297 research outputs found
Magnetic-Field Induced Gap in One-Dimensional Antiferromagnet KCuGaF
Magnetic susceptibility and specific heat measurements in magnetic fields
were performed on an one-dimensional antiferromagnet KCuGaF.
Exchange interaction was evaluated as K. However, no
magnetic ordering was observed down to 0.46 K. It was found that an applied
magnetic field induces a staggered magnetic susceptibility obeying the Curie
law and an excitation gap, both of which should be attributed to the
antisymmetric interaction of the Dzyaloshinsky-Moriya type and/or the staggered
-tensor. With increasing magnetic field , the gap increases almost in
proportion to .Comment: Submitted to Proceedings of Research in High Magnetic Fiel
Unusual magnetic-field dependence of partially frustrated triangular ordering in manganese tricyanomethanide
Manganese tricyanomethanide, Mn[C(CN)3]2, consists of two interpenetrating
three-dimensional rutile-like networks. In each network, the tridentate C(CN)3-
anion gives rise to superexchange interactions between the Mn2+ ions (S=5/2)
that can be mapped onto the "row model" for partially frustrated triangular
magnets. We present heat capacity measurements that reveal a phase transition
at T_N = 1.18K, indicative of magnetic ordering. The zero-field magnetically
ordered structure was solved from neutron powder diffraction data taken between
0.04 and 1.2 K. It consists of an incommensurate spiral with a temperature
independent propagation vector Q=(2Q 0 0)=(+/-0.622 0 0), where different signs
relate to the two different networks. This corresponds to (+/-0.311 +/-0.311 0)
in a quasi-hexagonal representation. The ordered moment mu=3.3mu_B is about 2/3
of the full Mn2+ moment. From the values of T_N and Q, the exchange parameters
J/k = 0.15 K and J'/J = 0.749 are estimated. The magnetic-field dependence of
the intensity of the Bragg reflection, measured for external fields
H||Q, indicates the presence of three different magnetic phases. We associate
them with the incommensurate spiral (H < 13.5 kOe), an intermediate phase (13.5
kOe 16 kOe)
proposed for related compounds. For increasing fields, Q continuously
approaches the value 1/3, corresponding to the commensurate magnetic structure
of the fully frustrated triangular lattice. This value is reached at H_c = 19
kOe. At this point, the field-dependence reverses and Q adopts a value of 0.327
at 26 kOe, the highest field applied in the experiment. Except for H_c, the
magnetic ordering is incommensurate in all three magnetic phases of
Mn[C(CN)3]2.Comment: accepted for publication in J. Phys.: Condens. Matte
Electron Spin Resonance in sine-Gordon spin chains in the perturbative spinon regime
We report the low-temperature multi-frequency ESR studies of copper
pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating
-tensor and the Dzyaloshinskii-Moriya interaction, allowing us to test a new
theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett.
