Improved current-perpendicular-to-plane giant magnetoresistance outputs by heterogeneous Ag-In:Mn-Zn-O nanocomposite spacer layer prepared from Ag-In-Zn-O precursor

Abstract

A precursor material Ag-In-Zn-O (AIZO) for the spacer layer of current-perpendicular-to-plane giant magnetoresistance devices has been developed. A pseudo-spin-valve structure with polycrystalline Co2(Mn0.6Fe0.4)Ge (CMFG) Heusler alloy ferromagnetic layers and a AIZO spacer precursor exhibited a large magnetoresistance ratio (ΔR/R) up to 54% at a resistance-area product (RA) of ∼0.075 ω μm2 and a maximum output voltage of ∼18 mV. Cross-sectional scanning transmission electron microscopy observations revealed that the spacer layer was not uniform but had a heterogeneous Ag-In:Mn-Zn-O nanocomposite structure, which is considered to have formed by the oxidation of Mn diffused from the CMFG layers and by the reduction of In2O3 to metallic In alloyed with Ag. Due to the current-confinement effect through the fcc Ag-In metallic path (current-confined-path, CCP) with the average lateral size of ∼7 nm surrounded by a rocksalt Mn-Zn-O matrix, both RA and ΔR/R were enhanced compared to the case with the uniform AgSn alloy spacer layer. A Ag/IZO bilayer precursor also formed a similar Ag-In:Mn-Zn-O nanocomposite spacer with a lateral size of the Ag-In CCPs of ∼3 nm, and the device with the Ag/IZO precursor showed ΔR/R ∼30%. The difference in ΔR/R between the AIZO and Ag/IZO precursors can be explained by the matching of effective spin resistance between the CMFG ferromagnetic layers and the Ag-In CCP with different sizes. The resistance dispersion of the devices was also analyzed both experimentally and theoretically.