Thermal and Mn diffusion behaviors of CoNbZr-based spin valves with nano oxide layers

The authors investigated the specularity and thermal characteristics of CoNbZr-based spin valves (SVs) with and without employing nano oxide layers (NOL). Both CoNbZr- and Ta-based SV films composed of Si-SiO₂-CoNbZr (or Ta)-CoFe-NOL-CoFe-Cu-CoFe-IrMn-CoNbZr (or Ta) were prepared by rf magnetron sputtering. Magnetoresistance (MR) ratios in the as-deposited state increased 48% (3.4% → 5.0%) with incorporation of NOL. In particular, a remarkable enhancement (about 95%) in the MR ratio after annealing at 300°C for 20 min was observed (5.0% → 9.8%). According to the Auger electron spectroscopy depth profile, the large increase of the MR ratios in the initial stage of annealing were due to the double specular scattering effects by the Mn-oxides at the surface and the NOL in the free layer. Due to high affinity of Mn for oxygen, Mn diffused preferentially to the position of high oxygen potential (such as the surface or the NOL) during prolonged annealing. The authors could artificially control the diffusion direction of Mn by providing an oxygen potential (like inserting NOL) in the SV structure.