1,930 research outputs found
Magnetic and Transport Properties in (=00.4)
Magnetic and transport properties of () system have been investigated. A broad maximum in M(T) curve,
indicative of low-dimensional antiferromagnetic ordering originated from
layers, is observed in Ca-free sample. With increasing Ca
doping level up to 0.2, the M(T) curve remains almost unchanged, while
resistivity is reduced by three orders. Higher Ca doping level leads to a
drastic change of magnetic properties. In comparison with the samples with
, the temperature corresponding to the maximum of M(T) is much
lowered for the sample =0.3. The sample =0.4 shows a small kink instead
of a broad maximum and a weak ferromagnetic feature. The electrical transport
behavior is found to be closely related to magnetic properties for the sample
=0.2, 0.25, 0.3, 0.4. It suggests that layers are involved
in charge transport in addition to conducting planes to interpret the
correlation between magnetism and charge transport. X-ray photoelectron
spectroscopy studies give an additional evidence of the the transfer of the
holes into the charge reservoir
Nanoarchitectured 3D cathodes for Li-Ion microbatteries
Microbatteries with large area capacity and no power limitation can be obtained by designing 3D structured batteries. 3D electrodes composed of 30 nm-thick films of LiCoO2 coating free-standing columns of Al current collector were achieved. By comparison with a planar electrode presenting an equivalent nominal capacity, a 3D electrode exhibits improved capacity retention: 68% of the nominal capacity at 8C instead of 11%
Two-stage spin-flop transitions in S = 1/2 antiferromagnetic spin chain BaCu_2Si_2O_7
Two-stage spin-flop transitions are observed the in quasi-one-dimensional
antiferromagnet, BaCuSiO. A magnetic field applied along the
easy axis induces a spin-flop transition at 2.0 T followed by a second
transition at 4.9 T. The magnetic susceptibility indicates the presence of
Dzyaloshinskii-Moriya (DM) antisymmetric interactions between the intrachain
neighboring spins. We discuss a possible mechanism whereby the geometrical
competition between DM and interchain interactions, as discussed for the
two-dimensional antiferromagnet LaCuO, causes the two-stage
spin-flop transitions.Comment: 5 pages, 3 figures (included), accepted for publication in Phys. Rev.
Let
Ferromagnetism and large negative magnetoresistance in Pb doped Bi-Sr-Co-O misfit-layer compound
Ferromagnetism and accompanying large negative magnetoresistance in
Pb-substituted Bi-Sr-Co-O misfit-layer compound are investigated in detail.
Recent structural analysis of (Bi,Pb)SrCoO, which has
been believed to be a Co analogue of
BiSrCaCuO, revealed that it has a more complex
structure including a CoO hexagonal layer [T. Yamamoto {\it et al.}, Jpn.
J. Appl. Phys. {\bf 39} (2000) L747]. Pb substitution for Bi not only
introduces holes into the conducting CoO layers but also creates a
certain amount of localized spins. Ferromagnetic transition appears at =
3.2 K with small spontaneous magnetization along the axis, and around the
transition temperature large and anisotropic negative magnetoresistance was
observed. This compound is the first example which shows ferromagnetic
long-range order in a two-dimensional metallic hexagnonal CoO layer.Comment: 8 pages including eps figures. To be published in J. Phys. Soc. Jp
Phase Decomposition and Chemical Inhomogeneity in Nd2-xCexCuO4
Extensive X-ray and neutron scattering experiments and additional
transmission electron microscopy results reveal the partial decomposition of
Nd2-xCexCuO4 (NCCO) in a low-oxygen-fugacity environment such as that typically
realized during the annealing process required to create a superconducting
state. Unlike a typical situation in which a disordered secondary phase results
in diffuse powder scattering, a serendipitous match between the in-plane
lattice constant of NCCO and the lattice constant of one of the decomposition
products, (Nd,Ce)2O3, causes the secondary phase to form an oriented,
quasi-two-dimensional epitaxial structure. Consequently, diffraction peaks from
the secondary phase appear at rational positions (H,K,0) in the reciprocal
space of NCCO. Additionally, because of neodymium paramagnetism, the
application of a magnetic field increases the low-temperature intensity
observed at these positions via neutron scattering. Such effects may mimic the
formation of a structural superlattice or the strengthening of
antiferromagnetic order of NCCO, but the intrinsic mechanism may be identified
through careful and systematic experimentation. For typical reduction
conditions, the (Nd,Ce)2O3 volume fraction is ~1%, and the secondary-phase
layers exhibit long-range order parallel to the NCCO CuO2 sheets and are 50-100
angstromsthick. The presence of the secondary phase should also be taken into
account in the analysis of other experiments on NCCO, such as transport
measurements.Comment: 15 pages, 17 figures, submitted to Phys. Rev.
