Distribution of blocking temperatures in nano-oxide layers of specular spin valves

Specular spin valves show enhanced giant magnetoresistive (GMR) ratio when compared to other, simpler, spin valve structures. The enhancement of GMR results from specular reflection in nano-oxide layers (NOLs) formed by the partial oxidation of the pinned and free layer. These oxides forming the NOL order antiferromagnetically (AFM) below a temperature T similar to 175 K. Here, we study the effects of the pinned layer magnetization and its domain structure on the AFM ordering of the NOL by performing field cooling measurements with different cooling fields (H-0). We observe enhanced (reduced) exchange field and magnetoresistive ratio for H-0 > 0 (< 0), i.e., parallel (antiparallel) to the pinned magnetization. These measurements allowed us to confirm the existence of a wide distribution of blocking temperatures (T-B) in the NOL of specular spin valves, having a maximum at T approximate to 175 K, and extending to NOL regions with T-B as low as 15 K. (c) 2007 American Institute of Physics.