Magnetic states of discontinuous Co80Fe20–Al2O3 multilayers

Abstract Discontinuous metal–insulator multilayers [Co 80 Fe 20 ( t )/Al 2 O 3 (3 nm)] n were studied by SQUID magnetometry and AC susceptometry. CoFe forms ferromagnetic particles in the Al 2 O 3 matrix. In this paper, we focus on the field dependence of the AC susceptibility of samples with t =1.3 nm. We find strong evidence for transitions from a superpara- to a superferromagnetic and, finally, to a reentrant superspin glass state.