スピンバルブ膜の構造と磁気特性に影響を及ぼすＴａ／Ｎｉ‐Ｆｅ下地層の成長過程

Abstract

The structure and magnetic properties of Mn-Ir/Co-Fe based bottom-type spin valves (SVs) were investigated as a function of the under-layer thickness. Surface morphology of Ta/Ni-Fe under layers was also investigated with in-situ STM. The SV characteristics, such as magnetoresistance (MR) ratio and interlayer ferromagnetic coupling field (Hin), strongly depend on the underlaid Ni-Fe thickness (dNi-Fe). The MR ratio gradually increases with decreasing dNi-Fe above 20 A because of the reduction of shunting current in the Ni-Fe layer. On the contrary, the MR ratio decreases with decreasing dNi-Fe below 20 A. The Hin drops below 20 A of dNi-Fe and shows relatively small values (10 to 20 Oe). These changes of SV characteristics correspond closely to change in film structure: a strong fcc (111) texture of the SV is observed when dNi-Fe = 20 A, but it vanishes when dNi-Fe < 20 A, meaning the grain size is reduced. The surface morphology of a Ta/Ni-Fe under layer also changes drastically at dNi-Fe = 20 A. Distinct grains are observed on the surface of the dNi-Fe under layer on Ta only when dNi-Fe = 20 A. This indicates that inter-diffusion of the Ni-Fe layer is less than 20 A thick with a Ta layer. We conclude that the drastic change of film structure resulting in the change of SV characteristics is due to the inter-diffused Ni-Fe-Ta layer, which promotes the grain growth of the remaining Ni-Fe layer and the SV grown on it.