773 research outputs found
Doping influence of spin dynamics and magnetoelectric effect in hexagonal YLuMnO
We use inelastic neutron scattering to study spin waves and their correlation
with the magnetoelectric effect in YLuMnO. In the undoped
YMnO and LuMnO, the Mn trimerization distortion has been suggested to
play a key role in determining the magnetic structure and the magnetoelectric
effect. In YLuMnO, we find a much smaller in-plane
(hexagonal -plane) single ion anisotropy gap that coincides with a weaker
in-plane dielectric anomaly at . Since both the smaller in-plane
anisotropy gap and the weaker in-plane dielectric anomaly are coupled to a
weaker Mn trimerization distortion in YLuMnO comparing to
YMnO and LuMnO, we conclude that the Mn trimerization is responsible
for the magnetoelectric effect and multiferroic phenomenon in
YLuMnO.Comment: 5 pages, 5 figure
MCViNE -- An object oriented Monte Carlo neutron ray tracing simulation package
MCViNE (Monte-Carlo VIrtual Neutron Experiment) is a versatile Monte Carlo
(MC) neutron ray-tracing program that provides researchers with tools for
performing computer modeling and simulations that mirror real neutron
scattering experiments. By adopting modern software engineering practices such
as using composite and visitor design patterns for representing and accessing
neutron scatterers, and using recursive algorithms for multiple scattering,
MCViNE is flexible enough to handle sophisticated neutron scattering problems
including, for example, neutron detection by complex detector systems, and
single and multiple scattering events in a variety of samples and sample
environments. In addition, MCViNE can take advantage of simulation components
in linear-chain-based MC ray tracing packages widely used in instrument design
and optimization, as well as NumPy-based components that make prototypes useful
and easy to develop. These developments have enabled us to carry out detailed
simulations of neutron scattering experiments with non-trivial samples in
time-of-flight inelastic instruments at the Spallation Neutron Source. Examples
of such simulations for powder and single-crystal samples with various
scattering kernels, including kernels for phonon and magnon scattering, are
presented. With simulations that closely reproduce experimental results,
scattering mechanisms can be turned on and off to determine how they contribute
to the measured scattering intensities, improving our understanding of the
underlying physics.Comment: 34 pages, 14 figure
Interplay Between Magnetic Frustration and Quantum Criticality in the Unconventional Ladder Antiferromagnet C9H18N2CuBr4
Quantum fluctuation in frustrated magnets and quantum criticality at the
transition between different quantum phases of matter are two of the
cornerstones in condensed matter physics. Here we demonstrate the nontrivial
interplay between them in the spin-1/2 coupled two-leg ladder antiferromagnet
C9H18N2CuBr4. Employing the high-resolution neutron spectroscopy, we
unambiguously identify a weakly first-order hydrostatic pressure-driven quantum
phase transition, which arises from fluctuations enhanced by the frustrating
interlayer coupling. An exotic pressure-induced quantum disordered state is
evidenced by the broad spectral linewidth observed near the phase transition.
Interestingly, we find that the gapped transverse excitations in the
Neel-ordered phase at ambient pressure cannot be described by the conventional
S=1 magnons, i.e., the spin wave quanta, associated with explicit symmetry
breaking, and thus the three-dimensional magnetic order ought to emerge in an
unconventional way. We further apply the quantum Fisher information to show the
presence of bipartite entanglement at criticality at least up to 1.1 K in the
same material.Comment: 10 pages and 6 figures. We call for theoretical understanding of the
nontrivial interplay observed in this materia
Neutron spin resonance as a probe of Fermi surface nesting and superconducting gap symmetry in BaK(FeCo)As
We use inelastic neutron scattering to study energy and wave vector
dependence of the superconductivity-induced resonance in hole-doped
BaK(FeCo)As ( with
K, respectively). In previous work on electron-doped
Ba(FeNi)As ( K and K), the
resonance is found to peak sharply at the antiferromagnetic (AF) ordering wave
vector along the longitudinal direction, but disperses
upwards away from along the transverse direction. For hole
doped without AF order, we find that the resonance displays
ring-like upward dispersion away from along both the
longitudinal and transverse directions. By comparing these results with
calculations using the random phase approximation, we conclude that the
dispersive resonance is a direct signature of isotropic superconducting gaps
arising from nested hole-electron Fermi surfaces.Comment: 5 pages, 4 figure
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