457 research outputs found
Magnetic ground state of pyrochlore oxides close to metal-insulator boundary probed by muon spin rotation
Magnetism of ruthernium pyrochlore oxides A2Ru2O7 (A = Hg, Cd, Ca), whose
electronic properties within a localized ion picture are characterized by
non-degenerate t2g orbitals (Ru5+, 4d3) and thereby subject to geometrical
frustration, has been investigated by muon spin rotation/relaxation (muSR)
technique. The A cation (mostly divalent) was varied to examine the effect of
covalency (Hg > Cd > Ca) on their electronic property. In a sample with A = Hg
that exhibits a clear metal-insulator (MI) transition below >> 100 K (which is
associated with a weak structural transition), a nearly commensurate magnetic
order is observed to develop in accordance with the MI transition. Meanwhile,
in the case of A = Cd where the MI transition is suppressed to the level of
small anomaly in the resistivity, the local field distribution probed by muon
indicates emergence of a certain magnetic inhomogeneity below {\guillemotright}
30 K. Moreover, in Ca2Ru2O7 that remains metallic, we find a highly
inhomogeneous local magnetism below >>25 K that comes from randomly oriented Ru
moments and thus described as a "frozen spin liquid" state. The systematic
trend of increasing randomness and itinerant character with decreasing
covalency suggests close relationship between these two characters. As a
reference for the effect of orbital degeneracy and associated Jahn-Teller
instability, we examine a tetravalent ruthernium pyrochlore, Tl2Ru2O7 (Ru4+,
4d4), where the result of muSR indicates a non-magnetic ground state that is
consistent with the formation of the Haldane chains suggested by neutron
diffraction experiment.Comment: 12 pages, 13 figure
EFFECTS OF FATIGUE ON THE GROUND REACTION FORCES AND LEG KINEMATICS IN ALL-OUT 600 METERS RUNNING
The purpose of this study was to investigate effects of fatigue on the ground reaction forces and leg kinematics during all-out 600m running, which was performed by eight male middle-distance runners. Their running motion was videotaped (300Hz) and the ground reaction forces were measured (500Hz) at the 150m and 550m marks of the 600m running. From the 150m to 550m mark, running speed significantly decreased (
Local electronic structure of interstitial hydrogen in MgH inferred from muon study
Magnesium hydride has great potential as a solid hydrogen (H) storage
material because of its high H storage capacity of 7.6 wt%. However, its slow
hydrogenation and dehydrogenation kinetics and the high temperature of 300
C required for decomposition are major obstacles to small-scale
applications such as automobiles. The local electronic structure of
interstitial H in MgH is an important fundamental knowledge in solving this
problem, which has been studied mainly based on density functional theory
(DFT). However, few experimental studies have been performed to assess the
results of DFT calculations. We have therefore introduced muon (Mu) as pseudo-H
into MgH and investigated the corresponding interstitial H states by
analyzing their electronic and dynamical properties in detail. As a result, we
observed multiple Mu states similar to those observed in wide-gap oxides, and
found that their electronic states can be attributed to relaxed-excited states
associated with donor/acceptor levels predicted by the recently proposed
"ambipolarity model". This provides an indirect support for the DFT
calculations on which the model is based via the donor/acceptor levels. An
important implication of the muon results for improved hydrogen kinetics is
that dehydrogenation, serving as a for hydrides, stabilizes the
interstitial H state.Comment: 14 pages, 9 figure
High-pressure study on the superconducting pyrochlore oxide Cd2Re2O7
Superconducting and structural phase transitions in a pyrochlore oxide
Cd2Re2O7 are studied under high pressure by x-ray diffraction and electrical
resistivity measurements. A rich P-T phase diagram is obtained, which contains
at least two phases with the ideal and slightly distorted pyrochlore
structures. It is found that the transition between them is suppressed with
increasing pressure and finally disappears at a critical pressure Pc = 3.5 GPa.
Remarkable enhancements in the residual resistivity as well as the coefficient
A of the AT 2 term in the resistivity are found around the critical pressure.
Superconductivity is detected only for the phase with the structural
distortion. It is suggested that the charge fluctuations of Re ions play a
crucial role in determining the electronic properties of Cd2Re2O7.Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jp
Direct observation of oxygen polarization in SrIrO by O -edge x-ray magnetic circular dichroism
X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD)
measurements at the oxygen (O) -edge were performed to investigate the
magnetic polarization of ligand O atoms in the weak ferromagnetic (WFM) phase
of the Ir perovskite compound SrIrO. With the onset of the WFM phase
below K, XMCD signals corresponding to XAS peaks
respectively identified as originating from the magnetic moments of apical and
planar oxygen (O and O) in the IrO octahedra were
observed. The observation of magnetic moments at O sites is
consistent (except for the relative orientation) with that suggested by prior
muon spin rotation (SR) experiment in the non-collinear antiferromagnetic
(NC-AFM) phase below K. Assuming that the O
magnetic moment observed by SR is also responsible for the corresponding
XMCD signal, the magnetic moment of O is estimated to be consistent
with the previous SR result. Since the O XMCD signal is mainly
contributed by Ir 5 and orbitals which also hybridize with O, it is inferred that the relatively large O magnetic moment is
induced by Ir 5 orbitals. Moreover, the inversion of O
moments relative to Ir moments between the two magnetic phases revealed by XMCD
suggests the presence of competing magnetic interactions for O, with
which the ordering of O moments in the NC-AFM phase may be suppressed
to .Comment: 6 pages, 6 figure
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