32 research outputs found
Physical properties of misfit-layered (Bi,Pb)-Sr-Co-O system: Effect of hole doping into triangular lattice formed by low-spin Co ions
Pb-doping effect on physical properties of misfit-layered (Bi,Pb)-Sr-Co-O
system, in which Co ions form a two-dimensional triangular lattice, was
investigated in detail by electronic transport, magnetization and specific-heat
measurements. Pb doping enhances the metallic behavior, suggesting that
carriers are doped. Pb doping also enhances the magnetic correlation in this
system and increases the magnetic transition temperature. We found the
existence of the short-range magnetic correlation far above the transition
temperature, which seems to induce the spin-glass state coexisting with the
ferromagnetic long-range order at low temperatures. Specific-heat measurement
suggests that the effective mass of the carrier in (Bi,Pb)-Sr-Co-O is not
enhanced so much as reported in NaCoO. Based on these experimental
results, we propose a two-bands model which consists of narrow and
rather broad bands. The observed magnetic property and
magnetotransport phenomena are explained well by this model
Dual electronic states in thermoelectric cobalt oxide
We investigate the low temperature magnetic field dependence of the
resistivity in the thermoelectric misfit cobalt oxide [Bi1.7Ca2O4]0.59CoO2 from
60 K down to 3 K. The scaling of the negative magnetoresistance demonstrates a
spin dependent transport mechanism due to a strong Hund's coupling. The
inferred microscopic description implies dual electronic states which explain
the coexistence between localized and itinerant electrons both contributing to
the thermopower. By shedding a new light on the electronic states which lead to
a high thermopower, this result likely provides a new potential way to optimize
the thermoelectric properties
Transport properties and magnetic field induced localization in the misfit cobaltite [BiBaKCo][CoO] single crystal
Resistivity under magnetic field, thermopower and Hall coefficient are
systematically studied for
[BiBaKCo][CoO] single crystal.
In-plane resistivity ((T)) shows metallic behavior down to 2 K with
a dependence below 30 K; while out-of-plane resistivity ()
shows metallic behavior at high temperature and a thermal activation
semiconducting behavior below about 12 K. Striking feature is that magnetic
field induces a ln(1/) diverging behavior in both and
at low temperature. The positive magnetoresistance (MR) could be
well fitted by the formula based on multi-band electronic structure. The
ln(1/) diverging behavior in and could arise from
the magnetic-field-induced 2D weak localization or spin density wave.Comment: 7 pages, 8 figure
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
Novel electronic structure induced by a highly strained oxide interface with incommensurate crystal fields
The misfit oxide, BiBaKCoO, made of
alternating rocksalt-structured [BiO/BaO] layers and hexagonal CoO
layers, was studied by angle-resolved photoemission spectroscopy. Detailed
electronic structure of such a highly strained oxide interfaces is revealed for
the first time. We found that under the two incommensurate crystal fields,
electrons are confined within individual sides of the interface, and scattered
by umklapp scattering of the crystal field from the other side. In addition,
the high strain on the rocksalt layer raises its chemical potential and induces
large charge transfer to the CoO layer. Furthermore, a novel interface
effects, the interfacial enhancement of electron-phonon interactions, is
discovered. Our findings of these electronic properties lay a foundation for
designing future functional oxide interfaces.Comment: 5 pages, 4 figure
Structural investigation of composite phases Ba1+x[(NaxMn1-x)O-3] with x similar or equal to 2/7, 5/17 and 1/3; exotic Mn4.5+ valence
International audienceStructural models are proposed for three composite compounds of chemical formula Ba1+x[(NaxMn1-x)O-3] (x similar or equal to 2/7, 5/17 and 1/3) by single crystal X-ray diffraction; superspace formalism is used to obtain an unified description of the three phases. The modulation affecting Ba atoms can be easily designed but the competition "occupational/displacive" modulations relating to the Mn/Na metallic columns were particularly difficult to modelize. However, the large amplitude of the displacive modulation affecting the oxygen atoms (similar or equal to +/- 0.7 angstrom) in comparison with that observed for related compounds (similar or equal to +/- 0.3 angstrom) makes it a direct consequence of the Na+ alkali insertion inside the trigonal prisms. Owing to this insertion, the Mn atoms exhibit, in the three phases, an "exotic" oxidation state of about +4.5. In addition, even if the sequence between face sharing MnO6 octahedra and NaO6 trigonal prisms can be analytically deduced from the x value, it is clear that the Na/Mn contrasts play in favour of its accurate determination through the XRD single crystal refinement
Structural Study of P4W14O50, a New Odd Member in the Series (PO2)4(WO3)2m
International audienc