Structural and magnetic properties of (Sr2-xCax)FeReO6

The compounds (Sr2-xCax)FeReO6 (x=0, 0.2, 0.5, 1.0, 1.5, and 2.0) were synthesized by solid state reaction. The resistivity exhibits a metallic behavior for Sr2FeReO6 and insulating behavior for Ca2FeReO6. Structural transformation is observed from tetragonal (xless than or equal to1) to monoclinic (xgreater than or equal to1.5). The Curie temperature increases from 405 K for x=0 to 539 K for x=2. The saturation magnetic moment is always less than the 3 mu(B) anticipated for a ferrimagnetic configuration of Fe3+ and Re5+, suggesting some antisite disorder. All compounds exhibit significant coercivity, which increases with increasing Ca content, from 0.2 T for x=0 to 1.1 T for x=2. The unexpectedly large coercivity in these compounds is attributed to intrinsic magnetic anisotropy of the Re5+ ions. Mossbauer spectra indicate a small admixture of 0.2-0.3 electrons in 3d(down arrow)(Fe)t(2g) orbitals. (C) 2002 American Institute of Physics.