Effect of an Fe–Si buffer layer on the magnetoresistance of a Co/Cu multilayer

Abstract

Co/Cu multilayers were fabricated on a thermally oxidized Si wafer (SiO2 substrate) as well as a bare Si wafer (Si substrate). The multilayer had an Fe buffer layer and was produced in a sputtering atmosphere into which oxygen was introduced. In the case of the Si substrate, the magnetoresistance (MR) ratio increased as the partial oxygen pressure decreased below 3×10−8 Torr, whereas it steeply decreased in the case of the SiO2 substrate. The increase in the MR ratio in the case of the Si substrate was due to an enlargement of the lateral grain size of the multilayers, which reduced the interfacial roughness of the multilayer. When Fe–Si was used as the buffer layer, the MR ratio of the multilayer on the SiO2 substrate drastically changed in relation to the buffer layer’s Si content. A maximum MR ratio of 40% was obtained at 16% Si, corresponding to the enlargement in the lateral grain size. The MR ratio of the multilayer fabricated on the Fe82Si18 buffer layer remained 28% after annealing at 350 °C. We therefore conclude that the Fe–Si buffer layer is effective in facilitating the lateral grain growth of Co/Cu multilayers and in attaining high thermal stability of the MR ratio.