Intragrain and intergrain magnetoresistance In Mn, Fe/Mo and Co simple, double and oxygen deficient perovskite oxides

Abstract Several different transition metal oxides with structures derived from the perovskite show magnetoresistance (MR) properties. Both Ln 1− x A x MnO 3 manganites and Sr 2 FeMoO 6 double-perovskites exhibit two kinds of MR: intrinsic (intragrain) in the vicinity of their Curie temperature T C and extrinsic (intergrain) below T C . The former one, colossal in the case of manganites, requires large magnetic field values (tesla or above) whereas the second one, which originates in the tunneling across a barrier (grain-boundary) of the spin-polarized carriers, is shown even in low magnetic fields. The origin of MR properties of Ln 1− x A x CoO 3−δ cobaltites differs from that of the Mn and Fe/Mo-based oxides. In particular, no low-field MR is shown.