129 research outputs found
Microscopic analysis of multipole susceptibility of actinide dioxides: A scenario of multipole ordering in AmO
By evaluating multipole susceptibility of a seven-orbital impurity Anderson
model with the use of a numerical renormalization group method, we discuss
possible multipole states of actinide dioxides at low temperatures. In
particular, here we point out a possible scenario for multipole ordering in
americium dioxide. For Am ion with five electrons, it is considered
that the ground state is doublet and the first excited state is
quartet, but we remark that the ground state is easily
converted due to the competition between spin-orbit coupling and Coulomb
interactions. Then, we find that the quartet can be the ground
state of AmO even for the same crystalline electric field potential. In the
case of quartet ground state, the numerical results suggest that
high-order multipoles such as quadrupole and octupole can be relevant to
AmO.Comment: 8 pages, 4 figures. To appear in Phys. Rev.
The magnetic structure of the chain family NaCaVO determined by muon-spin rotation
We present muon-spin rotation measurements on polycrystalline samples of the
complete family of the antiferromagnetic (AF) chain compounds,
NaCaVO. In this family, we explore the magnetic properties
from the metallic NaVO to the insulating CaVO. We find a
critical which separates the low and high Na-concentration
dependent transition temperature and its magnetic ground state. In the
compounds, the magnetic ordered phase is characterized by a single homogenous
phase and the formation of incommensurate spin-density-wave order. Whereas in
the compounds, multiple sub-phases appear with temperature and .
Based on the muon data obtained in zero external magnetic field, a careful
dipolar field simulation was able to reproduce the muon behavior and indicates
a modulated helical incommensurate spin structure of the metallic AF phase. The
incommensurate modulation period obtained by the simulation agrees with that
determined by neutron diffraction.Comment: 7 pages, 7 figures, accepted for publication in PR
Magnetism of PdNi alloys near the critical concentration for ferromagnetism
We report results of a muon spin rotation and relaxation (SR) study of
dilute PdNi alloys, with emphasis on Ni concentrations 0.0243
and 0.025. These are close to the critical value for the onset
of ferromagnetic long-range order (LRO), which is a candidate for a quantum
critical point. The 2.43 and 2.5 at.% Ni alloys exhibit similar SR
properties. Both samples are fully magnetic, with average muon local fields
2.0 and 3.8 mT and Curie temperatures
1.0 and 2.03 K for 2.43 and 2.5 at.% Ni, respectively, at . The
temperature dependence of suggests ordering of
Ni spin clusters rather than isolated spins. Just above a two-phase
region is found with separate volume fractions of quasistatic short-range order
(SRO) and paramagnetism. The SRO fraction decreases to zero with increasing
temperature a few kelvin above . This mixture of SRO and paramagnetism is
consistent with the notion of an inhomogeneous alloy with Ni clustering. The
measured values of extrapolate to = 0.0236 0.0027.
The dynamic muon spin relaxation in the vicinity of differs for the two
samples: a relaxation-rate maximum at is observed for = 0.0243,
reminiscent of critical slowing down, whereas for 0.025 no dynamic
relaxation is observed within the SR time window. The data suggest a
mean-field-like transition in this alloy.Comment: 15 pages, 15 figures, to be published in Phys. Rev.
Probing the magnetic ground state of the molecular Dysprosium triangle
We present zero field muon spin lattice relaxation measurements of a
Dysprosium triangle molecular magnet. The local magnetic fields sensed by the
implanted muons indicate the coexistence of static and dynamic internal
magnetic fields below K. Bulk magnetization and heat capacity
measurements show no indication of magnetic ordering below this temperature. We
attribute the static fields to the slow relaxation of the magnetization in the
ground state of Dy3. The fluctuation time of the dynamic part of the field is
estimated to be ~0.55 s at low temperaturesComment: 5 pages, 5 figures, accepted for publication in Phys. Rev.
