Magnetoresistance in nanosize strontium ferromolybdate with dielectric interlayers

Single phase strontium ferromolybdate nanopowder with a double perovskite structure has 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 4.2 to 300 K range changes from a metal type one in the single phase Sr2FeMoO6−δ to a semiconductor type one in the Sr2FeMoO6−δ – SrMoO4 – Sr2FeMoO6−δ structure containing dielectric interlayers, indicating variable charge hopping in the latter structure. 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 barriers in the granular Sr2FeMoO6−δ – SrMoO4 – Sr2FeMoO6−δ heterostructure.

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