Spin polarization in ordered and disordered double-perovskites

Recently, the double perovskites family A2MM'O6 (A being a divalent or trivalent cation and M, M' two transition metals) has attracted considerable interest with the view of using these materials in spin electronics. This has been triggered but the fact that some members, in particular SrFe2MoO6, present a Curie temperature TC above room temperature and complete spin polarization. In view of improving the performances of these materials, it is therefore fundamental to understand the role of electronic and structural parameters controlling the half-metallic character together with a Curie temperature as high as possible. Fe-Mo double perovskites usually present some degree of Fe/Mo disorder which generally increases with the doping. We present a model considering a correlated electron picture with localized Fe-spins and conduction electron originating from the metals M and M' interacting with the local spins via a double-exchange type mechanism. This succeeds in stabilizing a ferromagnetic ground state in the absence of disorder. We will examine how electron disorder affect the ground state properties with a particular emphasis on the spin polarization.