T=0 phase diagram and nature of domains in ultrathin ferromagnetic films with perpendicular anisotropy

TL;DR

This paper maps the zero-temperature phase diagram of ultrathin ferromagnetic films with perpendicular anisotropy, revealing four distinct domain regimes and their characteristics through variational and Monte Carlo methods.

Contribution

It provides a comprehensive analysis of the ground states and domain structures across the full parameter space, including the nature of domain walls and the spin reorientation transition.

Findings

Identifies four regimes: Ising, saturated stripe, canted, and in-plane ferromagnetic.

Describes how domain width varies with anisotropy and interactions.

Details the nature of domain walls and the spin reorientation transition.

Abstract

We present the complete zero temperature phase diagram of a model for ultrathin films with perpendicular anisotropy. The whole parameter space of relevant coupling constants is studied in first order anisotropy approximation. Because the ground state is known to be formed by perpendicular stripes separated by Bloch walls, a standard variational approach is used, complemented with specially designed Monte Carlo simulations. We can distinguish four regimes according to the different nature of striped domains: a high anisotropy Ising regime with sharp domain walls, a saturated stripe regime with thicker walls inside which an in-plane component of the magnetization develops, a narrow canted-like regime, characterized by a sinusoidal variation of both the in-plane and the out of plane magnetization components, which upon further decrease of the anisotropy leads to an in-plane ferromagnetic state via a spin reorientation transition (SRT). The nature of domains and walls are described in some detail together with the variation of domain width with anisotropy, for any value of exchange and dipolar interactions. Our results, although strictly valid at $T=0$, can be valuable for interpreting data on the evolution of domain width at finite temperature, a still largely open problem.