130 research outputs found
The magnetic response at the metal–insulator transition in La1−xSrxTiO3 (abstract)
We report on recent inelastic neutron scattering measurements of the magnetic response close to the metal–insulator transition in La1−xSrxTiO3. Specific heat and susceptibility data from Tokura et al. give evidence for a divergent effective mass at the critical concentration xc=0.05 in agreement with recent mean‐field theories of the transition. The mass enhancement is believed to arise from the formation of a d‐electron resonance at the Fermi energy close to the transition. The aim of this investigation is to look for evidence of this resonance in the dynamic magnetic susceptibility. We studied samples with x=0, 0.05, and 0.2 using incident energies between 25 and 200 meV. After correction for the phonon scattering, we observe a broad response above a threshold of 20–30 meV extending to over 100 meV. In addition, the Mott insulating antiferromagnet (x=0) has a peak at 40 meV, consistent with the estimated activation energy derived from resistivity measurements. This feature becomes washed out with temperature and doping. Possible origins for this peak are discussed. © 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70552/2/JAPIAU-79-8-6432-1.pd
The Transition from Heavy Fermion to Mixed Valence in Ce1-xYxAl3: A Quantitative Comparison with the Anderson Impurity Model
We present a neutron scattering investigation of Ce1-xYxAl3 as a function of
chemical pressure, which induces a transition from heavy-fermion behavior in
CeAl3 (TK=5 K) to a mixed-valence state at x=0.5 (TK=150 K). The crossover can
be modeled accurately on an absolute intensity scale by an increase in the k-f
hybridization, Vkf, within the Anderson impurity model. Surprisingly, the
principal effect of the increasing Vkf is not to broaden the low-energy
components of the dynamic magnetic susceptibility but to transfer spectral
weight to high energy.Comment: 4 pages, 5 figure
Electron doping evolution of the magnetic excitations in BaFe2-xNixAs2
We use inelastic neutron scattering (INS) spectroscopy to study the magnetic
excitations spectra throughout the Brioullion zone in electron-doped iron
pnictide superconductors BaFeNiAs with .
While the sample is near optimal superconductivity with K
and has coexisting static incommensurate magnetic order, the
samples are electron-overdoped with reduced of 14 K and 8 K,
respectively, and have no static antiferromagnetic (AF) order. In previous INS
work on undoped () and electron optimally doped () samples, the
effect of electron-doping was found to modify spin waves in the parent compound
BaFeAs below 100 meV and induce a neutron spin resonance at the
commensurate AF ordering wave vector that couples with superconductivity. While
the new data collected on the sample confirms the overall features of
the earlier work, our careful temperature dependent study of the resonance
reveals that the resonance suddenly changes its -width below similar
to that of the optimally hole-doped iron pnictides
BaKFeAs. In addition, we establish the dispersion of
the resonance and find it to change from commensurate to transversely
incommensurate with increasing energy. Upon further electron-doping to
overdoped iron pnictides with and 0.18, the resonance becomes weaker
and transversely incommensurate at all energies, while spin excitations above
100 meV are still not much affected. Our absolute spin excitation
intensity measurements throughout the Brillouin zone for
confirm the notion that the low-energy spin excitation coupling with itinerant
electron is important for superconductivity in these materials, even though the
high-energy spin excitations are weakly doping dependent.Comment: 16 pages, 16 figure
Crystal-fields in YbInNi4 determined with magnetic form factor and inelastic neutron scattering
The magnetic form factor of YbInNi4 has been determined via the flipping
ratios R with polarized neutron diffraction and the scattering function S(Q,w)
was measured in an inelastic neutron scattering experiment. Both experiments
were performed with the aim to determine the crystal-field scheme. The magnetic
form factor clearly excludes the possibility of a \Gamma7 doublet as the ground
state. The inelastic neutron data exhibit two, almost equally strong peaks at
3.2 meV and 4.4 meV which points, in agreement with earlier neutron data,
towards a \Gamma8 quartet ground state. Further possibilities like a
quasi-quartet ground state are discussed.Comment: 7 pages, 5 figures, 2 tables, submitted to PR
Evidence for a hybridization gap in noncentrosymmetric CeRuSi3
Inelastic neutron scattering (INS) and specific heat measurements have been performed on the intermediate valence compound CeRuSi3, which is isostructural to the noncentrosymmetric pressure-induced superconductors CeRhSi3, CeIrSi3, and CeCoGe3. INS measurements at 7 K reveal a broad peak at (58.5 ± 1.4) meV, while at 300 K, broad quasielastic scattering is observed. This indicates a large Kondo temperature of TK ~ 680 K. The magnetic contribution to the specific heat (Cmag) has a value of γ = 62.5(1) mJ/molK2 at low temperatures and above about 100 K can be well accounted for by the Coqblin-Schrieffer model with a characteristic temperature of T0 = 680 K, which is further evidence that CeRuSi3 is in the intermediate valence regime
Kondo behavior, ferromagnetic correlations, and crystal fields in the heavy Fermion compounds Ce3X (X=In, Sn)
We report measurements of inelastic neutron scattering, magnetic
susceptibility, magnetization, and the magnetic field dependence of the
specific heat for the heavy Fermion compounds CeIn and CeSn. The
neutron scattering results show that the excited crystal field levels have
energies = 13.2 meV, = 44.8 meV for CeIn and = 18.5 meV,
= 36.1 meV for CeSn. The Kondo temperature deduced from the
quasielastic linewidth is 17 K for CeIn and 40 K for CeSn. The low
temperature behavior of the specific heat, magnetization, and susceptibility
can not be well-described by J=1/2 Kondo physics alone, but require
calculations that include contributions from the Kondo effect, broadened
crystal fields, and ferromagnetic correlations, all of which are known to be
important in these compounds. We find that in CeIn the ferromagnetic
fluctuation makes a 10-15 % contribution to the ground state doublet entropy
and magnetization. The large specific heat coefficient in this heavy
fermion system thus arises more from the ferromagnetic correlations than from
the Kondo behavior.Comment: 8 pages, 6 figure
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