446 research outputs found
Exotic magnetism on the quasi-FCC lattices of the double perovskites LaNaBO (B Ru, Os)
We find evidence for long-range and short-range ( 70 \AA~at 4 K)
incommensurate magnetic order on the quasi-face-centered-cubic (FCC) lattices
of the monoclinic double perovskites LaNaRuO and LaNaOsO
respectively. Incommensurate magnetic order on the FCC lattice has not been
predicted by mean field theory, but may arise via a delicate balance of
inequivalent nearest neighbour and next nearest neighbour exchange
interactions. In the Ru system with long-range order, inelastic neutron
scattering also reveals a spin gap 2.75 meV. Magnetic
anisotropy is generally minimized in the more familiar octahedrally-coordinated
systems, so the large gap observed for LaNaRuO may result from
the significantly enhanced value of spin-orbit coupling in this
material.Comment: 5 pages, 4 figure
The lattice Schwarzian KdV equation and its symmetries
In this paper we present a set of results on the symmetries of the lattice
Schwarzian Korteweg-de Vries (lSKdV) equation. We construct the Lie point
symmetries and, using its associated spectral problem, an infinite sequence of
generalized symmetries and master symmetries. We finally show that we can use
master symmetries of the lSKdV equation to construct non-autonomous
non-integrable generalized symmetries.Comment: 11 pages, no figures. Submitted to Jour. Phys. A, Special Issue SIDE
VI
Revisiting the ground state of CoAlO: comparison to the conventional antiferromagnet MnAlO
The A-site spinel material, CoAl2O4, is a physical realization of the
frustrated diamond-lattice antiferromagnet, a model in which is predicted to
contain unique incommensurate or `spin-spiral liquid' ground states. Our
previous single-crystal neutron scattering study instead classified it as a
`kinetically-inhibited' antiferromagnet, where the long ranged correlations of
a collinear Neel ground state are blocked by the freezing of domain wall motion
below a first-order phase transition at T* = 6.5 K. The current paper expands
on our original results in several important ways. New elastic and inelastic
neutron measurements are presented that show our initial conclusions are
affected by neither the sample measured nor the instrument resolution, while
measurements to temperatures as low as T = 250 mK limit the possible role being
played by low-lying thermal excitations. Polarized diffuse neutron measurements
confirm reports of short-range antiferromagnetic correlations and diffuse
streaks of scattering, but major diffuse features are explained as signatures
of overlapping critical correlations between neighboring Brillouin zones.
Finally, and critically, this paper presents detailed elastic and inelastic
measurements of magnetic correlations in a single-crystal of MnAl2O4, which
acts as an unfrustrated analogue to CoAl2O4. The unfrustrated material is shown
to have a classical continuous phase transition to Neel order at T_N = 39 K,
with collective spinwave excitations and Lorentzian-like critical correlations
which diverge at the transition. Direct comparison between the two compounds
indicates that CoAl2O4 is unique, not in the nature of high-temperature diffuse
correlations, but rather in the nature of the frozen state below T*. The higher
level of cation inversion in the MnAl2O4 sample indicates that this novel
behavior is primarily an effect of greater next-nearest-neighbor exchange.Comment: 13 pages, 8 figures, acccepted for publication in Physical Review
Field-induced Bose-Einstein Condensation of triplons up to 8 K in Sr3Cr2O8
Single crystals of the spin dimer system Sr3Cr2O8 have been grown for the
first time. Magnetization, heat capacity, and magnetocaloric effect data up to
65 T reveal magnetic order between applied fields of Hc1 ~ 30.4 T and Hc2 ~ 62
T. This field-induced order persists up to ~ 8 K at H ~ 44 T, the highest
observed in any quantum magnet where Hc2 is experimentally-accessible. We fit
the temperature-field phase diagram boundary close to Hc1 using the expression
Tc = A(H-Hc1)^v. The exponent v = 0.65(2), obtained at temperatures much
smaller than 8 K, is that of the 3D Bose-Einstein condensate (BEC) universality
class. This finding strongly suggests that Sr3Cr2O8 is a new realization of a
triplon BEC where the universal regimes corresponding to both Hc1 and Hc2 are
accessible at He-4 temperatures.Comment: 4 pages, 3 figures, accepted by PR
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