Interlayer coupling in spin valve structures

The effect of structural imperfections such as interface roughness and layer strain on the sign and amplitude of the interlayer coupling between the two ferromagnetic layers of exchanged-biased NiFe/Cu/NiFe/FeMn spin valves is discussed. Two distinct regimes are found: when the NiFe-Cu interface is smooth, with a mean roughness smaller that 4 /spl Aring/, the interlayer coupling shows a distinct oscillatory behavior, with a period of /spl Lambda/=13.5 /spl Aring/, and can be well described by a RKKY-like exchange based mechanism. As the amplitude of the interface roughness increases the magnetostatic-type Neel's orange peel coupling becomes more important, and the ferromagnetic component of the coupling is enhanced. The higher than expected period of oscillation, observed in these spin valves, is explained in terms of a strain induced effect.