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

The structural and magnetic properties of the n-type-metallic double-perovs kite system Sr2-xCaxFeMoO6 are reported. At 5 K, the saturation magnetizati on remains M-s(5 K)=3.5 mu(B)/formula unit compared to a theoretical spin-o nly 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 ferr omagnetic long-range ordered domains are coupled antiferromagnetically acro ss antiphase boundaries; random disorder within domains may be small. An un precedented dependence of the paramagnetic susceptibility on the applied ma gnetic field is reported and attributed to an overlapping Fe3+/Fe2+ and Mo6 +/Mo5+ redox couple, first suggested by Sleight and Weiher [Sleight AW,Weih er 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 righ ts reserved.