How to measure the local Dzyaloshinskii Moriya Interaction in Skyrmion Thin Film Multilayers

TL;DR

This paper investigates local Dzyaloshinskii Moriya interactions in skyrmion-hosting thin film multilayers, revealing how inhomogeneities and layer flatness influence skyrmion size, shape, and pinning, with implications for spintronic applications.

Contribution

It introduces a method to measure local DM interactions in thin films and demonstrates the impact of layer inhomogeneity on skyrmion behavior at room temperature.

Findings

Skyrmions smaller than previously observed in multilayers.

Skyrmions are not circularly symmetric and are pinned to specific areas.

Layer thickness inhomogeneity correlates with skyrmion pinning.

Abstract

The current driven motion of skyrmions in MnSi and FeGe thinned single crystals could be initiated at current densities of the order of $10^6$ A/m, five orders of magnitude smaller than for magnetic domain walls. The technologically crucial step of replicating these results in thin films has not been successful to date, but the reasons are not clear. Elucidating them requires analyzing system characteristics at scales of few nm where the key Dzyaloshinskii Moriya (DM) interactions vary, and doing so in near application conditions, i.e. oxidation protected systems at room temperature. In this work's magnetic force microscopy (MFM) studies of magnetron sputtered Ir/Co/Pt multilayers we show skyrmions that are smaller than previously observed, are not circularly symmetric, and are pinned to 50 nm wide areas of 75 percent higher than average DM interaction. This finding matches our measurement of Co layer thickness inhomogeneity of the order of $\pm$1.2 atomic monolayers per 0.6 nm layer, and indicates that layer flatness must be controlled with greater precision to preclude skyrmion pinning.