On the origin of magnetoresistance in Sr${}_2$FeMoO${}_6$

We report detailed magnetization ($M$) and magnetoresistance ($MR$) studies on a series of Sr${}_2$FeMoO${}_6$ samples with independent control on anti-site defect and grain boundary densities. These results, exhibiting a switching-like behavior of $MR$ with $M$, establish that the $MR$ is controlled by the magnetic polarization of grain boundary regions, rather than of the grains within a resonant tunnelling mechanism.