Robust Formation of Ultrasmall Room-Temperature Ne\'el Skyrmions in Amorphous Ferrimagnets from Atomistic Simulations

TL;DR

This study demonstrates through atomistic simulations that ultrasmall Neel skyrmions can be stabilized at room temperature in amorphous ferrimagnets with moderate DMI, enabling higher density spintronic devices.

Contribution

It reveals that stable, ultrasmall skyrmions can exist in thicker films with reduced DMI, challenging previous assumptions about the need for large DMI for stability.

Findings

Ultrasmall skyrmions are stabilized at room temperature in 15 nm thick GdCo films.

Reducing DMI below that of Pt still maintains skyrmion stability.

Skyrmions retain uniform shape across film thickness despite DMI decay.

Abstract

Ne\'el skyrmions originate from interfacial Dzyaloshinskii Moriya interaction (DMI). Recent studies have explored using thin-film ferromagnets and ferrimagnets to host Ne\'el skyrmions for spintronic applications. However, it is unclear if ultrasmall (10 nm or less) skyrmions can ever be stabilized at room temperature for practical use in high density parallel racetrack memories. While thicker films can improve stability, DMI decays rapidly away from the interface. As such, spins far away from the interface would experience near-zero DMI, raising question on whether or not unrealistically large DMI is needed to stabilize skyrmions, and whether skyrmions will also collapse away from the interface. To address these questions, we have employed atomistic stochastic Landau-Lifshitz-Gilbert simulations to investigate skyrmions in amorphous ferrimagnetic GdCo. It is revealed that a significant reduction in DMI below that of Pt is sufficient to stabilize ultrasmall skyrmions even in films as thick as 15 nm. Moreover, skyrmions are found to retain a uniform columnar shape across the film thickness despite the decaying DMI. Our results show that increasing thickness and reducing DMI in GdCo can further reduce the size of skyrmions at room temperature, which is crucial to improve the density and energy efficiency in skyrmion based devices.