Interlayer diffusion and specularity aspects of amorphous CoNbZr-based spin-valves

Interlayer diffusion, thermal stability, and specular scattering behaviors of spin-valves (SV) where CoNbZr films were employed in as under and capping layers have been investigated. CoNbZr 2 (or Ta 5)/CoFe/Cu/CoFe/IrMn/CoNbZr 0∼10 (or Ta 5) nm stacks were sputter-deposited on Si/SiO₂ substrates. Both normalized MR ratio and exchange bias field (H_ex) of a conventional Ta-based SV decreased monotonically about 50% upon exposure to postdeposition annealing at 300°C. On the contrary, these values increased about 50% for CoNbZr-based SVs, in particular, as CoNbZr capping thickness was less than 4 nm. Surface depth profiling results suggest that Mn diffused into the pinned CoFe layer (inward) but not into the Ta capping layer (outward) for the Ta-based SV. Unlike in the Ta capping case, a CoNbZr capping layer promoted outward Mn diffusion resulting in a formation of thin Mn-oxide layer at the surface. We attribute the increase of MR ratio in CoNbZr-capped SVs to enhanced specularity due to the presence of thin Mn-oxide. However, the specular scattering effect is reduced by increasing the thickness of CoNbZr capping layer.