Comment on the magnetic properties of the system Sr2-xCaxFeMoO6, 0≤x≤2

The structural and magnetic properties of the n-type-metallic double-perovskite system Sr2-xCaxFeMoO6 are reported. At 5 K, the saturation magnetization remains M-s(5 K)=3.5 mu(B)/formula unit compared to a theoretical spin-only moment of 4.0 mu(B)/formula unit for a perfectly ordered compound. From the shape of the M-H hysteresis loops below T-c, it is suggested that ferromagnetic long-range ordered domains are coupled antiferromagnetically across antiphase boundaries; random disorder within domains may be small. An unprecedented dependence of the paramagnetic susceptibility on the applied magnetic field is reported and attributed to an overlapping Fe3+/Fe2+ and Mo6+/Mo5+ redox couple, first suggested by Sleight and Weiher [Sleight AW,Weiher JF. J. Phys Chem Solids 1972; 33. 679.], which results in localized S=5/2 spins on the iron atoms coexisting with itinerant minority-spin electrons in a narrow pi* band. (C) 2000 Published by Elsevier Science Ltd. Ail rights reserved.