Buffer layer dependence of magnetoresistance effects in Co₂Fe_0.4Mn_0.6Si/MgO/Co₅₀Fe₅₀ tunnel junctions

Buffer layer dependence of tunnel magnetoresistance (TMR) effects was investigated in Co₂Fe_0.4Mn_0.6Si (CFMS)/MgO/Co₅₀Fe₅₀ magnetic tunnel junctions (MTJs). Pd, Ru and Cr were selected for the buffer layer materials, and MTJs with three different CFMS thicknesses (30, 5, and 0.8 nm) were fabricated. A maximum TMR ratio of 136% was observed in the Ru buffer layer sample with a 30-nm-thick CFMS layer. TMR ratios drastically degraded for the CFMS thickness of 0.8 nm, and the values were 26% for Cr buffer layer and less than 1% for Pd and Ru buffer layers. From the annealing temperature dependence of the TMR ratios, amounts of interdiffusion and effects from the lattice mismatch were discussed.