Analysis of magnetotransport properties and microstructure in current-perpendicular-to-plane pseudo spin-valves using Co₂Fe(Ga_0.5Ge_0.5) Heusler alloy and Ag/Mg-Ti-O/Ag-based spacer

Current-perpendicular-to-plane magnetoresistance (CPP-MR) devices using a Co₂Fe(Ga_0.5Ge_0.5) Heusler alloy as ferromagnetic electrodes and a Ag/Mg-Ti-O (MTO)/Ag tri-layer as a spacer are studied. A large voltage output of 16 mV with a magnetoresistance ratio of 46% and resistance-area product R_pA in the parallel magnetization state of approximately 200 mΩ μm² are obtained. The microstructure characterization reveals that upon annealing at 550 °C, nanoscale Ag channels are formed penetrating the MTO layer, which are responsible for the large MR output. At room temperature, for all the devices, R_pA decreases with increasing the bias voltage V_b, which is contradictory to the conventional CPP-giant magnetoresistance devices with a current-confined-path structure, in which the R_pA increases with increasing V_b. Such a V_b dependence of R_pA is in accordance with the temperature dependence of R_pA. These results suggest that the magneto-transport channels comprise semiconducting current confined paths, bringing new perspectives for the design and engineering of CPP-MR devices with conductive oxides-based multilayer spacers.