ON THE COMPETITION BETWEEN FERROMAGNETIC AND ANTIFERROMAGNETIC STATES IN Sr2MnMoO6

Recently, the ordered double perovskites Sr2MM O6 (M being the magnetic 3d element, and M ′ being the 4d or 5d element) have attracted a great deal of attention. The interest to these systems was spurred on by large intergrain-tunneling magnetoresistance observed at room temperature in Sr2FeMoO6 and Sr2FeReO6 [1], which opens wide perspectives for technological applications. On the contrary, Sr2MnMoO6 remains paramagnetic down to the very low temperature [2]. The magnetic susceptibility of Sr2MnMoO6 obeys the Curie-Weiss law with fairly large effective moment. However, there is something that prevents formation of the long-range magnetic order in this material (a similar situation occurs in double-layer manganites La2−2xSr1+2xMn2O7 around x=0.7 [3]). In this work we argue that such a behavior may be due to the competition between ferromagnetic (FM) and type-II antiferromagnetic (AFM) phases.