Domain Walls in Helical Magnets: Elasticity and Pinning

TL;DR

This paper investigates the elastic and pinning properties of novel domain walls in helical magnets, revealing how vortex-free walls are stiff with suppressed impurity pinning, while vortex-containing walls are more flexible and strongly pinned.

Contribution

It provides the first detailed calculation of the elasticity and pinning characteristics of these new domain walls, using the pitch angle as a small parameter.

Findings

Vortex-free domain walls are very stiff and have long-range elasticity.

Vortex-containing domain walls exhibit short-range elasticity and strong impurity pinning.

Roughening transition temperature is around the N9el temperature.

Abstract

Recently completely new types of domain walls (DWs) have been discovered in helical magnets, consisting generically of a regular array of {\it pairs} of magnetic vortex lines \cite{Li+12}. Only for special orientations DWs are free of vortices. In this article we calculate their elastic and pinning properties, using the pitch angle $\theta$ as a small parameter. In particular we show that vortex free DWs exhibit long range elasticity which makes them very stiff and suppresses their pinning by impurities. Their roughening transition temperature is of the order of the N\'eel temperature. DWs including vortices (either by orientation or due to step formation above their roughening transition) show short range elasticity and strong pinning by impurities. These results apply both to centro-symmetric as well as to non-centrosymmetric systems. The application to chiral liquid crystals is briefly discussed.