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Electronic structures of double perovskites
Sr2(Mn1−xFex)MoO6 (x = 0.0, 0.5, 1.0) have been
studied by using the LSDA +U method, where the on-site Coulomb interaction
U of
localized d electrons has been considered in the local-spin density approximation. The band structure
of Sr2MnMoO6 with antiferromagnetic structure is found to be semiconducting with a gap of 0.5 eV, which is
in good agreement with recent optical absorption results. The optical absorption corresponding
to this optical threshold is found to be a non-vertical transition, which can occur only if a
non-zero momentum such as from phonons participates in the transition. With the increase of
x, the band becomes half-metallic and ferrimagnetic. These semiconductor–metal and
magnetic structure transitions can be rationalized by different characteristics of charge
transfers between Fe–Mo and Mn–Mo via intermediate O 2p orbitals. The down-spin Mo
t2g states cross the
Fermi energy (EF) in the presence of Fe ions. With the increase of
x, more states
cross over EF, which explains the high conductivity in the compound with large
x observed in experiment.
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