144 research outputs found
Magnetic shape-memory effect in SrRuO
Like most perovskites, SrRuO exhibits structural phase transitions
associated with rotations of the RuO octahedra. The application of moderate
magnetic fields in the ferromagnetically ordered state allows one to fully
control these structural distortions, although the ferromagnetic order occurs
at six times lower temperature than the structural distortion. Our neutron
diffraction and macroscopic measurements unambiguously show that magnetic
fields rearrange structural domains, and that for the field along a cubic
[110] direction a fully detwinned crystal is obtained. Subsequent heating
above the Curie temperature causes a magnetic shape-memory effect, where the
initial structural domains recover
Low-energy excitations in the magnetized state of the bond-alternating quantum S=1 chain system NTENP
High intensity inelastic neutron scattering experiments on the S=1
quasi-one-dimensional bond-alternating antiferromagnet Ni(C9D24N4)(NO2)ClO4
(NTENP) are performed in magnetic fields of up to 14.8~T. Excitation in the
high field magnetized quantum spin solid (ordered) phase are investigated. In
addition to the previously observed coherent long-lived gap excitation [M.
Hagiwara et al., Phys. Rev. Lett 94, 177202 (2005)], a broad continuum is
detected at lower energies. This observation is consistent with recent
numerical studies, and helps explain the suppression of the lowest-energy gap
mode in the magnetized state of NTENP. Yet another new feature of the
excitation spectrum is found at slightly higher energies, and appears to be
some kind of multi-magnon state.Comment: 5 pages, 4 fugure
Fractional spinon excitations in the quantum Heisenberg antiferromagnetic chain
Assemblies of interacting quantum particles often surprise us with properties
that are difficult to predict. One of the simplest quantum many-body systems is
the spin 1/2 Heisenberg antiferromagnetic chain, a linear array of interacting
magnetic moments. Its exact ground state is a macroscopic singlet entangling
all spins in the chain. Its elementary excitations, called spinons, are
fractional spin 1/2 quasiparticles; they are created and detected in pairs by
neutron scattering. Theoretical predictions show that two-spinon states exhaust
only 71% of the spectral weight while higher-order spinon states, yet to be
experimentally located, are predicted to participate in the remaining. Here, by
accurate absolute normalization of our inelastic neutron scattering data on a
compound realizing the model, we account for the full spectral weight to within
99(8)%. Our data thus establish and quantify the existence of higher-order
spinon states. The observation that within error bars, the entire weight is
confined within the boundaries of the two-spinon continuum, and that the
lineshape resembles a rescaled two-spinon one, allow us to develop a simple
physical picture for understanding multi-spinon excitations.Comment: 22 pages, 4 figures, Supplementary material
Spin gaps and magnetic structure of NaxCoO2
We present two experiments that provide information on spin anisotropy and
the magnetic structure of NaxCoO2. First, we report low-energy neutron
inelastic scattering measurements of the zone-center magnetic excitations in
the magnetically ordered phase of Na0.75CoO2. The energy spectra suggest the
existence of two gaps, and are very well fitted by a spin-wave model with both
in-plane and out-of-plane anisotropy terms. The gap energies decrease with
increasing temperature and both gaps are found to have closed when the
temperature exceeds the magnetic ordering temperature T_m~22 K. Secondly, we
present neutron diffraction studies of Na0.85CoO2 with a magnetic field applied
approximately parallel to the c axis. For fields in excess of ~8T a magnetic
Bragg peak was observed at the (0,0,3) position in reciprocal space. We
interpret this as a spin-flop transition of the A-type antiferromagnetic
structure, and we show that the spin-flop field is consistent with the size of
the anisotropy gap.Comment: 9 pages, 7 figure
Spin Susceptibility of the Topological Superconductor UPt3 from Polarized Neutron Diffraction
Experiment and theory indicate that UPt3 is a topological superconductor in
an odd-parity state, based in part from temperature independence of the NMR
Knight shift. However, quasiparticle spin-flip scattering near a surface, where
the Knight shift is measured, might be responsible. We use polarized neutron
scattering to measure the bulk susceptibility with H||c, finding consistency
with the Knight shift but inconsistent with theory for this field orientation.
We infer that neither spin susceptibility nor Knight shift are a reliable
indication of odd-parity
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