Charge transfer processes and magnetoresistance in strontium ferromolybdate with dielectric barriers

The Sr 2 FeMoO 6− δ compound attracts the attention of researchers due to a high Curie temperature, large values of negative magnetoresistance at room temperature and a practically 100% spin polarization of conduction electrons. We have studied the role of grain boundaries on the electrical transport in Sr 2 FeMoO 6− δ in applied magnetic fields up to 8 T. The compound was synthesized out of partially reduced SrFeO 3− x , SrMoO 4− y precursors (sample I). At the first oxidation stage upon annealing at 700 K in argon with a partial oxygen pressure p (O 2 ) = 10 Pa for 15 h (sample II), the internal structure of the Sr 2 FeMoO 5.82 grains did not change. Sample II exhibits a mixed type of electrical conduction. In a magnetic field B its resistivity decreases without changing the mixed regime of charge transport, only shifting the temperature of minimum resistivity ( T mB ) to lower values. At temperatures above T mB the conductivity is predominantly metallic, whereas below T mB down to 4.2 K it is of semiconductor type. The increase of the annealing time up to 30 h (sample III) brings about an increase of the resistivity and the appearance of semiconductor‐type conductivity at T  = 300–4.2 K, which indicates the formation of a continuous insulating interlayer between the grains. In a magnetic field, the resistivity decreases, with the conductivity changing from the semiconducting to a mixed one. In the latter case the charge transport can occur both through point metallic contacts and by means of spin‐dependent tunneling across dielectric interlayers between Sr 2 FeMoO 5.82 grains.