Models for the magnetic ac susceptibility of granular superferromagnetic CoFe/Al2O3 -: art. no. 214432

The magnetization and magnetic ac susceptibility, chi=chi(')-ichi('), of superferromagnetic systems are studied by numerical simulations. The Cole-Cole plot, chi(') versus chi('), is used as a tool for classifying magnetic systems by their dynamical behavior. The simulations of the magnetization hysteresis and the ac susceptibility are performed with two approaches for a driven domain wall in random media. The studies are motivated by recent experimental results on the interacting nanoparticle system Co80Fe20/Al2O3 showing superferromagnetic behavior. Its Cole-Cole plot indicates domain-wall motion dynamics similarly to a disordered ferromagnet, including pinning and sliding motion. With our models, we can successfully reproduce the features found in the experimental Cole-Cole plots.