Composition dependent magnetic coupling in Fe-Cr alloy cluster arrays^†

Dense arrays of Fe-Cr alloy clusters with different Cr ratios were fabricated by gas-phase cluster beam deposition. The complex multiphase structure and various coupling effects in the cluster arrays were studied. A lattice mismatched tetragonal-like morphology of the Fe-Cr alloy cluster was observed at large Cr ratio. An exchange bias effect was observed and was shown to be dependent on the proportion of the Cr components in the alloy. With the increase of the Cr composition, the exchange bias field became smaller and stronger dipolar interactions between the clusters developed. Residual coercivity and magnetization, which were more remarkable in the tetragonal-like clusters, were observed above the ferromagnetic-superparamagnetic transition temperature. The experimental results of the coercive field and the bias field at different temperatures demonstrated that the tetragonal-like clusters had better thermal stability and greater anisotropy.