The microstructural origin of the enhanced current-perpendicular-to-the-plane giant magnetoresistance by Ag/In-Zn-O/Zn spacer layer

Abstract

The mechanism of the enhancement of the current-perpendicular-to-the-plane giant magnetoresistance ratio (ΔR/R) by a Ag/In-Zn-O (IZO)/Zn spacer layer for the spin-valves with Co2(Mn0.6Fe0.4)Ge Heusler alloy ferromagnetic layers was investigated. The insertion of a thin Ag (0.2-0.6 nm) layer below the IZO layer was found to be critical for achieving relatively low resistance-area product (RA) ∼ 0.1 Ω μm2 and large ΔR/R up to 22%. Structural characterizations by scanning transmission electron microscopy revealed that the actual spacer layer was an inhomogeneous Ag-In:Mn-Zn-O nanocomposite, where the Ag-In is thought to play a role in current-confined-path (CCP) for electric current, and the Mn-Zn-O is an oxide matrix which forms by Mn diffusion from the Co2(Mn0.6Fe0.4)Ge layers and oxidation by In2O3 in IZO. The enhancement of ΔR/R is explained to be due to the current confinement through the Ag-In CCPs in the Ag-In:Mn-Zn-O nanocomposite spacer, and the lower RA values (0.065-0.011 Ω μm2) for the Ag-In:Mn-Zn-O CCP-spacer than those for the conventional Cu:AlOx CCP-spacer can be understood by assuming a lower resistivity in the Ag-In CCPs.