Charge transfer mechanisms in strontium ferromolybdate with tunneling barriers

The single-phase strontium ferromolybdate powder with the double perovskite structure has been synthesized by the citrate-gel method with superstructural ordering of iron and molybdenum cations of 88%. The formation of the SrMoO₄ phase on the intergrain boundaries has been determined by means of the XRD studies, the Electrokinetic Sonic Analysis technique, and FESEM investigations of pressed Sr₂FeMoO_6-δ powders subjected to the isothermic treatment at 700 K and p(O₂) = 10 Pa. The temperature dependence of the electrical resistivity in the temperature range 4.2–300 K has a metallic type in the single-phase Sr₂FeMoO_6-δ compound and the semiconductor type in the Sr₂FeMoO_6-δ–SrMoO₄–Sr₂FeMoO_6-δ structure with dielectric sheaths. In the latter case, a hopping mechanism of charge transfer is observed. In the applied magnetic field, the temperature dependence does not change qualitatively; however, the resistivity decreases with increasing field, i.e., a negative magnetoresistive effect appears, reaching 43.6% at 10 T and 10 K. The external field forms a collinear spin structure, thus increasing the spin-polarized current through the energy barriers in the granular Sr₂FeMoO_6-δ–SrMoO₄–Sr₂FeMoO_6-δ heterostructure.