Measuring the Dzyaloshinskii-Moriya interaction of the epitaxial Co/Ir(111) interface

TL;DR

This study measures the Dzyaloshinskii-Moriya interaction at the epitaxial Co/Ir(111) interface using in situ microscopy, revealing how magnetic domain wall structures vary with cobalt thickness and quantifying the interfacial DMI strength.

Contribution

It provides the first experimental quantification of the DMI at the epitaxial Co/Ir(111) interface with atomically flat growth, linking domain wall structure to DMI strength.

Findings

Pure Néel walls below 8.8 ML cobalt thickness

Transition to mixed Bloch-Néel domain walls at larger thicknesses

Interfacial DMI parameter D_s = -1.07 pJ/m

Abstract

The in-plane orientation of the magnetization in the center of domain walls is measured in Co/Ir(111) as a function of Co thickness via scanning electron microscopy with polarization analysis. Uncapped, thermally evaporated cobalt on an Ir(111) single-crystal surface is imaged in situ in ultra-high vacuum. The initial pseudomorphic growth with an atomically flat interface of cobalt on iridium ensures comparability to theoretical calculations and provides a study of an interface that is as ideal as possible. Below a cobalt thickness of 8.8 monolayers, the magnetic domain walls are purely N\'eel oriented and show a clockwise sense of rotation. For larger thicknesses the plane of rotation changes and the domain walls show a significant Bloch-like contribution, allowing to calculate the strength of the Dzyaloshinskii-Moriya interaction (DMI) from energy minimization. From the angle between the plane of rotation and the domain-wall normal an interfacial DMI parameter $D_s = -(1.07 \pm 0.05)$ pJ/m is determined, which corresponds to a DMI energy per bond between two Co atoms at the interface of $d_{tot} = -(1.04 \pm 0.05)$ meV.