479 research outputs found
Spin wave spectrum of the quantum ferromagnet on the pyrochlore lattice Lu2V2O7
Neutron inelastic scattering has been used to probe the spin dynamics of the
quantum (S=1/2) ferromagnet on the pyrochlore lattice Lu2V2O7. Well-defined
spin waves are observed at all energies and wavevectors, allowing us to
determine the parameters of the Hamiltonian of the system. The data are found
to be in excellent overall agreement with a minimal model that includes a
nearest- neighbour Heisenberg exchange J = 8:22(2) meV and a
Dzyaloshinskii-Moriya interaction (DMI) D =1:5(1) meV. The large DMI term
revealed by our study is broadly consistent with the model developed by Onose
et al. to explain the magnon Hall effect they observed in Lu2V2O7 [1], although
our ratio of D=J = 0:18(1) is roughly half of their value and three times
larger than calculated by ab initio methods [2].Comment: 5 pages, 4 figure
Experimental Proof of a Magnetic Coulomb Phase
Spin ice materials are magnetic substances in which the spin directions map
onto hydrogen positions in water ice. Recently this analogy has been elevated
to an electromagnetic equivalence, indicating that the spin ice state is a
Coulomb phase, with magnetic monopole excitations analogous to ice's mobile
ionic defects. No Coulomb phase has yet been proved in a real magnetic
material, as the key experimental signature is difficult to resolve in most
systems. Here we measure the scattering of polarised neutrons from the
prototypical spin ice Ho2Ti2O7. This enables us to separate different
contributions to the magnetic correlations to clearly demonstrate the existence
of an almost perfect Coulomb phase in this material. The temperature dependence
of the scattering is consistent with the existence of deconfined magnetic
monopoles connected by Dirac strings of divergent length.Comment: 18 pages, 4 fig
The J_{eff}=1/2 insulator Sr3Ir2O7 studied by means of angle-resolved photoemission spectroscopy
The low-energy electronic structure of the J_{eff}=1/2 spin-orbit insulator
Sr3Ir2O7 has been studied by means of angle-resolved photoemission
spectroscopy. A comparison of the results for bilayer Sr3Ir2O7 with available
literature data for the related single-layer compound Sr2IrO4 reveals
qualitative similarities and similar J_{eff}=1/2 bandwidths for the two
materials, but also pronounced differences in the distribution of the spectral
weight. In particuar, photoemission from the J_{eff}=1/2 states appears to be
suppressed. Yet, it is found that the Sr3Ir2O7 data are in overall better
agreement with band-structure calculations than the data for Sr2IrO4.Comment: 5 pages, 3 figure
Electric field control of multiferroic domains in NiVO imaged by X-ray polarization enhanced topography
The magnetic structure of multiferroic NiVO has been investigated
using non-resonant X-ray magnetic scattering. Incident circularly polarized
X-rays combined with full polarization analysis of the scattered beam is shown
to yield high sensitivity to the components of the cycloidal magnetic order,
including their relative phases. New information on the magnetic structure in
the ferroelectric phase is obtained, where it is found that the magnetic
moments on the "cross-tie" sites are quenched relative to those on the "spine"
sites. This implies that the onset of ferroelectricity is associated mainly
with spine site magnetic order. We also demonstrate that our technique enables
the imaging of multiferroic domains through polarization enhanced topography.
This approach is used to image the domains as the sample is cycled by an
electric field through its hysteresis loop, revealing the gradual switching of
domains without nucleation.Comment: 9 pages, 6 figure
Bound states and field-polarized Haldane modes in a quantum spin ladder
The challenge of one-dimensional systems is to understand their physics
beyond the level of known elementary excitations. By high-resolution neutron
spectroscopy in a quantum spin ladder material, we probe the leading
multiparticle excitation by characterizing the two-magnon bound state at zero
field. By applying high magnetic fields, we create and select the singlet
(longitudinal) and triplet (transverse) excitations of the fully spin-polarized
ladder, which have not been observed previously and are close analogs of the
modes anticipated in a polarized Haldane chain. Theoretical modelling of the
dynamical response demonstrates our complete quantitative understanding of
these states.Comment: 6 pages, 3 figures plus supplementary material 7 pages 5 figure
Influence of static Jahn-Teller distortion on the magnetic excitation spectrum of PrO2: A synchrotron x-ray and neutron inelastic scattering study
A synchrotron x-ray diffraction study of the crystallographic structure of
PrO2 in the Jahn-Teller distorted phase is reported. The distortion of the
oxygen sublattice, which was previously ambiguous, is shown to be a chiral
structure in which neighbouring oxygen chains have opposite chiralities. A
temperature dependent study of the magnetic excitation spectrum, probed by
neutron inelastic scattering, is also reported. Changes in the energies and
relative intensities of the crystal field transitions provide an insight into
the interplay between the static and dynamic Jahn-Teller effects.Comment: 7 pages, 6 figure
Thermodynamics of the Spin Luttinger-Liquid in a Model Ladder Material
The phase diagram in temperature and magnetic field of the metal-organic,
two-leg, spin-ladder compound (C5H12N)2CuBr4 is studied by measurements of the
specific heat and the magnetocaloric effect. We demonstrate the presence of an
extended spin Luttinger-liquid phase between two field-induced quantum critical
points and over a broad range of temperature. Based on an ideal spin-ladder
Hamiltonian, comprehensive numerical modelling of the ladder specific heat
yields excellent quantitative agreement with the experimental data across the
complete phase diagram.Comment: 4 pages, 4 figures, updated refs and minor changes to the text,
version accepted for publication in Phys. Rev. Let
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