Simultaneous Jahn-Teller distortion and magnetic order in the double perovskite Ba2154SmMoO6

An unexpectedly high antiferromagnetic transition temperature (T(N)=130 K) has been observed in the double perovskite Ba(2)(154)SmMoO(6) as a result of a strong interplay between spin, orbital, and lattice degrees of freedom. The crystal structure distorts from tetragonal (space group I4/m) to triclinic (space group I-1) as the temperature is reduced below 353 K. A Jahn-Teller distortion is observed at T(N) so that a tetragonal elongation of the MoO(6) octahedra is observed. It is suggested that orbital order precipitates antiferromagnetic order with anomalously high T(N) in the 4d(1) Mo(5+) Ba(2)REMoO(6) (RE=Sm, Eu) double perovskites.