5 research outputs found
Prediction of Orbital Ordering in Single-Layered Ruthenates
The key role of the orbital degree of freedom to understand the magnetic
properties of layered ruthenates is here discussed. In the G-type
antiferromagnetic phase of CaRuO, recent X-ray experiments reported the
presence of 0.5 hole per site in the orbital, while the
and orbitals contain 1.5 holes. This unexpected hole
distribution is explained by a novel state with orbital ordering (OO),
stabilized by a combination of Coulomb interactions and lattice distortions. In
addition, the rich phase diagram presented here suggests the possibility of
large magnetoresistance effects, and predicts a new ferromagnetic OO phase in
ruthenates.Comment: 4 pages, Revtex, with 2 figures embedded in the text. Submitted to
Phys. Rev. Let
Competition between ferromagnetic and charge-orbital ordered phases in PrCaMnO for =1/4, 3/8, and 1/2
Spin, charge, and orbital structures in models for doped manganites are
studied by a combination of analytic mean-field and numerical relaxation
techniques. At realistic values for the electron-phonon and antiferromagnetic
spin couplings, a competition between a ferromagnetic (FM) phase and a
charge-orbital ordered (COO) insulating state is found for =1/4, 3/8, and
1/2, as experimentally observed in PrCaMnO for
=0.30.5. The theoretical predictions for the spin-charge-orbital
ordering pattern are compared with experiments. The FM-COO energy difference is
surprisingly small for the densities studied, result compatible with the
presence of a robust colossal-magnetoresistive effect in
PrCaMnO in a large density interval.Comment: 4 pages, Revtex, with 2 figures embedded in the text. Submitted to
Phys. Rev.
A-type Antiferromagnetic and C-type Orbital-Ordered State in LaMnO Using Cooperative Jahn-Teller Phonons
The effect of Jahn-Teller phonons on the magnetic and orbital structure of
LaMnO is investigated using a combination of relaxation and Monte Carlo
techniques on three-dimensional clusters of MnO octahedra. In the
physically relevant region of parameter space for LaMnO, and after
including small corrections due to tilting effects, the A-type
antiferromagnetic and C-type orbital structures were stabilized, in agreement
with experiments.Comment: 4 pages, Revtex, with 3 figures embedded in the text. Submitted to
Phys. Rev.