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Abstract:
First-principles electronic structure calculations have been carried out
on ordered double perovskites Sr(2)B(')B(')O(6) (for B(')=Cr or Fe and
B(') 4d and 5d transition-metal elements) with increasing number of
valence electrons at the B(') sites and on Ba(2)MnReO(6) as well as
Ba(2)FeMoO(6). The Curie temperatures are estimated ab initio from the
electronic structures obtained with the local spin-density functional
approximation, full-potential generalized gradient approximation and/or
the LDA+U method (LDA, local density approximation; U, Hubbard
parameter). Frozen spin spirals are used to model the excited states
needed to evaluate the spherical approximation for the Curie
temperatures. In cases where the induced moments on the oxygen were
found to be large, the determination of the Curie temperature is
improved by additional exchange functions between the oxygen atoms and
between oxygen and B(') and B(') atoms. Pronounced systematics can be
found among the experimental and/or calculated Curie temperatures and
the total valence electrons of the transition-metal elements.
