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.

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).

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