The Spin Reorientation Transition and Phase Diagram of Ultrathin Ferromagnetic Films

TL;DR

This study uses Monte Carlo simulations to map the phase diagram of ultrathin ferromagnetic films, revealing spin reorientation transitions and phase behaviors consistent with experimental observations.

Contribution

It provides a comprehensive phase diagram for ultrathin films considering anisotropy and temperature, including the characterization of spin reorientation transitions and comparison with experimental data.

Findings

Identification of a line of Spin Reorientation Transitions.

Observation of a paramagnetic gap between phases.

Similar phase behavior in dipolar-only systems.

Abstract

We show results from Monte Carlo simulations of a two dimensional Heisenberg model for ultrathin films with perpendicular anisotropy. A complete phase diagram is obtained as a function of anisotropy and temperature, spanning a wide range of behavior. We discuss our results in relation with experimental findings in different ultrathin films. We observe and characterize a line of Spin Reorientation Transitions . This transition from out of plane stripe order to in plane ferromagnetic order presents a paramagnetic gap in between in a finite region in parameter space, as reported in experiments. For large anisotropies direct transitions from a low temperature stripe phase to a paramagnetic or tetragonal phase with dominant perpendicular magnetization is observed, also in agreement with experiments. We also show the phase diagram for a system without exchange, i.e. with pure dipolar and anisotropy interactions. It shows a similar behavior to the ferromagnetic case with antiferromagnetic instead of stripe phases at low temperatures. A Spin Reorientation Transition is also found in this case.