Non-collinear Magnetic Configurations at Finite Temperature in Thin Films

TL;DR

This study investigates how finite temperature affects magnetic configurations in thin monolayer films, revealing that Dzyaloshinsky-Moriya interactions can destabilize collinear order and induce non-collinear states, with external fields and finite size effects influencing stability.

Contribution

It introduces a comprehensive model combining various interactions to analyze temperature-dependent magnetic states and demonstrates the transition from collinear to non-collinear configurations.

Findings

Increasing Dzyaloshinsky-Moriya interaction lowers the critical temperature for collinear order

External magnetic fields stabilize ferromagnetic states at finite temperatures

Finite size effects at edges stabilize spin spiral states by fixing phase

Abstract

The finite-temperature magnetism of a monolayer on a bcc (110) surface was examined using a model Hamiltonian containing ferromagnetic or antiferromagnetic exchange interactions, Dzyaloshinsky-Moriya interactions and easy-axis on-site anisotropy. We examined the competition between the collinear ground state parallel to the easy axis and the spin spiral state in the plane perpendicular to this axis preferred by the Dzyaloshinsky-Moriya interaction. Using approximative methods to calculate the magnon spectrum at finite temperatures, it was found that even if the ground state is collinear, increasing the Dzyaloshinsky-Moriya interaction strongly decreases the critical temperature where this collinear order disappears. Using atomistic spin dynamics simulations it was found that at this critical temperature the system transforms into the non-collinear state. Including external magnetic field helps stabilising the ferromagnetic state. An effect due to the finite size of the magnetic monolayer was included in the model by considering a different value for the anisotropy at the edges of the monolayer. This effect was shown to stabilize the spin spiral state by fixing the phase at the ends of the stripe.