Antiferromagnetic Domain Structure in Bilayer Manganite

TL;DR

This study uses soft x-ray nanodiffraction to reveal unique antiferromagnetic domain patterns in bilayer manganite, showing domain memory, walls along crystallographic directions, and a ripple structure possibly caused by inversion symmetry loss.

Contribution

It provides the first detailed imaging of antiferromagnetic domains in bilayer manganite, highlighting domain memory, wall orientation, and a ripple pattern linked to symmetry breaking.

Findings

Domains are quenched with intrinsic spin memory.

Domain walls align with crystallographic directions.

Ripple pattern in spin structure suggests Dzyaloshinskii-Moriya interaction.

Abstract

We report a novel soft x-ray nanodiffraction study of antiferromagnetic domains in the strongly correlated bylayer manganite La$_{0.96}$Sr$_{2.04}$Mn$_{2}$O$_{7}$. We find that the antiferromagnetic domains are quenched, forming a unique domain pattern with each domain having an intrinsic memory of its spin direction, and with associated domain walls running along crystallographic directions. This can be explained by the presence of crystallographic or magnetic imperfections locked in during the crystal growth process which pin the antiferromagnetic domains. The antiferromagnetic domain pattern shows two distinct types of domain. We observe, in one type only, a periodic ripple in the manganese spin direction with a period of approximately 4 \micro\meter. We propose that the loss of inversion symmetry within a bilayer is responsible for this ripple structure through a Dzyaloshinskii-Moriya-type interaction.