25 research outputs found
Double exchange and orbital correlations in electron-doped manganites
A double exchange model for degenerate orbitals with intra- and
inter-orbital interactions has been studied for the electron doped manganites
ABMnO (). We show that such a model reproduces the
observed phase diagram and orbital ordering in the intermediate bandwidth
regime and the Jahn-Teller effect, considered to be crucial for the region
, does not play a major role in this region. Brink and Khomskii have
already pointed this out and stressed the relevance of the anistropic hopping
across the degenerate orbitals in the infinite Hund's coupling limit.
From a more realistic calculation with finite Hund's coupling, we show that
inclusion of interactions stabilizes the C-phase, the antiferromagnetic
metallic A-phase moves closer to while the ferromagnetic phase shrinks.
This is in agreement with the recent observations of Kajimoto et. al. and
Akimoto et. al.Comment: text 9 pages, 5 figure
Antiferromagnetism and Superconductivity in a Model with Extended Pairing Interactions
The competition between antiferromagnetism and the superconducting
state is studied in a model with near and next near neighbour interactions in
the absence of any on-site repulsion. A mean field study shows that it is
possible to have simultaneous occurrence of an antiferromagnetic and a singlet
superconducting state in this model. In addition, such a coexistence
generates a triplet superconducting order parameter with centre of mass
momentum {\it dynamically} having the same orbital symmetry as
the singlet superconductor. Inclusion of next nearest neighbour hopping in the
band stabilises the superconducting state away from half filling, the
topology of the phase diagram, though, remains similar to the near neighbour
model. In view of the very recent observation of a broad region of coexistence
of antiferrmagnetic and unconventional superconducting states in organic
superconductors, the possibility of observation of the triplet state has been
outlined.Comment: 12 pages(tex file), 7 figures (ps files
Effects of Fe substitution on the electronic, transport, and magnetic properties of ZnGaO: A systematic ab-initio study
We present a density functional study of Fe doped into the tetrahedral and
octahedral cation sites of the wide band gap spinel ZnGaO.
We calculate the electronic structure for different substitutions and discuss
the magnetic and transport properties for each case considering different
approximations for the exchange-correlation potential. We show that for certain
doped cases, significant differences in the predicted behavior are obtained
depending on the exchange correlation potential adopted. Possible applications
of the doped systems as magnetic semiconductors are outlined.Comment: 9 pages, 8 figures; to be published in Phys. Rev.
Magnetic and orbital order in overdoped bilayer manganites
The magnetic and orbital orders for the bilayer manganites in the doping
region have been investigated from a model that incorporates the
two orbitals at each Mn site, the inter-orbital Coulomb interaction and
lattice distortions. The usual double exchange operates via the orbitals.
It is shown that such a model reproduces much of the phase diagram recently
obtained for the bilayer systems in this range of doping. The C-type phase with
() spin order seen by Ling et al. appears as a natural consequence
of the layered geometry and is stabilised by the static distortions of the
system. The orbital order is shown to drive the magnetic order while the
anisotropic hopping across the orbitals, layered nature of the underlying
structure and associated static distortions largely determine the orbital
arrangements.Comment: 8 pages, 5 figure