131 research outputs found
The magnetic exchange parameters and anisotropy of the quasi-two dimensional antiferromagnet NiPS
Neutron inelastic scattering has been used to measure the magnetic
excitations in powdered NiPS, a quasi-two dimensional antiferromagnet with
spin on a honeycomb lattice. The spectra show clear, dispersive magnons
with a meV gap at the Brillouin zone center. The data were fitted
using a Heisenberg Hamiltonian with a single-ion anisotropy assuming no
magnetic exchange between the honeycomb planes. Magnetic exchange interactions
up to the third intraplanar nearest-neighbour were required. The fits show
robustly that NiPS has an easy axis anisotropy with meV and
that the third nearest-neighbour has a strong antiferromagnetic exchange of
meV. The data can be fitted reasonably well with either
or , however the best quantitative agreement with high-resolution data
indicate that the nearest-neighbour interaction is ferromagnetic with meV and that the second nearest-neighbour exchange is small and
antiferromagnetic with meV. The dispersion has a minimum in the
Brillouin zone corner that is slightly larger than that at the Brillouin zone
center, indicating that the magnetic structure of NiPS is close to being
unstable.Comment: 21 pages, 7 figures, 33 reference
Magnetic Excitations of Undoped Iron Oxypnictides
We study the magnetic excitations of undoped iron oxypnictides using a
three-dimensional Heisenberg model with single-ion anisotropy. Analytic forms
of the spin wave dispersion, velocities, and structure factor are given. Aside
from quantitative comparisons which can be made to inelastic neutron scattering
experiments, we also give qualitative criteria which can distinguish various
regimes of coupling strength. The magnetization reduction due to quantum zero
point fluctuations shows clear dependence on the c-axis coupling.Comment: 4 pages, 5 figures, to appear in Frontiers of Physics in China: a
special issue on Iron-based superconductor
Investigation of the dynamics of 1-octene adsorption at 293 K in a ZSM-5 catalyst by inelastic and quasielastic neutron scattering
The properties of 1-octene adsorbed in zeolite ZSM-5 at 293 K are studied by means of inelastic and quasielastic neutron scattering (INS and QENS) in order to investigate interactions relevant to the zeolite solid acid catalysis of fluidised catalytic cracking reactions. The INS spectrum is compared to that recorded for the solid alkene and reveals significant changes of bonding on adsorption at ambient temperatures; the changes are attributed to the oligomerization of the adsorbed 1-octene to form a medium chain n-alkane or n-alkane cation. QENS analysis shows that these oligomers are immobilised within the zeolite pore structure but a temperature-dependant fraction is able to rotate around their long axis within the pore channels
Simulation-based training can improve on-call physiotherapists’ clinical reasoning abilities and self-reported competency
X-ray Resonant Scattering Study of the Order Parameters in Multiferroic TbMnO
We report on an extensive investigation of the multiferroic compound
TbMnO. Non-resonant x-ray magnetic scattering (NRXMS) revealed a dominant
-type domain. The temperature dependence of the intensity and wavevector
associated with the incommensurate magnetic order was found to be in good
agreement with neutron scattering data. XRS experiments were performed in the
vicinity of the Mn and Tb edges in the high-temperature collinear
phase, the intermediate temperature cycloidal/ferroelectric phase, and the
low-temperature phase. In the collinear phase resonant satellites were
found at the Mn edge associated with -type but also -type peaks. The
azimuthal dependence of the -type satellites (and their absence in the NRXMS
experiments) indicates that they are most likely non-magnetic in origin. We
suggest instead that they may be associated with an induced charge multipole.
At the Tb edge resonant - and -type satellites () were
observed in the collinear phase. These we attribute to a polarisation of the Tb
5 states by the ordering of the Mn sublattice. In the
cycloidal/ferroelectric phase a new set of resonant satellites appear
corresponding to -type order. These appear at the Tb edge only. In
addition to a dominant component in the channel, a
weaker component is found in the pre-edge with
polarization. Calculations of the XRS were performed using the code
showing that the unrotated component of the Tb
-type peaks appearing in the ferroelectric phase contains a contribution
from a multipole that is odd with respect to both space and time, known in
various contexts as the anapole.Comment: Phys. Rev. B (In press
An x-ray resonant diffraction study of multiferroic DyMn2O5
X-ray resonant scattering has been used to measure the magnetic order of the
Dy ions below 40K in multiferroic DyMnO. The magnetic order has a
complex behaviour. There are several different ordering wavevectors, both
incommensurate and commensurate, as the temperature is varied. In addition a
non-magnetic signal at twice the wavevector of one of the commensurate signals
is observed, the maximum intensity of which occurs at the same temperature as a
local maximum in the ferroelectric polarisation. Some of the results, which
bear resemblence to the behaviour of other members of the RMnO
family of multiferroic materials, may be explained by a theory based on
so-called acentric spin-density waves.Comment: 8 pages, 8 figure
Normal State Spin Dynamics of Five-band Model for Iron-pnictides
Normal state spin dynamics of the recently discovered iron-pnictide
superconductors is discussed by calculating spin structure factor S(q, omega)
in an itinerant five-band model within RPA approximation. Due to the
characteristic Fermi surface structure of iron-pnictide, column like response
is found at (pi, 0) in extended Brillouin zone in the undoped case, which is
consistent with the recent neutron scattering experiment. This indicates that
the localized spin model is not necessary to explain the spin dynamics of this
system. Furthermore, we show that the temperature dependence of inelastic
neutron scattering intensity can be well reproduced in the itinerant model. We
also study NMR 1/T_1T in the same footing calculation and show that the
itinerant model can capture the magnetic property of iron-pnictide
superconductors.Comment: 4 page
Nature of the magnetic order in the charge-ordered cuprate La1.48Nd0.4Sr0.12CuO4
Using polarized neutron scattering we establish that the magnetic order in La1.48Nd0.4Sr0.12CuO4 is either (i) one dimensionally modulated and collinear, consistent with the stripe model or (ii) two dimensionally modulated with a novel noncollinear structure. The measurements rule out a number of alternative models characterized by 2D electronic order or 1D helical spin order. The low-energy spin excitations are found to be primarily transversely polarized relative to the stripe ordered state, consistent with conventional spin waves
- …