742 research outputs found
Existence of a phase transition under finite magnetic field in the long-range RKKY Ising spin glass DyYRuSi
A phase transition of a model compound of the long-range Ising spin glass
(SG) DyYRuSi, where spins interact via the RKKY
interaction, has been investigated. The static and the dynamic scaling analyses
reveal that the SG phase transition in the model magnet belongs to the
mean-field universality class. Moreover, the characteristic relaxation time in
finite magnetic fields exhibits a critical divergent behavior as well as in
zero field, indicating a stability of the SG phase in finite fields. The
presence of the SG phase transition in field in the model magnet strongly
syggests that the replica symmetry is broken in the long-range Ising SG.Comment: 4 pages, 4 figures, to be published in JPSJ (2010
Orbital-Order Driven Ferroelectricity and Dipolar Relaxation Dynamics in Multiferroic GaMoS
We present the results of broadband dielectric spectroscopy of GaMoS,
a lacunar spinel system that recently was shown to exhibit non-canonical,
orbitally-driven ferroelectricity. Our study reveals complex relaxation
dynamics of this multiferroic material, both above and below its Jahn-Teller
transition at T K. Above T, two types of
coupled dipolar-orbital dynamics seem to compete: relaxations within
cluster-like regions with short-range polar order like in relaxor
ferroelectrics and critical fluctuations of only weakly interacting dipoles,
the latter resembling the typical dynamics of order-disorder type
ferroelectrics. Below the Jahn-Teller transition, the onset of orbital order
drives the system into long-range ferroelectric order and dipolar dynamics
within the ferroelectric domains is observed. The coupled dipolar and orbital
relaxation behavior of GaMoS above the Jahn-Teller transition markedly
differs from that of the skyrmion host GaVS, which seems to be linked
to differences in the structural distortions of the two systems on the
unit-cell level.Comment: 6 pages, 3 figures + Supplemental Material (2 pages, 2 figures
Itinerant electron magnetism of η-carbides Co6M6C and Ni6M6C (M=Mo and W)
Magnetic, transport, and thermal properties of metallic η-carbides Co6M6C and Ni6M6C (M = Mo and W) with the cubic Ni6Mo6C-type structure have been characterized. The Ni-based compounds Ni6Mo6C and Ni6W6C are Pauli paramagnets with temperature-independent susceptibilities. Susceptibilities of the Co-based compounds Co6Mo6C and Co6W6C are enhanced and temperature-dependent. Co6Mo6C remains paramagnetic down to the lowest temperature, while Co6W6C undergoes an antiferromagnetic-type transition at 46 K. A metamagnetic transition was observed for Co6W6C at 20–30 T at the lowest temperatures. The correlation among the enhancements in the susceptibility, the resistivity, and the electronic specific heat suggests the presence of moderate electron correlation in these compounds
Possible Spin-triplet Superconductivity in NaxCoO2yH2O - 59Co NMR Study
We report 59Co NMR studies on the magnetically oriented powder samples of
Co-oxide superconductors NaxCoO2yH2O with Tc ~ 4.7 K. From two-dimensional
powder pattern in the NMR spectrum, the ab-plane Knight shift in the normal
state was estimated by the magnetic field dependence of second-order quadrupole
shifts at various temperatures. Below 50 K, the Knight shift shows a
Curie-Weiss-like temperature dependence, similarly to the bulk magnetic
susceptibility chi. From the analysis of so-called K-chi plot, the spin and the
orbital components of K and the positive hyperfine coupling constant were
estimated. The onset temperature of superconducting transition in the Knight
shift does not change so much in an applied magnetic field up to 7 T, which is
consistent with the reported high upper critical field Hc2. The Knight shift at
7 T shows an invariant behavior below Tc. No coherence peak just below Tc was
observed in the temperature dependence of the nuclear spin-lattice relaxation
rate 1/T1 in both cases of NMR and NQR. We conclude that the invariant behavior
of the Knight shift below Tc and unconventional behaviors of 1/T possibly
indicate the spin-triplet superconductivity with p- or f-wave symmetry.Comment: 17 pages, 10 figures. Extended versio
Interplay between quantum criticality and geometrical frustration in Fe3Mo3N with stella quadrangula lattice
In the eta-carbide-type correlated-electron metal Fe3Mo3N, ferromagnetism is
abruptly induced from a nonmagnetic non-Fermi-liquid ground state either when a
magnetic field (~14 T) applied to it or when it is doped with a slight amount
of impurity (~5% Co). We observed a peak in the paramagnetic neutron scattering
intensity at finite wave vectors, revealing the presence of the
antiferromagnetic (AF) correlation hidden in the magnetic measurements. It
causes a new type of geometrical frustration in the stellla quadrangula lattice
of the Fe sublattice. We propose that the frustrated AF correlation suppresses
the F correlation to its marginal point and is therfore responsible for the
origin of the ferromagnetic (F) quantum critical behavior in pure Fe3Mo3N
Non-Detection of Gravitationally Redshifted Absorption Lines in the X-ray Burst Spectra of GS 1826-24
During a 200 ks observation with the XMM-Newton Reflection Grating
Spectrometer, we detected 16 type-I X-ray bursts from GS 1826-24. We combined
the burst spectra in an attempt to measure the gravitational redshifts from the
surface of the neutron star. We divided the composite GS 1826-24 burst spectrum
into three groups based on the blackbody temperature during the bursts. The
spectra do not show any obvious discrete absorption lines. We compare our
observations with those of EXO 0748-676.Comment: 4 pages, 4 figures; accepted for publication in ApJ
Structural phase transitions in multipole traps
A small number of laser-cooled ions trapped in a linear radiofrequency
multipole trap forms a hollow tube structure. We have studied, by means of
molecular dynamics simulations, the structural transition from a double ring to
a single ring of ions. We show that the single-ring configuration has the
advantage to inhibit the thermal transfer from the rf-excited radial components
of the motion to the axial component, allowing to reach the Doppler limit
temperature along the direction of the trap axis. Once cooled in this
particular configuration, the ions experience an angular dependency of the
confinement if the local adiabaticity parameter exceeds the empirical limit.
Bunching of the ion structures can then be observed and an analytic expression
is proposed to take into account for this behaviour
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