22 research outputs found
Growth of large single crystals of Rare Earth Hexaborides
Single crystal growth of several rare earth hexaborides has been carried out
by the floating zone technique. A high power Xenon arc lamp image furnace was
used for the crystal growth. Large high quality crystals of LaB,
CeB, PrB and NdB, about 1 cc in volume have been obtained.
Crystals of all these compounds have also been grown using enriched B
isotope for use in neutron scattering experiments.Comment: 3 pages, 3 figures, in press (J. Crystal Growth
Microwave properties of Nd_0.5Sr_0.5MnO_3: a key role of the (x^2-y^2)-orbital effects
Transmittance of the colossal magnetoresistive compound Nd_0.5Sr_0.5MnO_3
showing metal-insulator phase transition has been studied by means of the
submm- and mm-wavelength band spectroscopy. An unusually high transparency of
the material provided direct evidence for the significant suppression of the
coherent Drude weight in the ferromagnetic metallic state. Melting of the
A-type antiferromagnetic states has been found to be responsible for a
considerable increase in the microwave transmission, which was observed at the
transition from the insulating to the metallic phase induced by magnetic field
or temperature. This investigation confirmed a dominant role of the
(x^2-y^2)-orbital degree of freedom in the low-energy optical properties of
Nd_0.5Sr_0.5MnO_3 and other doped manganites with planar (x^2-y^2)-orbital
order, as predicted theoretically. The results are discussed in terms of the
orbital-liquid concept.Comment: 8 pages, 3 figure
Observation of transverse field components in the flux lattice in the anisotropic superconductor YBa2Cu3O7-¿.
Influence of nonlocal electrodynamics on the anisotropic vortex pinning in
We have studied the pinning force density Fp of YNi_2B_2C superconductors for
various field orientations. We observe anisotropies both between the c-axis and
the basal plane and within the plane, that cannot be explained by usual mass
anisotropy. For magnetic field , the reorientation structural
transition in the vortex lattice due to nonlocality, which occurs at a field
, manifests itself as a kink in Fp(H). When , Fp is
much larger and has a quite different H dependence, indicating that other
pinning mechanisms are present. In this case the signature of nonlocal effects
is the presence of a fourfold periodicity of Fp within the basal plane.Comment: 4 pages, 3 figure
The puzzle of 90 degree reorientation in the vortex lattice of borocarbide superconductors
We explain 90 degree reorientation in the vortex lattice of borocarbide
superconductors on the basis of a phenomenological extension of the nonlocal
London model that takes full account of the symmetry of the system. We propose
microscopic mechanisms that could generate the correction terms and point out
the important role of the superconducting gap anisotropy.Comment: 4 pages, 2 eps figure
Nonlocal Effects and Shrinkage of the Vortex Core Radius in YNi2B2C Probed by muSR
The magnetic field distribution in the vortex state of YNi2B2C has been
probed by muon spin rotation (muSR). The analysis based on the London model
with nonlocal corrections shows that the vortex lattice has changed from
hexagonal to square with increasing magnetic field H. At low fields the vortex
core radius, rho_v(H), decreases with increasing H much steeper than what is
expected from the sqrt(H) behavior of the Sommerfeld constant gamma(H),
strongly suggesting that the anomaly in gamma(H) primarily arises from the
quasiparticle excitations outside the vortex cores.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Tunneling spectroscopy in the magnetic superconductor TmNi2B2C
We present new measurements about the tunneling conductance in the
borocarbide superconductor TmNiBC. The results show a very good
agreement with weak coupling BCS theory, without any lifetime broadening
parameter, over the whole sample surface. We detect no particular change of the
tunneling spectroscopy below 1.5K, when both the antiferromagnetic (AF) phase
and the superconducting order coexist.Comment: Submitted to Phys. Rev. B, Rapid Communication
Comment on Nature of the conduction-band states in YBa2Cu3O7 as revealed by its yttrium Knight shift
A Comment on the Letter by F. J. Adrian, Phys. Rev. Lett. 61, 2148 (1988). © 1989 The American Physical Society
NMR evidence for fluctuating, localised magnetic fields in zinc-doped YBa2Cu3O7-δ
High resolution NMR data for the changes in the shift and relaxation time of the 89Y resonance are presented for a range of zinc and gallium replacements for copper in YBa2Cu3O7-δ. Strikingly different variations in these NMR parameters are detected for the two substitutions. The interpretation of the experimental data leads to the conclusion that the incorporation of non-magnetic zinc impurities in the Cu(II)-O plane produces fluctuating, localised magnetic moments which may be the origin of the destruction of the superconducting state. © 1989
Magnetic properties of a LuVO3 single crystal studied by magnetometry, heat capacity and neutron diffraction
We have studied the magnetic properties of a LuVO3 single crystal. The compound shows an orbital ordering at TOO = 179 K followed by the antiferromagnetic spin ordering at TSO = 109 K. In the magnetically ordered regime, there appears an abrupt change at To = 82.5 K in the magnetisation, indicating a first-order transition. The compound has very large negative Weiss temperature observed along all the main crystallographic axes, suggesting a strong antiferromagnetic correlations in the paramagnetic state. The observation of hysteresis curves in the collinear antiferromagnetic regime is discussed in terms of an inhomogeneity generating some spins with weak local fields in a strongly antiferromagnetic matrix