title: Chiral magnetic order at surfaces driven by inversion asymmetry.
abstract: Chirality is a fascinating phenomenon that can manifest itself in subtle ways, for example in biochemistry (in the observed single-handedness of biomolecules) and in particle physics (in the charge-parity violation of electroweak interactions). 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. 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 occur. 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, causing a variety of excitations or manipulations of the magnetization and giving rise to microwave emission, magnetization switching, or magnetic motors.
authors.affiliation: Institute of Applied Physics and Microstructure Research Center, University of Hamburg, Jungiusstrasse 11, 20355 Hamburg, Germany. mbode@anl.gov
authors.forename: M
authors.initials: M
authors.lastname: Bode
authors.forename: M
authors.initials: M
authors.lastname: Heide
authors.forename: K
authors.initials: K
authors.lastname: von Bergmann
authors.forename: P
authors.initials: P
authors.lastname: Ferriani
authors.forename: S
authors.initials: S
authors.lastname: Heinze
authors.forename: G
authors.initials: G
authors.lastname: Bihlmayer
authors.forename: A
authors.initials: A
authors.lastname: Kubetzka
authors.forename: O
authors.initials: O
authors.lastname: Pietzsch
authors.forename: S
authors.initials: S
authors.lastname: Blügel
authors.forename: R
authors.initials: R
authors.lastname: Wiesendanger