Models for the magnetic ac susceptibility of granular superferromagnetic CoFe/Al$_2$O$_3$

TL;DR

This paper uses numerical simulations to analyze the magnetic ac susceptibility of superferromagnetic CoFe/Al₂O₃, revealing domain wall dynamics similar to disordered ferromagnets and matching experimental observations.

Contribution

It introduces models for driven domain wall dynamics in superferromagnetic systems that replicate experimental Cole-Cole plot features.

Findings

Simulated Cole-Cole plots match experimental data.

Domain wall motion exhibits pinning and sliding behavior.

Models successfully reproduce superferromagnetic susceptibility features.

Abstract

The magnetization and magnetic ac susceptibility, $\chi = \chi' - i \chi''$, of superferromagnetic systems are studied by numerical simulations. The Cole-Cole plot, $\chi''$ vs. $\chi'$, 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 Co$_{80}$Fe$_{20}$/Al$_{2}$O$_{3}$ 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.