Microscopic model, spin wave theory, and competing orders in
double perovskites
George Jackeli
Institute for Theoretical Physics, Ecole Polytechnique Federale de Lausanne, CH-1015, Lausanne, Switzerland
We present a microscopic theory of carrier-induced ferrimagnetism in metallic
double perovskite compounds such as
Sr2 FeMoO6 and Sr2 FeReO6
which have recently attracted intense interest for their possible applications
to magnetotransport devices.
The theory is based on an effective "Kondo-like" Hamiltonian treated here
within the large-S expansion.
We find that depending on the value of the carrier density
the ground state is either a ferrimagnet or a layered antiferromagnet.
The ferrimagnetic state has a robust half-metallic electronic structure.
The transition to antiferromagnetic phase is first order accompanied
with the regime
of phase separation.
We study spin wave spectrum including quantum corrections
and find strongly enhanced quantum effects in the vicinity of zero-temperature
phase transition.
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