Domain walls, canted states and stripe width variation in ultrathin magnetic films with perpendicular anisotropy

TL;DR

This study investigates the relationship between domain wall structures and stripe width variation in ultrathin magnetic films with perpendicular anisotropy, using a 2D Heisenberg model, Monte Carlo simulations, and extending classic theoretical results.

Contribution

It provides a comprehensive zero temperature phase diagram for the model, revealing how domain wall structures and stripe widths vary with anisotropy, especially near the Spin Reorientation Transition.

Findings

Canted state becomes the ground state near SRT for all exchange/dipolar ratios.

Stripe width variation correlates with domain wall width changes as anisotropy varies.

Yafet & Gyorgy approximation describes domain walls near SRT, but deviations occur at high anisotropy.

Abstract

Stripe width variation in ultrathin magnetic films is a well known phenomenon still not well understood. We analyze this problem considering a 2D Heisenberg model with ferromagnetic exchange interactions, dipolar interactions and perpendicular anisotropy, relevant e.g. in Fe/Cu(001) films. By extending a classic result of Yafet & Gyorgy (YG) and using Monte Carlo simulations we calculate the complete zero temperature phase diagram of the model. Through this calculation we analyze the correlation between domain walls structure and stripe width variation, as the perpendicular anisotropy changes. In particular, we found evidences that the recently detected canted state becomes the ground state of the system close to the Spin Reorientation Transition (SRT) for any value of the exchange to dipolar couplings ratio. Far away of the SRT the canted ground state is replaced by a saturated stripes state, in which in--plane magnetization components are only present inside the walls. We find that the domain wall structure strongly depends on the perpendicular anisotropy: close to SRT it is well described by YG approximation, but a strong departure is observed in the large anisotropy limit. Moreover, we show that stripe width variation is directly related to domain wall width variation with the anisotropy.