Magneto-optical study of exchange spring degradation

Magnetic structures of SmCo/Fe bilayers during remagnetization and after mu ltiple field cycling are studied magneto-optically (MO). Rotation of the re manent magnetization in the soft Fe layer away from the easy axis is found after large enough remagnetizing fields. This is indicative of the appearan ce of biquadratic coupling between the layers. It is explained by the fluct uation exchange mechanism due to the field induced magnetic inhomogeneity o f the hard layer. Such an inhomogeneity revealed in the MO patterns also ex plains the degradation of the bias field in exchange springs.