Two dimensionality in quasi one-dimensional cobalt oxides
By means of muon spin rotation and relaxation (SR) techniques, we have
investigated the magnetism of quasi one-dimensional (1D) cobalt oxides
CoO (=Ca, Sr and Ba, =1, 2, 3, 5 and
), in which the 1D CoO chain is surrounded by six equally spaced
chains forming a triangular lattice in the -plane, using polycrystalline
samples, from room temperature down to 1.8 K. For the compounds with =1 - 5,
transverse field SR experiments showed the existence of a magnetic
transition below 100 K. The onset temperature of the transition () was found to decrease with ; from 100 K for =1 to 60 K for
=5. A damped muon spin oscillation was observed only in the sample with
=1 (CaCoO), whereas only a fast relaxation obtained even at 1.8
K in the other three samples. In combination with the results of susceptibility
measurements, this indicates that a two-dimensional short-range
antiferromagnetic (AF) order appears below for all
compounds with =1 - 5; but quasi-static long-range AF order formed only in
CaCoO, below 25 K. For BaCoO (=), as decreased
from 300 K, 1D ferromagnetic (F) order appeared below 53 K, and a sharp 2D AF
transition occurred at 15 K.Comment: 12 pages, 14 figures, and 2 table
The magnetic phase of the perovskite CaCrO studied with SR
We investigated the magnetic phase of the perovskite CaCrO by using the
muon spin relaxation technique accompanied by susceptibility measurements. A
thermal hysteresis loop is identified with a width of about 1 K at the
transition temperature. Within the time scale of the muon lifetime, a static
antiferromagnetic order is revealed with distinct multiple internal fields
which are experienced in the muon interstitial sites below the phase-transition
temperature, . Above , lattice deformations are indicated by
transverse-field muon-spin rotation and relaxation suggesting a magneto-elastic
mechanism.Comment: 5 pages, 4 figures. Accepted for publication in PR
The Herbertsmithite Hamiltonian: SR measurements on single crystals
We present transverse field muon spin rotation/relaxation measurements on
single crystals of the spin-1/2 kagome antiferromagnet Herbertsmithite. We find
that the spins are more easily polarized when the field is perpendicular to the
kagome plane. We demonstrate that the difference in magnetization between the
different directions cannot be accounted for by Dzyaloshinksii-Moriya type
interactions alone, and that anisotropic axial interaction is present.Comment: 8 pages, 3 figures, accepted to JPCM special issue on geometrically
frustrated magnetis
Transport properties of moderately disordered UCuPd
We present a detailed study on the (magneto)transport properties of as-cast
and heat treated material UCuPd. We find a pronounced sample dependence of
the resistivity of as-cast samples, and reproduce the annealing
dependence of . In our study of the Hall effect we determine a metallic
carrier density for all samples, and a temperature dependence of the Hall
constant which is inconsistent with the Skew scattering prediction. The
magnetoresistive response is very small and characteristic for spin disorder
scattering, suggesting that overall the resistivity is controlled mostly by
nonmagnetic scattering processes. We discuss possible sources for the
temperature and field dependence of the transport properties, in particular
with respect to quantum criticality and electronic localization effects.Comment: 11 pages, 9 figures, submitted PR
Li diffusion in LiCoO probed by muon-spin spectroscopy
The diffusion coefficient of Li ions () in the battery
material LiCoO has been investigated by muon-spin relaxation
(SR). Based on the experiments in zero-field and weak
longitudinal-fields at temperatures up to 400 K, we determined the fluctuation
rate () of the fields on the muons due to their interaction with the
nuclear moments. Combined with susceptibility data and electrostatic potential
calculations, clear Li ion diffusion was detected above K. The
estimated from was in very good agreement with predictions
from first-principles calculations, and we present the SR technique as
an % novel and optimal probe to detect for materials containing
magnetic ions.Comment: 4 pages, 4 figures. accepted for publication in PR
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