82, 5136 (1999)]. Their theory, based on bosonization and the self-energy
formalism, can be applied for precise calculation of ESR parameters of
antiferromagnetic chains in the perturbative spinon regime. Excellent
quantitative agreement between the theoretical predictions and experiment is
obtained.Comment: 4 pages, 4 figure
Rare earth magnetism and ferroelectricity in RMnO3
Magnetic rare earths R have been proven to have a significant effect on the
multiferroic properties of the orthorhombic manganites RMnO3. A re-examination
of previous results from synchrotron based x-ray scattering experiments
suggests that symmetric exchange striction between neighboring R and Mn ions
may account for the enhancement of the ferroelectric polarization in DyMnO3 as
well as the magnetic-field induced ferroelectricity in GdMnO3. In general,
adding a second magnetic species to a multiferroic material may be a route to
enhance its ferroelectric properties.Comment: Contribution to ICM 2009; accepted for publication in Journal of
Physics: Conference Serie
Valence modulations in CeRuSn
CeRuSn exhibits an extraordinary room temperature structure at 300~K with
coexistence of two types of Ce ions, namely trivalent Ce and
intermediate valent Ce, in a metallic environment. The ordered
arrangement of these two Ce types on specific crystallographic sites results in
a doubling of the unit cell along the -axis with respect to the basic
monoclinic CeCoAl-type structure. Below room temperature, structural modulation
transitions with very broad hysteresis have been reported from measurements of
various bulk properties. X-ray diffraction revealed that at low temperatures
the doubling of the CeCoAl type structure is replaced by a different modulated
ground state, approximating a near tripling of the basic CeCoAl cell. The
transition is accompanied by a significant contraction of the axis. We
present new x-ray absorption near-edge spectroscopy data at the Ce L
absorption edge, measured on a freshly cleaved surface of a CeRuSn single
crystal. In contrast to a previous report, the new data exhibit small but
significant variations as function of temperature that are consistent with a
transition of a fraction of Ce ions to the intermediate valence state,
analogous to the transition in elemental cerium,
when cooling through the structural transitions of CeRuSn. Such results in a
valence-modulated state
Field-Induced Gap in a Quantum Spin-1/2 Chain in a Strong Magnetic Field
Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2
antiferromagnetic chain with alternating -tensor and Dzyaloshinskii-Moriya
interactions that exhibits a field-induced spin gap, are probed by means of
pulsed-field electron spin resonance spectroscopy. In particular, we report on
a minimum of the gap in the vicinity of the saturation field T
associated with a transition from the sine-Gordon region (with soliton-breather
elementary excitations) to a spin-polarized state (with magnon excitations).
This interpretation is fully confirmed by the quantitative agreement over the
entire field range of the experimental data with the DMRG investigation of the
spin-1/2 Heisenberg chain with a staggered transverse field
Commensurate Dy magnetic ordering associated with incommensurate lattice distortion in orthorhombic DyMnO3
Synchrotron x-ray diffraction and resonant magnetic scattering experiments on
single crystal DyMnO3 have been carried out between 4 and 40 K. Below TN(Dy) =
5K, the Dy magnetic moments order in a commensurate structure with propagation
vector 0.5 b*. Simultaneous with the Dy magnetic ordering, an incommensurate
lattice modulation with propagation vector 0.905 b* evolves while the original
Mn induced modulation is suppressed and shifts from 0.78 b* to 0.81 b*. This
points to a strong interference of Mn and Dy induced structural distortions in
DyMnO3 besides a magnetic coupling between the Mn and Dy magnetic moments.Comment: submitted to Phys. Rev. B Rapid Communication
Excitation hierarchy of the quantum sine-Gordon spin chain in strong magnetic field
The magnetic excitation spectrum of copper pyrimidine dinitrate, a material
containing S=1/2 antiferromagnetic chains with alternating g-tensor and the
Dzyaloshinskii-Moriya interaction, and exhibiting a field-induced spin gap, is
probed using submillimeter wave electron spin resonance spectroscopy. Ten
excitation modes are resolved in the low-temperature spectrum, and their
frequency-field diagram is systematically studied in magnetic fields up to 25
T. The experimental data are sufficiently detailed to make a very accurate
comparison with predictions based on the quantum sine-Gordon field theory.
Signatures of three breather branches and a soliton, as well as those of
several multi-particle excitation modes are identified.Comment: 4 RevTeX pages, 3 figure
Enhanced ferroelectric polarization by induced Dy spin-order in multiferroic DyMnO3
Neutron powder diffraction and single crystal x-ray resonant magnetic
scattering measurements suggest that Dy plays an active role in enhancing the
ferroelectric polarization in multiferroic DyMnO3 above TNDy = 6.5 K. We
observe the evolution of an incommensurate ordering of Dy moments with the same
periodicity as the Mn spiral ordering. It closely tracks the evolution of the
ferroelectric polarization which reaches a maximum value of 0.2 muC/m^2. Below
TNDy, where Dy spins order commensurately, the polarization decreases to values
similar for those of TbMnO3
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