1,325 research outputs found
Spin reorientation transition in the incommensurate stripe-ordered phase of La3/2Sr1/2NiO4
The spin ordering of La3/2Sr1/2NiO4 was investigated by magnetization
measurements, and by unpolarized- and polarized-neutron diffraction. Spin
ordering with an incommensurability epsilon ~ 0.445 is observed below T_so ~ 80
K. On cooling, a spin reorientation is observed at 57 +/- 1 K, with the spin
axes rotating from 52 +/- 4 degrees to 78 +/- 3 degrees. This is the first time
a spin reorientation has been observed in a La2-xSrxNiO4+delta compound having
incommensurate stripe order.Comment: REVTex 4. 4 pages including 4 figures. Minor changes to text.
Accepted to be published in Physical Review
Haydeeite: a spin-1/2 kagome ferromagnet
The mineral haydeeite, alpha-MgCu3(OD)6Cl2, is a S=1/2 kagome ferromagnet
that displays long-range magnetic order below TC=4.2 K with a strongly reduced
moment. Our inelastic neutron scattering data show clear spin-wave excitations
that are well described by a Heisenberg Hamiltonian with ferromagnetic
nearest-neighbor exchange J1=-38 K and antiferromagnetic exchange Jd=+11 K
across the hexagons of the kagome lattice. These values place haydeeite very
close to the quantum phase transition between ferromagnetic order and
non-coplanar twelve-sublattice cuboc2 antiferromagnetic order. Diffuse dynamic
short-range ferromagnetic correlations observed above TC persist well into the
ferromagnetically ordered phase with a behavior distinct from critical
scattering
Low dimensional ordering and fluctuations in methanol--hydroquinone-clathrate studied by X-ray and neutron diffraction
Methanol--hydroquinone-clathrate has been established as a model
system for dielectric ordering and fluctuations and is conceptually close to
magnetic spin systems. In X-ray and neutron diffraction experiments, we
investigated the ordered structure, the one-dimensional (1D) and the
three-dimensional (3D) critical scattering in the paraelectric phase, and the
temperature dependence of the lattice constants. Our results can be explained
by microscopic models of the methanol pseudospin in the hydroquinone cage
network, in consistency with previous dielectric investigations
Magnetic Order and Dynamics in Stripe-Ordered La2-xSrxNiO4
We have studied magnetic correlations in several compositions of
stripe-ordered La2-xSrxNiO4. In this paper we show how polarized-neutron
scattering has helped uncover important features of the magnetic ordering and
spin dynamics. In particular, polarization analysis has enabled us (1) to
characterize a spin reorientation transition, (2) to identify anisotropy gaps
in the spin excitation spectrum, and (3) to investigate an anomalous dip in the
spin-wave intensity suggestive of coupling between collective spin and charge
excitations.Comment: 4 pages, 3 figs. Presented at PNSXM, Venice. To appear in Physica
Electronic structure and magnetic properties of the spin-1/2 Heisenberg system CuSe2O5
A microscopic magnetic model for the spin-1/2 Heisenberg chain compound
CuSe2O5 is developed based on the results of a joint experimental and
theoretical study. Magnetic susceptibility and specific heat data give evidence
for quasi-1D magnetism with leading antiferromagnetic (AFM) couplings and an
AFM ordering temperature of 17 K. For microscopic insight, full-potential DFT
calculations within the local density approximation (LDA) were performed. Using
the resulting band structure, a consistent set of transfer integrals for an
effective one-band tight-binding model was obtained. Electronic correlations
were treated on a mean-field level starting from LDA (LSDA+U method) and on a
model level (Hubbard model). In excellent agreement of experiment and theory,
we find that only two couplings in CuSe2O5 are relevant: the nearest-neighbour
intra-chain interaction of 165 K and a non-frustrated inter-chain coupling of
20 K. From a comparison with structurally related systems (Sr2Cu(PO4)2,
Bi2CuO4), general implications for a magnetic ordering in presence of
inter-chain frustration are made.Comment: 20 pages, 8 figures, 3 table
Spin correlations among the charge carriers in an ordered stripe phase
We have observed a diffuse component to the low-energy magnetic excitation
spectrum of stripe-ordered La5/3Sr1/3NiO4 probed by neutron inelastic
scattering. The diffuse scattering forms a square pattern with sides parallel
and perpendicular to the stripe directions. The signal is dispersive, with a
maximum energy of ~10 meV. Probed at 2 meV the scattering decreases in strength
with increasing temperature, and is barely visible at 100 K. We argue that the
signal originates from dynamic, quasi- one-dimensional, antiferromagnetic
correlations among the stripe electrons.Comment: 4 pages, 4 figures. To be published in Physical Review Letter
The critical behavior of frustrated spin models with noncollinear order
We study the critical behavior of frustrated spin models with noncollinear
order, including stacked triangular antiferromagnets and helimagnets. For this
purpose we compute the field-theoretic expansions at fixed dimension to six
loops and determine their large-order behavior. For the physically relevant
cases of two and three components, we show the existence of a new stable fixed
point that corresponds to the conjectured chiral universality class. This
contradicts previous three-loop field-theoretical results but is in agreement
with experiments.Comment: 4 pages, RevTe
Jahn-Teller versus quantum effects in the spin-orbital material LuVO3
We report on combined neutron and resonant x-ray scattering results,
identifying the nature of the spin-orbital ground state and magnetic
excitations in LuVO3 as driven by the orbital parameter. In particular, we
distinguish between models based on orbital Peierls dimerization, taken as a
signature of quantum effects in orbitals, and Jahn-Teller distortions, in favor
of the latter. In order to solve this long-standing puzzle, polarized neutron
beams were employed as a prerequisite in order to solve details of the magnetic
structure, which allowed quantitative intensity-analysis of extended magnetic
excitation data sets. The results of this detailed study enabled us to draw
definite conclusions about classical vs quantum behavior of orbitals in this
system and to discard the previous claims about quantum effects dominating the
orbital physics of LuVO3 and similar systems.Comment: Phys. Rev. B 91, 161104(R) (2015
Magnetic-field-induced spin excitations and renormalized spin gap of the underdoped superconductor LaSrCuO
High-resolution neutron inelastic scattering experiments in applied magnetic
fields have been performed on LaSrCuO (LSCO). In zero
field, the temperature dependence of the low-energy peak intensity at the
incommensurate momentum-transfer $\mathbf{Q}^{\
}_{\mathrm{IC}}=(0.5,0.5\pm\delta,0),(0.5\pm\delta,0.5,0)T^{\}_{c}$ which broadens and shifts to lower
temperature upon the application of a magnetic field along the c-axis. A
field-induced enhancement of the spectral weight is observed, but only at
finite energy transfers and in an intermediate temperature range. These
observations establish the opening of a strongly downward renormalized spin gap
in the underdoped regime of LSCO. This behavior contrasts with the observed
doping dependence of most electronic energy features.Comment: accepted for publication in Phys. Rev. Let
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