Dynamics of Composite Domain Walls in Multiferroics in Magnetic Field and Their Instability

TL;DR

This paper investigates the dynamics, structure, and instability of composite domain walls in multiferroic GdFeO3 under magnetic fields, revealing how coupling strength and field influence their behavior and splitting phenomena.

Contribution

It provides a systematic numerical and analytical study of composite domain wall dynamics, structure, and instability in multiferroics driven by magnetic fields, highlighting the effects of coupling and field strength.

Findings

DW velocity increases with magnetic field H

Splitting instability occurs at large H

Internal structure deforms with increasing c and H

Abstract

We study theoretically the dynamics of composite domain walls (DW) in multiferroic material GdFeO${}_3$ driven by magnetic field $H$. Two antiferromagnetic orders of Fe and Gd spins interact Gd-ion displacement in this system with coupling $c$ at low temperatures, and we have numerically simulated the corresponding time-dependent Ginzburg-Landau equations in which magnetic field $H$ couples to Fe-spin order parameter. We vary $H$ and $c$ systematically and calculate velocity $v$ and inner structure in a stationary state for magnetic DW and magneto-electric DW. DW mobility $v/H$ increases with $H$ and decreases with $c$ for both DWs, but their characteristics differ between the two. We have also studied analytically the smooth characteristics of magneto-electric DW by perturbation theory. Another finding is a splitting instability at large H. A magneto-electric DW splits into a pair of magnetic DW and electric DW when $c$ is large, while a magnetic DW splits when $c$ is small. Internal structure of composite DW deforms with increasing $c$ and $H$, and modulations in different order parameters separate in space. Their relative distances show a noticeable enhancement with approaching the splitting instability.