Observation and formation mechanism of 360{\deg} domain wall rings in Synthetic Anti-Ferromagnets with interlayer chiral interactions

TL;DR

This study reveals the formation of 360-degree domain wall rings in synthetic antiferromagnets caused by interlayer Dzyaloshinskii-Moriya interactions, highlighting their potential impact on spintronic device development.

Contribution

It provides nanoscale imaging and analysis of spin textures induced by IL-DMI, demonstrating the conditions for domain wall ring formation in SAFs.

Findings

360° domain wall rings observed with magnetic imaging

Ring formation occurs when IL-DMI exchange bias is partially compensated

Non-zero remanent effective field is necessary for ring stability

Abstract

The Interlayer Dzyaloshinskii-Moriya interaction (IL-DMI) chirally couples spins in different ferromagnetic layers of multilayer heterostructures. So far, samples with IL-DMI have been investigated utilizing magnetometry and magnetotransport techniques, where the interaction manifests as a tunable chiral exchange bias field. Here, we investigate the nanoscale configuration of the magnetization vector in a synthetic anti-ferromagnet (SAF) with IL-DMI, after applying demagnetizing field sequences. We add different global magnetic field offsets to the demagnetizing sequence in order to investigate the states that form when the IL-DMI exchange bias field is fully or partially compensated. For magnetic imaging and vector reconstruction of the remanent magnetic states we utilize X-ray magnetic circular dichroism photoemission electron microscopy, evidencing the formation of 360$^{\circ}$ domain wall rings of typically 0.5-3.0 $\mu m$ in diameter. These spin textures are only observed when the exchange bias field due to the IL-DMI is not perfectly compensated by the magnetic field offset. From a combination of micromagnetic simulations, magnetic charge distribution and topology arguments, we conclude that a non-zero remanent effective field with components both parallel and perpendicular to the anisotropy axis of the SAF is necessary to observe the rings. This work shows how the exchange bias field due to IL-DMI can lead to complex metastable spin states during reversal, important for the development of novel spintronic devices.