Structural and doping effects in the half-metallic double perovskite A2CrWO6 (A = Sr, Ba, and Ca) -: art. no. 144431

The structural, transport, magnetic, and optical properties of the double perovskite A(2)CrWO(6) with A=Sr,Ba,Ca have been studied. By varying the alkaline earth ion on the A site, the influence of steric effects on the Curie temperature T-C and the saturation magnetization has been determined. A maximum T-C=458 K was found for Sr2CrWO6 having an almost undistorted perovskite structure with a tolerance factor fsimilar or equal to1. For Ca2CrWO6 and Ba2CrWO6 structural changes result in a strong reduction of T-C. Our study strongly suggests that for the double perovskites in general an optimum T-C is achieved only for fsimilar or equal to1, that is, for an undistorted perovskite structure. Electron doping in Sr2CrWO6 by a partial substitution of Sr2+ by La3+ was found to reduce both T-C and the saturation magnetization M-s. The reduction of M-s could be attributed both to band structure effects and the Cr/W antisites induced by doping. Band structure calculations for Sr2CrWO6 predict an energy gap in the spin-up band, but a finite density of states for the spin-down band. The predictions of the band structure calculation are consistent with our optical measurements. Our experimental results support the presence of a kinetic energy driven mechanism in A(2)CrWO(6), where ferromagnetism is stabilized by a hybridization of states of the nonmagnetic W site positioned in between the high spin Cr sites.