Magnetoresistive effect in nanosized strontium ferromolybdate with dielectric interlayers

Monophasic iron ferromolybdate nanopowders with a double perovskite structure have been synthesized using the citrate-gel technique at pH=4. A superstructural ordering degree of the iron and molybdenum cations of 88% has been obtained. X-ray diffraction of pressed Sr2FeMoO6−δ pellets subjected to annealing at T=700 K and p(O2)=10 Pa has revealed the formation of the SrMoO4 phase at grain boundaries. The temperature dependence of the electrical resistivity in the range from 4.2 to 300 K switches from a metal type one in the monophasic Sr2FeMoO6-δ to a semiconductor type one in the Sr2FeMoO6−δ-SrMoO4-Sr2FeMoO6−δ structure containing dielectric interlayers, indicating variable range hopping in the latter. In the applied magnetic fields the temperature dependence does not change qualitatively; however, the resistivity decreases with increasing field, i.e., a negative magnetoresistance of up to 41% at T=10 K and B=8 T is observed. The external field forms a collinear spin structure, thus increasing the spin-polarized current through the granular Sr2FeMoO6−δ-SrMoO4-Sr2FeMoO6−δ heterostructure.