Spin polarized STM imaging of nanoscale N\'eel skyrmions in an SrIrO3/SrRuO3 Perovskite Bilayer

TL;DR

This study uses spin-polarized STM to directly image nanoscale Ne9el skyrmions in a SrIrO3/SrRuO3 bilayer, revealing their size, shape, and localization within the SrIrO3 regions, advancing understanding of interfacial spin textures.

Contribution

The paper demonstrates direct imaging of nanoscale Ne9el skyrmions in an oxide bilayer, highlighting their size, distribution, and dependence on interfacial spin-orbit coupling, which is a novel observation.

Findings

Skyrmions have an average diameter of 3 nm.

Skyrmions are localized within SrIrO3 regions, not the underlying SrRuO3.

Skyrmions are observed on islands of varying thickness without loss of contrast.

Abstract

Spin-polarized scanning tunneling microscopy (SPSTM) was used to directly image nanoscale N\'eel skyrmions in a SrIrO3 / SrRuO3 bilayer system that are among the smallest reported to date in any system. Off-axis magnetron sputtering was used to cap epitaxial films of the oxide ferromagnet SRO with 2 unit cells of SrIrO3, intended to provide interfacial spin orbit coupling. Atomic resolution STM imaging and tunneling spectroscopy were used to identify island-like SrIrO3 grains and small regions of bare SrRuO3. Isolated skyrmions were only observed in SrIrO3-covered regions of the film, and exhibited a distribution of sizes and shapes with an average diameter of 3 nm. We found that skyrmions must be fully contained within, but may be smaller than, any given SrIrO3 region. Additionally, skyrmions were observed on SrIrO3 islands of varying thickness without loss of SPSTM contrast, suggesting the magnetic texture lies within the SrIrO3 island rather than the underlying ferromagnetic SrRuO3. Density functional theory calculations suggest this could be due to a small induced magnetic moment associated with IrO layers in the SrIrO3 film.