New superconduting cuprates with no effective doping: T'-(La3+)2-x(RE3+)xCuO4
We report the synthesis of new superconducting cuprates T'-La2-xRExCuO4 (RE =
Sm, Eu, Tb, Lu, and Y) using molecular beam epitaxy. The new superconductors
have no effective dopant, at least nominally. The substitution of isovalent RE
for La was essentially performed to stabilize the T' phase of La2CuO4 instead
of the T phase. The maximum Tconset is ~ 25 K and Tczero is ~ 21 K. The keys to
our discovery are (1) the preparation of high-crystalline-quality La-based T'
films by low-temperature (~ 650C) thin film processes, and (2) more thorough
removal of impurity oxygen at the apical site, which is achieved by the larger
in-plane lattice constant (a0) of T'-La2-xRExCuO4 than other T'-Ln2CuO4 (Ln =
Pr, Nd, Sm, Eu, Gd) with the aid of large surface-to-volume ratio of thin
films.Comment: 10 pages, 5 figures (Proceedings of the 16th international symposium
on superconductivity (ISS 2003), to be published in Physica C
Doubling of the bands in overdoped Bi2Sr2CaCu2O8-probable evidence for c-axis bilayer coupling
We present high resolution ARPES data of the bilayer superconductor
Bi2Sr2CaCu2O8 (Bi2212) showing a clear doubling of the near EF bands. This
splitting approaches zero along the (0,0)-(pi,pi) nodal line and is not
observed in single layer Bi2Sr2CuO6 (Bi2201), suggesting that the splitting is
due to the long sought after bilayer splitting effect. The splitting has a
magnitude of approximately 75 meV near the middle of the zone, extrapolating to
about 100 meV near the (pi,0) poin
Magnetic ordering in Sr2RuO4 induced by nonmagnetic impurities
We report unusual effects of nonmagnetic impurities on the spin-triplet
superconductor Sr2RuO4. The substitution of nonmagnetic Ti4+ for Ru4+ induces
localized-moment magnetism characterized by unexpected Ising anisotropy with
the easy axis along the interlayer c direction. Furthermore, for x(Ti) > 0.03
magnetic ordering occurs in the metallic state with the remnant magnetization
along the c-axis. We argue that the localized moments are induced in the Ru4+
and/or oxygen ions surrounding Ti4+ and that the ordering is due to their
interaction mediated by itinerant Ru-4d electrons with strong spin
fluctuations.Comment: 5 pages, 4figure
Large, high quality single-crystals of the new Topological Kondo Insulator, SmB6
SmB6 has recently been predicted to be a Topological Kondo Insulator, the first strongly correlated heavy fermion material to exhibit topological surface states. High quality crystals are necessary to investigate the topological properties of this material. Single crystal growth of the rare earth hexaboride, SmB6, has been carried out by the floating zone technique using a high power xenon arc lamp image furnace. Large, high quality single-crystals are obtained by this technique. The crystals produced by the floating zone technique are free of contamination from flux materials and have been characterised by resistivity and magnetisation measurements. These crystals are ideally suited for the investigation of both the surface and bulk properties of SmB6
INTERLAYER COUPLING AND THE METAL-INSULATOR TRANSITION IN Pr-SUBSTITUTED Bi(2)Sr(2)CaCu(2)O(8+y)
Substitution of rare-earth ions for Ca in Bi2Sr2CaCu2O8+y is known to cause a
metal-insulator transition. Using resonant photoemission we study how this
chemical substitution affects the electronic structure of the material. For the
partial Cu-density of states at E_F and in the region of the valence band we
observe no significant difference between a pure superconducting sample and an
insulating sample with 60% Pr for Ca. This suggests that the states responsible
for superconductivity are predomi- nately O-states. The partial Pr-4f density
of states was extracted utilizing the Super- Koster-Kronig Pr 4d-4f resonance.
It consists of a single peak at 1.36eV binding energy. The peak shows a
strongly assymetric Doniach-Sunjic line- shape indicating the presence of a
continuum of electronic states with sharp cut off at E_F even in this
insulating sample. This finding excludes a bandgap in the insulating sample and
supports the existance of a mobility gap caused by spatial localization of the
carriers. The presence of such carriers at the Pr-site, between the CuO_2
planes shows that the electronic structure is not purely 2-dimensional but that
there is a finite interlayer coupling. The resonance enhancement of the
photoemission cross section, at the Pr-4d threshold, was studied for the Pr-4f
and for Cu-states. Both the Pr-4f and the Cu-states show a Fano-like resonance.
This resonance of Cu-states with Pr-states is another indication of coupling
between the the Pr-states and those in the CuO_2 plane. Because of the
statistical distribution of the Pr-ions this coupling leads to a non-periodic
potential for the states in the CuO_2 plane which can lead to localization and
thus to the observed metal-insulator transition.Comment: Gziped uuencoded postscript file including 7 figures Scheduled for
publication in Physical Review B, May 1, 1995
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