467 research outputs found
muSR study of the Cu-spin dynamics in the electron-doped high-Tc cuprate of Pr0.86LaCe0.14Cu1-y(Zn,Ni)yO4
Effects of the Zn- and Ni-substitution on the Cu-spin dynamics in the
electron-doped Pr0.86LaCe0.14Cu1-y(Zn,Ni)yO4+a-d with y = 0, 0.01, 0.02, 0.05
and different values of the reduced oxygen content d have been studied using
zero-field muon-spin-relaxation (muSR) measurements at temperatures down to 2
K. For the as-grown sample (d = 0, y = 0) and the sample with a very small d
value (d < 0.01, y = 0), a muon-spin precession due to long-range
antiferromagnetic order has been observed. On the other hand, no precession has
been observed for moderately oxygen-reduced samples (0.01 < d < 0.09). It has
been found that for all the samples of 0.01 < d < 0.09 the asymmetry A(t) (muSR
time spectrum) in the long-time region increases with decreasing temperature at
low temperatures, suggesting possible slowing-down of the Cu-spin fluctuations.
On the other hand, no significant difference between Zn- and Ni-substitution
effects on the slowing down of the Cu-spin fluctuations has been observed.Comment: 4 pages, 2 figures, Proceeding of 10th muSR conference 2005, to be
published in Physica
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
Absence of the impurity-induced magnetic order in the electron-doped high-T_c_ cuprates Pr_0.86_LaCe_0.14_Cu_1-y_(Zn, Ni)_y_O_4_
Zero-field muon-spin-relaxation measurements have been carried out in order
to investigate the Zn- and Ni-substitution effects on the Cu-spin dynamics in
the electron-doped Pr_0.86_LaCe_0.14_Cu_1-y_(Zn, Ni)_y_O_4+\alpa-\delta_ with y
= 0, 0.01, 0.02, 0.05 and different values of the reduced oxygen content
\delta(\delta \le 0.09). For the samples with y = 0 and very small \delta
values of \delta < 0.01, a muon-spin precession due to the formation of a
long-range antiferromagnetic order has been observed at low temperatures below
\~ 5 K. For the moderately oxygen-reduced samples of 0.01 \le \delta \le 0.09,
on the contrary, no muon-spin precession has been observed and the temperature
dependence of the spectra is similar to one another regardless of the y value.
That is, no impurity-induced slowing down of the Cu-spin fluctuations has been
detected, which is very different from the results of the hole-doped high-T_c_
cuprates. The reason is discussed.Comment: 13 pages, 2 figures, Proceedings of ISS2004 (to be published in
Physica C
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