748 research outputs found
Tuning the spin dynamics of kagome systems
Despite the conceptional importance of realizing spin liquids in solid states
only few compounds are known. On the other side the effect of lattice
distortions and anisotropies on the magnetic exchange topology and the
fluctuation spectrum are an interesting problem. We compare the excitation
spectra of the two s=1/2 kagome lattice compounds volborthite and vesignieite
using Raman scattering. We demonstrate that even small modifications of the
crystal structure may have a huge effect on the phonon spectrum and low
temperature properties.Comment: 3 pages, 2 figure
Heterogeneous spin state in the field-induced phase of volborthite as seen via 51V nuclear magnetic resonance
We report results of 51V NMR in the field-induced phase of volborthite
Cu3V2O7(OH)dot2H2O, a spin-1/2 antiferromagnet on a distorted kagome lattice.
In magnetic fields above 4.5 T, two types of V sites with different spin-echo
decay rates are observed. The hyperfine field at the fast decaying sites has a
distribution, while it is more homogeneous at the slowly decaying sites. Our
results indicate a heterogeneous state consisting of two spatially alternating
Cu spin systems, one of which exhibits anomalous spin fluctuations contrasting
with the other showing a conventional static order.Comment: 5 pages, 4 figure
Phase Diagram and Spin Dynamics in Volborthite with a Distorted Kagome Lattice
We report 51V-NMR study on a high-quality powder sample of volborthite
Cu3V2O7(OH)2/2H2O, a spin-1/2 Heisenberg antiferromagnet on a distorted kagome
lattice formed by isosceles triangles. In the magnetic fields below 4.5 T, a
sharp peak in the nuclear spin-lattice relaxation rate 1/T1 accompanied with
line broadening revealed a magnetic transition near 1 K. The low temperature
phase shows anomalies such as a Lorentzian line shape, a 1/T1 propto T behavior
indicating dense low energy excitations, and a large spin-echo decay rate 1/T2
pointing to unusually slow fluctuations. Another magnetic phase appears above
4.5 T with less anomalous spectral shape and dynamics.Comment: 4 pages, 4 figure
Spin-1/2 kagome compounds: volborthite vs herbertsmithite
Two kagome compounds, volborthite Cu3V2O7(OH)2-2H2O and herbertsmithite
ZnCu3(OH)6Cl2, are compared in order to derive information about the intrinsic
properties of the spin-1/2 kagome antiferromagnet. Volborthite shows a broad
maximum at T ~ J / 4 and the approach at T = 0 to a large finite value of the
bulk magnetic susceptibility chi_bulk as well as the local susceptibility
chi_local from NMR measurements. These must be intrinsic properties for the
spin-1/2 kagome antiferromagnet, as similar behavior has also been reported in
chi_local for herbertsmithite [Olariu A et al. 2008 Phys. Rev. Lett., 100
087202]. Impurity effects that may significantly influence the bulk properties
are discussed.Comment: 8 pages, to be published in J. Phys.: Conf. Series; Proc. of HFM200
Magnetization Process of Kagome-Lattice Heisenberg Antiferromagnet
The magnetization process of the isotropic Heisenberg antiferromagnet on the
kagome lattice is studied. Data obtained from the numerical-diagonalization
method are reexamined from the viewpoint of the derivative of the magnetization
with respect to the magnetic field. We find that the behavior of the derivative
at approximately one-third of the height of the magnetization saturation is
markedly different from that for the cases of typical magnetization plateaux.
The magnetization process of the kagome-lattice antiferromagnet reveals a new
phenomenon, which we call the "magnetization ramp".Comment: 4 pages, 5figures, accepted in J. Phys. Soc. Jpn
High-field Phase Diagram and Spin Structure of Volborthite Cu3V2O7(OH)2/2H2O
We report results of 51V NMR experiments on a high-quality powder sample of
volborthite Cu3V2O7(OH)2/2H2O, a spin-1/2 Heisenberg antiferromagnet on a
distorted kagome lattice. Following the previous experiments in magnetic fields
below 12 T, the NMR measurements have been extended to higher fields up to
31 T. In addition to the two already known ordered phases (phases I and II), we
found a new high-field phase (phase III) above 25 T, at which a second
magnetization step has been observed. The transition from the paramagnetic
phase to the antiferromagnetic phase III occurs at 26 K, which is much higher
than the transition temperatures from the paramagnetic to the lower field
phases I (B < 4.5 T) and II (4.5 < B < 25 T). At low temperatures, two types of
the V sites are observed with different relaxation rates and line shapes in
phase III as well as in phase II. Our results indicate that both phases II and
III exhibit a heterogeneous spin state consisting of two spatially alternating
Cu spin systems, one of which exhibits anomalous spin fluctuations contrasting
with the other showing a conventional static order. The magnetization of the
latter system exhibits a sudden increase upon entering into phase III,
resulting in the second magnetization step at 26 T.We discuss the possible spin
structure in phase III.Comment: 9 pages, 12 figure
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