The effect of isoelectronic substitution on the magneto-resistance of Sr2−xBaxFeMoO6

We report results from structural, transport and magnetic measurements on polycrystalline Sr_2−xBa_xFeMoO₆ (x=0, 1 and 2) half-metallic double perovskites. We find a large low field magneto-resistance (MR) of −25% at 0.8 T and 77 K for samples that have high resistivities. We show that the low field tunneling MR can be modeled by assuming that there is a disordered region near the insulating grain boundaries as proposed by Serrate et al. It is the magnetization from this region rather than the bulk magnetization that determines the MR in polycrystalline samples.