1. Institute of Applied Physics and Microstructure Research Center, University of Hamburg, Jungiusstrasse 11, 20355 Hamburg, Germany
2. Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich, Germany
3. Present address: Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, USA.

Correspondence to: M. Bode^1,3 Correspondence and requests for materials should be addressed to M.B. (Email: mbode@anl.gov).

Abstract

Chirality is a fascinating phenomenon that can manifest itself in subtle ways, for example in biochemistry (in the observed single-handedness of biomolecules¹) and in particle physics (in the charge-parity violation of electroweak interactions²). In condensed matter, magnetic materials can also display single-handed, or homochiral, spin structures. This may be caused by the Dzyaloshinskii–Moriya interaction, which arises from spin–orbit scattering of electrons in an inversion-asymmetric crystal field^{3, 4}. This effect is typically irrelevant in bulk metals as their crystals are inversion symmetric. However, low-dimensional systems lack structural inversion symmetry, so that homochiral spin structures may occur⁵. Here we report the observation of magnetic order of a specific chirality in a single atomic layer of manganese on a tungsten (110) substrate. Spin-polarized scanning tunnelling microscopy reveals that adjacent spins are not perfectly antiferromagnetic but slightly canted, resulting in a spin spiral structure with a period of about 12 nm. We show by quantitative theory that this chiral order is caused by the Dzyaloshinskii–Moriya interaction and leads to a left-rotating spin cycloid. Our findings confirm the significance of this interaction for magnets in reduced dimensions. Chirality in nanoscale magnets may play a crucial role in spintronic devices, where the spin rather than the charge of an electron is used for data transmission and manipulation. For instance, a spin-polarized current flowing through chiral magnetic structures will exert a spin-torque on the magnetic structure^{6, 7}, causing a variety of excitations or manipulations of the magnetization^{8, 9} and giving rise to microwave emission, magnetization switching, or magnetic motors.

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