Grain-boundary room-temperature low-field magnetoresistance in Sr2FeMoO6 films

Thin films of (001)-oriented ${\mathrm{Sr}}_{\mathrm{2}}{\mathrm{FeMoO}}_6$ have been epitaxially deposited or ${\mathrm{LaAlO}}_3$ and ${\mathrm{SrTiO}}_3$ (001) substrates by pulsed laser deposition. The deposition conditions were optimized. Single-phase ${\mathrm{Sr}}_{\mathrm{2}}{\mathrm{FeMoO}}_6$ was obtained in 100 mTorr 99.999% Ar gas at 825 °C. Transport and magnetic data showed a metallic temperature dependence and a saturation magnetization $M_s$ at 10 K of ${\text{3.2μ}}_B/\mathrm{f.u.}$ However, the Curie temperature $T_{\mathrm{C}}\mathrm{\approx 380 K}$ was reduced from 415 K found for tetragonal polycrystalline best ceramics, which lowers $M_s$ at 300 K in the thin films to ${\text{1.5μ}}_B/\mathrm{f.u.}$ compared to ${\text{2.2μ}}_B/\mathrm{f.u.}$ in the ceramics. A low remanence was attributed to the presence of antiphase boundaries. A Wheatstone bridge arrangement straddling a bicrystal boundary was used to verify that spin-dependent electron transfer through a grain boundary and not an antiphase boundary is responsible for the low-field magnetoresistance found in polycrystalline samples below $T_{\mathrm{C}}.$