162 research outputs found
In-Situ Neutron Diffraction Under Tensile Loading of Powder-in-Tube Cu/NbSn Composite Wires: Effect of Reaction Heat Treatment on Texture, Internal Stress State and Load Transfer
The strain induced degradation of NbSn superconductors can hamper the performance of high field magnets. We report elastic strain measurements in the different phases of entire non-heat treated and fully reacted NbSn composite strands as a function of uniaxial stress during in-situ deformation under neutron beam. After the reaction heat treatment the Cu matrix loses entirely its load carrying capability and the applied stress is transferred to the remaining Nb-Ta alloy and to the brittle (Nb-Ta)3Sn phase, which exhibits a preferential grain orientation parallel to the strand axis
Correlated decay of triplet excitations in the Shastry-Sutherland compound SrCu(BO)
The temperature dependence of the gapped triplet excitations (triplons) in
the 2D Shastry-Sutherland quantum magnet SrCu(BO) is studied by
means of inelastic neutron scattering. The excitation amplitude rapidly
decreases as a function of temperature while the integrated spectral weight can
be explained by an isolated dimer model up to 10~K. Analyzing this anomalous
spectral line-shape in terms of damped harmonic oscillators shows that the
observed damping is due to a two-component process: one component remains sharp
and resolution limited while the second broadens. We explain the underlying
mechanism through a simple yet quantitatively accurate model of correlated
decay of triplons: an excited triplon is long-lived if no thermally populated
triplons are near-by but decays quickly if there are. The phenomenon is a
direct consequence of frustration induced triplon localization in the
Shastry--Sutherland lattice.Comment: 5 pages, 4 figure
Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4
We study spin liquid in the frustrated diamond lattice antiferromagnet
CoAl2O4 by means of single crystal neutron scattering in zero and applied
magnetic field. The magnetically ordered phase appearing below TN=8 K remains
nonconventional down to 1.5 K. The magnetic Bragg peaks at the q=0 positions
remain broad and their profiles have strong Lorentzian contribution.
Additionally, they are connected by weak diffuse streaks along the
directions. These observations are explained within the spiral spin liquid
model as short-range magnetic correlations of spirals populated at these finite
temperatures, as the energy minimum around q=0 is flat and the energy of
excited states with q=(111) is low. The agreement is only qualitative, leading
us to suspect that microstructure effects are also important. Magnetic field
significantly perturbs spin correlations. The 1.5 K static magnetic moment
increases from 1.58 mB/Co at zero field to 2.08 mB/Co at 10 T, while the
magnetic peaks, being still broad, acquire almost Gaussian profile. Spin
excitations are rather conventional spin waves at zero field, resulting in the
exchange parameters J1=0.92(1) meV, J2=0.101(2) meV and the anisotropy term
D=-0.0089(2) meV for CoAl2O4. The application of a magnetic field leads to a
pronounced broadening of the excitations at the zone center, which at 10 T
appear gapless and nearly featureless
Dipolar spin-waves and tunable band gap at the Dirac points in the 2D magnet ErBr3
Topological magnon insulators constitute a growing field of research for
their potential use as information carriers without heat dissipation. We report
an experimental and theoretical study of the magnetic ground-state and
excitations in the van der Waals two-dimensional honeycomb magnet ErBr3. We
show that the magnetic properties of this compound are entirely governed by the
dipolar interactions which generate a continuously degenerate non-collinear
ground-state on the honeycomb lattice with spins confined in the plane. We find
that the magnon dispersion exhibits Dirac-like cones when the magnetic moments
in the ground-state are related by time-reversal and inversion symmetries
associated with a Berry phase \pi as in single-layer graphene. A magnon band
gap opens when the dipoles are rotated away from this state, entailing a finite
Berry curvature in the vicinity of the K and K' Dirac points. Our results
illustrate that the spin-wave dispersion of dipoles on the honeycomb lattice
can be reversibly controlled from a magnetic phase with Dirac cones to a
topological antiferromagnetic insulator with non-trivial valley Chern number
Spin excitations in the skymion host Cu2OSeO3
We have used inelastic neutron scattering to measure the magnetic excitation
spectrum along the high-symmetry directions of the first Brillouin zone of the
magnetic skyrmion hosting compound CuOSeO. The majority of our
scattering data are consistent with the expectations of a recently proposed
model for the magnetic excitations in CuOSeO, and we report best-fit
parameters for the dominant exchange interactions. Important differences exist,
however, between our experimental findings and the model expectations. These
include the identification of two energy scales that likely arise due to
neglected anisotropic interactions. This feature of our work suggests that
anisotropy should be considered in future theoretical work aimed at the full
microscopic understanding of the emergence of the skyrmion state in this
material.Comment: 5 pages, 6 figure
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