Structural and magnetic properties of (Sr <inf>2-x</inf>Ca <inf>x</inf>) FeReO <inf>6</inf>

The compounds (Sr 2-xCa x)FeReO 6 (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 Sr 2FeReO 6 and insulating behavior for Ca 2FeReO 6. Structural transformation is observed from tetragonal (x≤1) to monoclinic (x≥1.5). 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 μ B anticipated for a ferrimagnetic configuration of Fe 3+ and Re 5+, 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 Re 5+ ions. Mössbauer spectra indicate a small admixture of 0.2-0.3 electrons in 3d ↓(Fe)t 2g orbitals. © 2002 American Institute of Physics.