145 research outputs found
Excitations in the ordered and paramagnetic states of honeycomb magnet Na2Co2TeO6
Na2Co2TeO6 is a proposed approximate Kitaev magnet, yet its actual magnetic
interactions are elusive due to a lack of knowledge on the full excitation
spectrum. Here, using inelastic neutron scattering and single crystals, we
determine the system's temperature-dependent magnetic excitations over the
entire Brillouin zone. Without committing to specific models, we unveil a
distinct signature of the third-nearest-neighbor coupling in the spin waves,
which signifies the associated distance as an emerging "soft link" in the
ordered state. The presence of at least six non-overlapping spin-wave branches
is at odds with all models proposed to date. Above the ordering temperature,
persisting dynamic correlations can be described by equal-time magnetic
structure factors of a hexagonal cluster, which reveal the leading
instabilities. Our result sets definitive constraint on theoretical models for
Na2Co2TeO6 and provides new insight for the materialization of the Kitaev
model.Comment: 4 pages, 4 figures plus Supplemental Material; comments are welcom
Magnetic properties of the Ag-In-rare-earth 1/1 approximants
We have performed magnetic susceptibility and neutron scattering measurements
on polycrystalline Ag-In-RE (RE: rare-earth) 1/1 approximants. In the magnetic
susceptibility measurements, for most of the RE elements, inverse
susceptibility shows linear behaviour in a wide temperature range, confirming
well localized isotropic moments for the RE ions. Exceptionally for the
light RE elements, such as Ce and Pr, non-linear behaviour was observed,
possibly due to significant crystalline field splitting or valence fluctuation.
For RE = Tb, the susceptibility measurement clearly shows a bifurcation of the
field-cooled and zero-field-cooled susceptibility at ~K,
suggesting a spin-glass-like freezing. On the other hand, neutron scattering
measurements detect significant development of short-range antiferromagnetic
spin correlations in elastic channel, which accompanied by a broad peak at
~meV in inelastic scattering spectrum. These features have
striking similarity to those in the Zn-Mg-Tb quasicrystals, suggesting that the
short-range spin freezing behaviour is due to local high symmetry clusters
commonly seen in both the systems.Comment: 14 pages, 12 figure
Neutron scattering study on spin correlations and fluctuations in the transition-metal-based magnetic quasicrystal Zn-Fe-Sc
Spin correlations and fluctuations in the 3d-transition-metal-based
icosahedral quasicrystal Zn-Fe-Sc have been investigated by neutron scattering
using polycrystalline samples. Magnetic diffuse scattering has been observed in
the elastic experiment at low temperatures, indicating development of static
short-range-spin correlations. In addition, the inelastic scattering experiment
detects a -independent quasielastic signal ascribed to single-site
relaxational spin fluctuations. Above the macroscopic freezing temperature
K, the spin relaxation rate shows Arrhenius-type behavior,
indicating thermally activated relaxation process. In contrast, the relaxation
rate remains finite even at the lowest temperature, suggesting a certain
quantum origin for the spin fluctuations below .Comment: To be published in Phys. Rev.
Renormalization of spin excitations in hexagonal HoMnO3 by magnon-phonon coupling
Hexagonal HoMnO3, a two-dimensional Heisenberg antiferromagnet, has been
studied via inelastic neutron scattering. A simple Heisenberg model with a
single-ion anisotropy describes most features of the spin-wave dispersion
curves. However, there is shown to be a renormalization of the magnon energies
located at around 11 meV. Since both the magnon-magnon interaction and
magnon-phonon coupling can affect the renormalization in a noncollinear magnet,
we have accounted for both of these couplings by using a Heisenberg XXZ model
with 1=S expansions [1] and the Einstein site phonon model [13], respectively.
This quantitative analysis leads to the conclusion that the renormalization
effect primarily originates from the magnon-phonon coupling, while the
spontaneous magnon decay due to the magnon-magnon interaction is suppressed by
strong two-ion anisotropy.Comment: 5 pages, 4 figure
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