106 research outputs found
Magnetic and electric properties in the distorted tetrahedral spin chain system Cu3Mo2O9
We study the multiferroic properties in the distorted tetrahedral quasi-one
dimensional spin system CuMoO, in which the effects of the low
dimensionality and the magnetic frustration are expected to appear
simultaneously. We clarify that the antiferromagnetic order is formed together
with ferroelectric properties at K under zero magnetic field
and obtain the magnetic-field-temperature phase diagram by measuring dielectric
constant and spontaneous electric polarization. It is found that the
antiferromagnetic phase possesses a spontaneous electric polarization parallel
to the c axis when the magnetic field is applied parallel to the a axis. On
the other hand, there are three different ferroelectric phases in the
antiferromagnetic phase for parallel to the c axis.Comment: 4 pages, 3 figures, LT26 proceedings, accepted for publication in J.
Phys.: Conf. Se
Longitudinal magnetic excitation in KCuCl3 studied by Raman scattering under hydrostatic pressures
We measure Raman scattering in an interacting spin-dimer system KCuCl3 under
hydrostatic pressures up to 5 GPa mediated by He gas. In the pressure-induced
quantum phase, we observe a one-magnon Raman peak, which originates from the
longitudinal magnetic excitationand is observable through the second-order
exchange interaction Raman process. We report the pressure dependence of the
frequency, halfwidth and Raman intensity of this mode.Comment: 4 pages, 3 figures, inpress in JPCS as a proceeding of LT2
Spin fluctuations in CuGeO probed by light scattering
We have measured temperature dependence of low-frequency Raman spectra in
CuGeO, and have observed the quasi-elastic scattering in the
polarization above the spin-Peierls transition temperature. We attribute it to
the fluctuations of energy density in the spin system. The magnetic specific
heat and an inverse of the magnetic correlation length can be derived from the
quasi-elastic scattering. The inverse of the magnetic correlation length is
proportional to at high temperatures. We compare the
specific heat with a competing- model. This model cannot explain
quantitatively both the specific heat and the magnetic susceptibility with the
same parameters. The origin of this discrepancy is discussed.Comment: 17 pages, REVTeX, 5 Postscript figures; in press in PR
Magnetic and Dielectric Properties in Multiferroic Cu3Mo2O9 under High Magnetic Fields
The magnetic and dielectric properties under high magnetic fields are studied
in the single crystal of Cu3Mo2O9. This multiferroic compound has distorted
tetrahedral spin chains. The effects of the quasi-one dimensionality and the
geometrical spin frustration are expected to appear simultaneously. We measure
the magnetoelectric current and the differential magnetization under the pulsed
magnetic field up to 74 T. We also measure the electric polarization versus the
electric field curve/loop under the static field up to 23 T. Dielectric
properties change at the magnetic fields where the magnetization jumps are
observed in the magnetization curve. Moreover, the magnetization plateaus are
found at high magnetic fields.Comment: 6 pages, 3 figures, in press in JPS Conf. Proc. as a part of SCES2013
Proceeding
Spin-phonon coupled modes in the incommensurate phases of doped CuGeO
The doping effect of the folded phonon mode at 98 cm was investigated
on the Si-doped CuGeO by magneto-optical measurements in far-infrared (FIR)
region under high magnetic field. The folded phonon mode at 98 cm
appears not only in the dimerized (D) phase but also in the
dimerized-anitiferromagnetic (DAF) phase on the doped CuGeO. The splitting
was observed in the incommensurate (IC) phase and the antiferromagnetically
ordered incommensurate (IAF) phase above . The split-off branches exhibit
different field dependence from that of the pure CuGeO in the vicinity of
, and the discrepancy in the IAF phase is larger than that in the IC
phase. It is caused by the interaction between the solitons and the impurities.Comment: 7 pages, 4 figures, resubmitted to Phys. Rev.
Confirmation of a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor and antiferromagnetic second-nearest-neighbor interactions in RbCuMoO
We have investigated magnetic properties of RbCuMoO
powder. Temperature dependence of magnetic susceptibility and magnetic-field
dependence of magnetization have shown that this cuprate is a model compound of
a one-dimensional spin-1/2 Heisenberg system with ferromagnetic
first-nearest-neighbor (1NN) and antiferromagnetic second-nearest-neighbor
(2NN) competing interactions (competing system). Values of the 1NN and 2NN
interactions are estimated as K and K (). This value of suggests that the ground state is a
spin-singlet incommensurate state. In spite of relatively large and
, no magnetic phase transition appears down to 2 K, while an
antiferromagnetic transition occurs in other model compounds of the competing
system with ferromagnetic 1NN interaction. For that reason,
RbCuMoO is an ideal model compound to study properties of
the incommensurate ground state that are unconfirmed experimentally.Comment: 6 pages, 4 figure
Spin gap behavior and charge ordering in \alpha^{\prime}-NaV_2O_5 probed by light scattering
We present a detailed analysis of light scattering experiments performed on
the quarter-filled spin ladder compound -NaVO for
the temperature range 5 KT300 K. This system undergoes a phase
transition into a singlet ground state at T=34 K accompanied by the formation
of a super structure. For T34 K several new modes were detected. Three of
these modes are identified as magnetic bound states. Experimental evidence for
charge ordering on the V sites is detected as an anomalous shift and splitting
of a V-O vibration at 422 cm for temperatures above 34 K. The smooth and
crossover-like onset of this ordering at T= 80 K is accompanied by
pretransitional fluctuations both in magnetic and phononic Raman scattering. It
resembles the effect of stripe order on the super structure intensities in
LaNiO.Comment: 36 pages, 11 figures, accepted for publication in PRB (sept.99
Electric polarization induced by Neel order without magnetic superlattice: experimental study of Cu3Mo2O9 and numerical study of a small spin cluster
We clarify that the antiferromagnetic order in the distorted tetrahedral
quasi-one dimensional spin system induces electric polarizations. In this
system, the effects of the low dimensionality and the magnetic frustration are
expected to appear simultaneously. We obtain the magnetic-field-temperature
phase diagram in Cu3Mo2O9 by studying the dielectric constant and the
spontaneous electric polarization. Around the tricritical point at 10 T and 8
K, the change of the direction in the electric polarization causes a colossal
magnetocapacitance. We calculate the charge redistribution in the small spin
cluster consisting of two magnetic tetrahedra to demonstrate the electric
polarization induced by the antiferromagnetism.Comment: 10 pages 6 figures, in press in J. Phys. Soc. Jp
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