Superferromagnetic domain state dynamics in discontinuous CoFe/Al2O3 multilayers

Abstract Magnetization hysteresis and AC susceptibility measurements were performed on the discontinuous metal–insulator multilayer [Co 80 Fe 20 (1.4 nm)/Al 2 O 3 (3 nm)] 10 . CoFe forms ferromagnetic single-domain particles being embedded in the Al 2 O 3 matrix. Due to strong dipolar inter-particle interactions a “superferromagnetic” correlation of particle moments was previously stated. The dynamical magnetic properties of the superferromagnet can be understood in the framework of domain wall motion in an impure ferromagnet. Kinetic simulations are employed, which are based on field and temperature-dependent domain wall velocities. The magnetization hysteresis as well as the AC susceptibility, χ′−iχ′′ , are calculated and compared to our experimental results and yield a good agreement. The analysis of the Cole–Cole plots, χ′′ vs. χ′ , is particularly interesting. They are shown to serve as fingerprints for the different dynamic behavior as claimed previously.