# Temperature scaling of the Dzyaloshinsky-Moriya interaction in the spin wave spectrum

## TL;DR

This paper derives universal formulas for how the Dzyaloshinsky-Moriya interaction and other magnetic parameters scale with temperature in ferromagnetic systems, linking atomistic models to macroscopic spin wave spectra.

## Contribution

It introduces a Green's function approach to calculate temperature-dependent spin wave spectra and establishes a connection between atomistic interactions and micromagnetic parameters.

## Key findings

- Universal temperature scaling expressions for Dzyaloshinsky-Moriya interaction and exchange stiffness.
- Anisotropy-like term emerges in the spectrum due to thermal fluctuations and Dzyaloshinsky-Moriya interaction.
- Good agreement between theoretical predictions and Monte Carlo simulations.

## Abstract

The temperature scaling of the micromagnetic Dzyaloshinsky-Moriya exchange interaction is calculated for the whole range of temperature. We use Green's function theory to derive the finite-temperature spin wave spectrum of ferromagnetic systems described by a classical atomistic spin model Hamiltonian. Within this model, we find universal expressions for the temperature scaling not only of the Dzyaloshinsky-Moriya interaction but also of the Heisenberg exchange stiffness and the single-ion anisotropy. In the spirit of multiscale models, we establish a clear connection between the atomistic interactions and the temperature-dependent coefficients in the spin wave spectrum and in the micromagnetic free energy functional. We demonstrate that the corrections to mean-field theory or the random phase approximation for the temperature scaling of Dzyaloshinsky-Moriya and Heisenberg exchange interactions assume very similar forms. In the presence of thermal fluctuations and Dzyaloshinsky-Moriya interaction an anisotropy-like term emerges in the spin wave spectrum which, at low temperature, increases with temperature, in contrast to the decreasing single-ion anisotropy. We evaluate the accuracy of the theoretical method by comparing it to the spin wave spectrum calculated from Monte Carlo simulations.