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

Thin films of (001)-oriented Sr₂FeMoO₆ have been epitaxially deposited or LaAlO₃ and SrTiO₃ (001) substrates by pulsed laser deposition. The deposition conditions were optimized. Single-phase Sr₂FeMoO₆ 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 3.2μ_B/f.u. However, the Curie temperature T_C≈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 1.5μ_B/f.u. compared to 2.2μ_B/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_C.