Effect of new materials as under and cap layers on thermal stability of synthetic bottom spin valves

We investigated the thermal stability of the Ta-, ZrAl- and TiAl-based synthetic bottom spin valves. In the as-deposited state, the MR ratios of ZrAl- and TiAl-based synthetic SVs (SSV) are similar to that of the Ta-based SV. However, after annealed at 400 °C for 10 min, the MR ratio of Ta-based SV decreased by 42.5% (from 7.43% to 4.27%). On the other hand, the MR ratio of ZrAl- and TiAl-based SSVs increased 0.3% (from 7.37% to 7.39%) and 13.3% (from 7.47% to 8.46%), respectively. Auger depth profile clearly showed that ZrAl- and TiAl-based SSVs have higher interdiffusion resistance than Ta-based SV. Especially, diffusion of Mn from antiferromagnet layer to pinned layer was suppressed in TiAl-based SVs. The root-mean-square (RMS) roughness of the TiAl layer (0.11 nm) was much smaller than those of the ZrAl (0.16 nm) and Ta layer (0.43 nm). Due to high affinity of Ti or Al with oxygen, very stable and dense TiAl-oxides were formed at the surface during annealing. Thermal stability of TiAl- and ZrAl-based SSVs was enhanced due to surface uniformity and high passivity of TiAl- and ZrAl-oxides.