2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/22593We 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.4 pages, 4 figuresStrongly Correlated ElectronsMaterials Sciencetext