The influence of antiferromagnetic spin cantings on the magnetic helix pitch in cubic helimagnets

TL;DR

This paper demonstrates that antiferromagnetic spin cantings, often overlooked, can significantly influence the magnetic helix pitch in cubic helimagnets by affecting the Dzyaloshinskii-Moriya interaction parameter, with analytical and numerical agreement.

Contribution

It introduces a higher-order approximation considering spin cantings to accurately determine the D parameter affecting magnetic helix pitch.

Findings

Spin cantings significantly alter the D parameter.

Analytical expressions match numerical simulations within a few percent.

Helical wavevector k is sensitive to subtle magnetic distortions.

Abstract

In cubic helimagnets MnSi and Cu2OSeO3 with their nearly isotropic magnetic properties, the magnetic structure undergoes helical deformation, which is almost completely determined by the helicoid wavenumber k = D / J, where magnetization field stiffness J is associated with isotropic spin exchange, and D is a pseudoscalar value characterizing the antisymmetric Dzyaloshinskii-Moriya (DM) interaction. While the wavenumber can be measured directly in a diffraction experiment, the values of J and D can be calculated from the constants of pair spin interactions, which enter as parameters into the Heisenberg energy. However, the available analytical expression for D, which is of the first order in the spin-orbit coupling (SOC), has significant problems with accuracy. Here we show that hardly observable distortions of the magnetic structure, namely the antiferromagnetic spin cantings, can significantly change the constant D in the next approximation in SOC, thus affecting the wavenumber of magnetic helicoids. The obtained analytical expressions agree with the results of numerical simulation of magnetic helices in Cu2OSeO3 to within a few percent.