattler Einstein oscillators above T = 148 K.
We argue that the rattling of the Gd3+ ions, via a motional narrowing
mechanism, also contributes to the coalescence of the ESR fine and hyperfine
structure.Comment: 7 pages, 9 figures, accepted for publication in Phys Rev
Direct determination of the crystal field parameters of Dy, Er and Yb impurities in the skutterudite compound CeFeP by Electron Spin Resonance
Despite extensive research on the skutterudites for the last decade, their
electric crystalline field ground state is still a matter of controversy. We
show that Electron Spin Resonance (ESR) measurements can determine the full set
of crystal field parameters (CFPs) for the Th cubic symmetry (Im3) of the
CeRFeP (R = Dy, Er, Yb, )
skutterudite compounds. From the analysis of the ESR data the three CFPs, B4c,
B6c and B6t were determined for each of these rare-earths at the Ce
site. The field and temperature dependence of the measured magnetization for
the doped crystals are in excellent agreement with the one predicted by the
CFPs Bnm derived from ESR.Comment: 7 pages, 5 figures, to appear in PR
Esr In A Heavy-fermion Alloy (ube13) Doped With Local Moments
We have determined the ESR properties of UBe13 doped with dilute local moments of Er, Dy, or Gd over the temperature region where there is a large variation in the enhanced specific heat. We find that neither the enhancement, the temperature variation, nor any other anomalous behavior appears to be mirrored in the ESR data. We suggest that this unexpected result must be incorporated into current models of heavy-fermion systems. © 1985 The American Physical Society.55242719272
Unconventional Metallic Magnetism in LaCrSb{3}
Neutron-diffraction measurements in LaCrSb{3} show a coexistence of
ferromagnetic and antiferromagnetic sublattices below Tc=126 K, with ordered
moments of 1.65(4) and 0.49(4) Bohr magnetons per formula unit, respectively
(T=10 K), and a spin reorientation transition at ~95 K. No clear peak or step
was observed in the specific heat at Tc. Coexisting localized and itinerant
spins are suggested.Comment: PRL, in pres
Impurity Effect on Spin Ladder System
Effects of nonmagnetic impurity doping in a spin ladder system with a spin
gap are investigated by the exact diagonalization as well as by the variational
Monte Carlo calculations. Substantial changes in macroscopic properties such as
enhancements in spin correlations and magnetic susceptibilities are observed in
the low impurity concentration region, which are caused by the increase of
low-energy states. These results suggest that small but finite amount of
nonmagnetic impurity doping relevantly causes the reduction or the vanishment
of the spin gap. This qualitatively explains the experimental result of
Zn-doped SrCuO where small doping induces gapless nature. We
propose a possible scenario for this drastic change as a quantum phase
transition in a spin gapped ladder system due to spinon doping effects.Comment: 14 pages LaTeX including 5 PS figure
Quantum critical behavior induced by Mn impurity in CuGeO3
Results of high frequency (60-315 GHz) studies of ESR in CuGeO3 single
crystals containing 0.9% of Mn impurity are reported. Quantitative EPR line
shape analysis allowed concluding that low temperature magnetic susceptibility
for T <40 K diverges following power law with the critical exponent 0.81 and
therefore manifests onset of a quantum critical (QC) regime. We argue that
transition into Griffiths phase occurs at TG~40 K and disorder produced by Mn
impurity in quantum spin chains of CuGeO3 may lead to co-existence of the QC
regime and spin-Peierls dimerisation.Comment: 2 pages, submitted to SCES05 proceeding
High-field Electron Spin Resonance of Cu_{1-x}Zn_{x}GeO_{3}
High-Field Electron Spin Resonance measurements were made on powder samples
of Cu_{1-x}Zn_{x}GeO_{3} (x=0.00, 0.01, 0.02, 0.03 and 0.05) at different
frequencies (95, 110, 190, 220, 330 and 440 GHz) at low temperatures. The
spectra of the doped samples show resonances whose positions are dependent on
Zn concentration, frequency and temperature. The analysis of intensity
variation of these lines with temperature allows us to identify them as
originating in transitions within states situated inside the Spin Peierls gap.
A qualitative explanation of the details of the spectra is possible if we
assume that these states in the gap are associated with "loose" spins created
near the Zn impurities, as recently theoreticaly predicted. A new phenomenon of
quenching of the ESR signal across the Dimerized to Incommensurate
phase-boundary is observed.Comment: 4 pages, 5 ps figures in the text, submitted to Phys. Rev. Let
Eu2+ spin dynamics in the filled skutterudites EuM4Sb12 (M = Fe, Ru, Os)
We report evidence for a close relation between the thermal activation of the
rattling motion of the filler guest atoms, and inhomogeneous spin dynamics of
the Eu2+ spins. The spin dynamics is probed directly by means of Eu2+ electron
spin resonance (ESR), performed in both X-band (9.4 GHz) and Q-band (34 GHz)
frequencies in the temperature interval 4.2 < T < 300 K. A comparative study
with ESR measurements on the Beta-Eu8Ga16Ge30 clathrate compound is presented.
Our results point to a correlation between the rattling motion and the spin
dynamics which may be relevant for the general understanding of the dynamics of
cage systems.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev.
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