17 research outputs found
Anisotropic phonon conduction and lattice distortions in CMR-type bilayer manganite (LaPr)SrMnO (z=0,0.2,0.4 and 0.6) single crystals
We have undertaken a systematic study of thermal conductivity as a function
of temperature and magnetic field of single crystals of the compound
(LaPr)SrMnO for (Pr) =0.2,0.4. and
0.6. The lattice distortion due to Pr-substitution and anisotropic thermal
conductivity in bilayer manganites are discussed on the basis of different
relaxation models of local lattice distortions in metal and insulating states
proposed by Maderda et al. The giant magnetothermal effect is scaled as a
function of magnetization and discussed on the basis of a systematic variation
of the occupation of the -electron orbital states due to Pr-substitution.Comment: 7 pages, 6 figures, in press in Phys.Rev.
Magnetic, orbital and charge ordering in the electron-doped manganites
The three dimensional perovskite manganites in the range of hole-doping are studied in detail using a double exchange model with degenerate
orbitals including intra- and inter-orbital correlations and near-neighbour
Coulomb repulsion. We show that such a model captures the observed phase
diagram and orbital-ordering in the intermediate to large band-width regime. It
is argued that the Jahn-Teller effect, considered to be crucial for the region
, does not play a major role in this region, particularly for systems
with moderate to large band-width. The anisotropic hopping across the
degenerate orbitals are crucial in understanding the ground state phases
of this region, an observation emphasized earlier by Brink and Khomskii. Based
on calculations using a realistic limit of finite Hund's coupling, we show that
the inclusion of interactions stabilizes th e C-phase, the antiferromagnetic
metallic A-phase moves closer to while th e ferromagnetic phase shrinks
in agreement with recent observations. The charge ordering close to and
the effect of reduction of band-width are also outlined. The effect of disorder
and the possibility of inhomogeneous mixture of competing states have been
discussed.Comment: 42 pages, 16 figure
Crystal Structure and High-Temperature Thermoelectric Properties of the Mo3−x Ru x Sb7 Compounds
Zintl phases are currently receiving great attention for their thermoelectric potential typified by the discovery of a high ZT value in Yb 14MnSb 11-based compounds. Herein, we report on the crystallographic characterization via neutron and x-ray diffraction experiments, and on the thermoelectric properties measured in the 300 K to 1000 K temperature range, of Mo 3Sb 7 and its isostructural compounds Mo 3-x Ru x Sb 7. Even though Mo 3Sb 7 displays rather high ZT values given its metallic character, the partial substitution of Mo by Ru substantially improves its thermoelectric properties, resulting in a ZT value of ∼0.45 at 1000 K for x = 0.8. © 2009 TMS