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

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 iridium single-crystal surface is imaged in situ in ultra-high vacuum. The 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. The angle between the plane of rotation and the domain-wall normal allows for calculating the interfacial DMI parameter $D_s = -(1.19 \pm 0.03)$ pJ/m which corresponds to a DMI energy per bond between two Co atoms at the interface of $d_{tot} = -(1.16 \pm 0.03)$ meV.