201 research outputs found
Spin-wave spectrum of copper metaborate in the commensurate phase 10K<T<21K
We have investigated the spin-wave spectrum of copper metaborate,
CuBO, by means of inelastic neutron scattering in the commensurate
magnetic phase. We have found two branches of spin-wave excitations associated
with the two magnetic sublattices Cu(A) and Cu(B), respectively. In the
temperature regime , where only the Cu(A) magnetic moments
are ordered, the interaction between the two sublattices is found to be
negligible. With this approximation we have determined the `easy plane'
exchange parameters of the Cu(A) subsystem within standard spin-wave theory.Comment: 4 figure
Synthesis and structural characterization of 2Dioxane.2H2O.CuCl2: metal-organic compound with Heisenberg antiferromagnetic S=1/2 chains
A novel organometallic compound 2Dioxane.CuCl2.2H2O has been synthesized and
structurally characterized by X-ray crystallography. Magnetic susceptibility
and zero-field inelastic neutron scattering have also been used to study its
magnetic properties. It turns out that this material is a weakly coupled
one-dimensional S=1/2 Heisenberg antiferromagnetic chain system with chain
direction along the crystallographic c axis and the nearest-neighbor
intra-chain exchange constant J=0.85(4) meV. The next-nearest-neighbor
inter-chain exchange constant J' is also estimated to be 0.05 meV. The observed
magnetic excitation spectrum from inelastic neutron scattering is in excellent
agreement with numerical calculations based on the Muller ansatz.Comment: 4 pages; 5 figure
Anomalous pressure dependence of the atomic displacements in the relaxor ferroelectric PbMgTaO
The crystal structure of the PbMgTaO (PMT) relaxor
ferroelectric was studied under hydrostatic pressure up to GPa by
means of powder neutron diffraction. We find a drastic pressure-induced
decrease of the lead displacement from the inversion centre which correlates
with an increase by 50 % of the anisotropy of the oxygen temperature
factor. The vibrations of the Mg/Ta are, in contrast, rather pressure
insensitive. We attribute these changes being responsible for the previously
reported pressure-induced suppression of the anomalous dielectric permittivity
and diffuse scattering in relaxor ferroelectrics
Observation of plaquette fluctuations in the spin-1/2 honeycomb lattice
Quantum spin liquids are materials that feature quantum entangled spin
correlations and avoid magnetic long-range order at T = 0 K. Particularly
interesting are two-dimensional honeycomb spin lattices where a plethora of
exotic quantum spin liquids have been predicted. Here, we experimentally study
an effective S=1/2 Heisenberg honeycomb lattice with competing nearest and
next-nearest neighbor interactions. We demonstrate that YbBr avoids order
down to at least T=100 mK and features a dynamic spin-spin correlation function
with broad continuum scattering typical of quantum spin liquids near a quantum
critical point. The continuum in the spin spectrum is consistent with plaquette
type fluctuations predicted by theory. Our study is the experimental
demonstration that strong quantum fluctuations can exist on the honeycomb
lattice even in the absence of Kitaev-type interactions, and opens a new
perspective on quantum spin liquids.Comment: 32 pages, 7 Figure
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