A Superparamagnetic State Induced by a Spin Reorientation Transition in Ultrathin Magnetic Films

TL;DR

This paper uses Monte-Carlo simulations to study spin reorientation transitions in small ultrathin magnetic films, revealing a superparamagnetic state characterized by dynamical fluctuations at the transition temperature.

Contribution

It demonstrates that the SRT in small ultrathin films involves a superparamagnetic state, contrasting with static domain structures in larger films, providing new insights into magnetic phase transitions.

Findings

Superparamagnetic state observed at SRT temperature.

Magnetization disappearance due to dynamical fluctuations.

Contrast with static domain behavior in larger films.

Abstract

We investigate a spin reorientation transition (SRT) in ultrathin magnetic films by Monte-Carlo simulations. We assume that the lateral size of the film is relatively small and it has a single-domain structure. To gain insights into the SRT, we measure a free-energy as a function of perpendicular and in-plane magnetizations. As a result, we find that the system is in a superparamagnetic state at the SRT temperature. The disappearance of magnetization around the SRT temperature, which is observed in experiments, emerges due to dynamical fluctuations in magnetization which are inherent in the superparamagnetic state. This observation is in contrast to that in large ultrathin magnetic films that the disappearance of magnetization is caused by a static magnetic structure with many complex domains.