784 research outputs found
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
Superconducting nanowire single-photon detectors with non-periodic dielectric multilayers
We present superconducting nanowire single-photon detectors (SSPDs) on non-periodic dielectric multilayers, which enable us to design a variety of wavelength dependences of optical absorptance by optimizing the dielectric multilayer. By adopting a robust simulation to optimize the dielectric multilayer, we designed three types of SSPDs with target wavelengths of 500 nm, 800 nm, and telecom range respectively. We fabricated SSPDs based on the optimized designs for 500 and 800 nm, and evaluated the system detection efficiency at various wavelengths. The results obtained confirm that the designed SSPDs with non-periodic dielectric multilayers worked well. This versatile device structure can be effective for multidisciplinary applications in fields such as the life sciences and remote sensing that require high efficiency over a precise spectral range and strong signal rejection at other wavelengths
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
Mn-doping-induced itinerant-electron ferromagnetism in Cr[2]GeC
The magnetism of the M[n+1]AXn phase, Cr[2]GeC, and its Mn-doped system, (Cr[1−x]Mn[x])[2]GeC (x≤0.25), synthesized via a solid state reaction, was investigated systematically. Cr[2]GeC is in a spin-unpolarized state, but the ferromagnetic band polarization is induced immediately by the Mn doping. The Curie temperature, TC, and the spontaneous moment, ps, increase almost proportionally to the Mn concentration, strongly suggesting that Cr[2]GeC is located in the vicinity of a ferromagnetic quantum critical point. The strong concentration dependence of p[eff]/p[s], where p[eff] is the effective moment in the paramagnetic state, indicates that the ferromagnetism appearing in the Mn-doped Cr[2]GeC can be classified as a typical itinerant-electron ferromagnetism in a wide range of the degree of electron localization
Anomalous phase of MnP at very low field
Manganese phosphide MnP has been investigated for decades because of its rich
magnetic phase diagram. It is well known that the MnP exhibits the
ferromagnetic phase transition at \Tc=292 K and the helical magnetic phase
below \TN=47 K at zero field. Recently, a novel magnetic phase transition was
observed at K when the magnetic field is lower than 5 Oe. However,
the nature of the new phase has not been illuminated yet. In order to reveal
it, we performed the AC and the DC magnetization measurements for a single
crystal MnP at very low field. A divergent behavior of the real and the
imaginary part of the AC susceptibility and a sharp increase of the DC
magnetization was observed at , indicating the magnetic phase transition
at . Furthermore a peculiar temperature hysteresis was observed: namely,
the magnetization depends on whether cooling sample to the temperature lower
than \TN or not before the measurements. This hysteresis phenomenon suggests
the complicated nature of the new phase and a strong relation between the
magnetic state of the new phase and the helical structure.Comment: 4 pages, 2 figure
A new double-layered kagome antiferromagnet ScFeGe
ScFeGe with the LiFeGe-type structure (space group
), which has a double-layered kagome lattice (18 site) of Fe
crystallographically equivalent to that of a well-known topological ferromagnet
FeSn, is newly found to be antiferromagnetic (AFM) with a high N\'eel
temperature of K, in contrast to the ferromagnetic
(FM) ground state previously proposed in a literature. Sc nuclear
magnetic resonance experiment revealed the absence of a hyperfine field at the
Sc site, providing microscopic evidence for the AFM state and indicating AFM
coupling between the bilayer kagome blocks. The stability of the AFM structure
under the assumption of FM intra-bilayer coupling is verified by DFT
calculations.Comment: 13 pages, 1 tables, 4 figure
Strong-field general relativity and quasi-periodic oscillations in x-ray binaries
Quasi-periodic oscillations (QPOs) at frequencies near 1000 Hz were recently
discovered in several x-ray binaries containing neutron stars. Two sources show
no correlation between QPO frequency and source count rate (Berger et al. 1996,
Zhang et al. 1996). We suggest that the QPO frequency is determined by the
Keplerian orbital frequency near the marginally stable orbit predicted by
general relativity in strong gravitational fields (Muchotrzeb-Czerny 1986,
Paczynski 1987, Kluzniak et al. 1990). The QPO frequencies observed from 4U
1636-536 imply that the mass of the neutron star is 2.02 +/- 0.12 solar masses.
Interpretation of the 4.1 keV absorption line observed from 4U 1636-536 (Waki
et al. 1984) as due to Fe XXV ions then implies a neutron star radius of 9.6
+/-0.6 km.Comment: 4 pages, uses aas2pp4.sty, submitted to ApJ
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
- …