Crystal structure and magnetism of the double perovskites A₂FeReO₆ (A = Ca, Sr, Ba)

We synthesized a series of double perovskites A(2)FeReO(6) (A = Ca, Sr, Ba) with Curie temperatures above room-temperature. Neutron and X-ray diffraction analysis have been performed in order to determine the structural and (local) magnetic properties of these materials. While Ba2FeReO6 stays cubic over the whole temperature range we examined, the Sr-compound shows a tetragonal distortion of the perovskite structure which does not completely vanish up to about 520 K far above T-C. Ca2FeReO6 has a monoclinic unit cell at high temperatures. Below 400 K a phase separation in two monoclinic phases with identical cell volume is observed in neutron scattering. (C) 2004 Elsevier B.V. All rights reserved