Thermal fluctuation aftereffect of exchange coupled films for spin valve devices

The annealing-time-dependent change in the unidirectional anisotropy field for exchange coupled films with FeMn, PdPtMn, NiMn, and NiO, which are generally used for spin valve, was investigated after thermal annealing below their blocking temperatures. It was shown that the distribution of local blocking temperature was similar for each exchange coupled film. The annealing-time-dependent change in the unidirectional anisotropy was explained by the use of thermal fluctuation aftereffect model, and the relaxation time for the anisotropy change was found to be much larger for FeMn than for PdPtMn, NiMn, and NiO, when normalizing annealing temperature by their blocking temperatures. From the viewpoint of device application, however, NiMn was proven to be the most promising antiferromagnet in terms of thermal stability because of its highest blocking temperature.