Structural phase transition and magnetic properties of the Sr2FeRe1-xBx′O6 (B′ = Nb, Ta; x=0, 0.1) double perovskites

The double perovskites, Sr2FeReO6 and Sr2FeRe0.9M0.1O6 (M=Nb, Ta) have been obtained by soft synthesis methods which yield homogeneous particles of micrometric grain size. The materials have been studied by X-ray and neutron powder diffraction, scanning electron microscopy and magnetic measurements. Rietveld refinements show that the compounds adopt a tetragonal 14/mmm structure at high temperatures and monoclinic P2(1)/n below the transition temperature. The magnetic structures were determined by neutron powder diffraction at 100 and 300 K for the Sr2FeReO6, Sr2FeRe0.9Nb0.1O6 and Sr2FeRe0.9Ta0.1O6 phases, respectively. Evidence for a ferrimagnetic coupling between the Fe3+ and Re5+ sublattices has been observed. Magnetic measurements yield magnetic moments lower than the theoretical ones being in accord with the antisite disorder of 25% in the B-B' positions. (C) 2004 Elsevier Inc. All rights reserved.