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 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 field3,4. 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 structure6,7, causing a variety of excitations or manipulations of the magnetization8,9 and giving rise to microwave emission, magnetization switching, or magnetic motors.

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Figure 1: Antiferromagnetic (AFM) structure of a Mn monolayer on W(110).
Figure 2: SP-STM of the Mn monolayer on W(110) and potential spin structures.
Figure 3: Field-dependent SP-STM measurements.
Figure 4: Calculated energy of homogeneous cycloidal spin spirals.

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Acknowledgements

Financial support from the project ‘spin–orbit effects in magnetic systems’ and the Sonderforschungsbereich “Magnetismus vom Einzelatom zur Nanostruktur” of the Deutsche Forschungsgemeinschaft, from the Stifterverband für die Deutsche Wissenschaft, and from the Interdisciplinary Nanoscience Center Hamburg is gratefully acknowledged.

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Correspondence to M. Bode.

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Bode, M., Heide, M., von Bergmann, K. et al. Chiral magnetic order at surfaces driven by inversion asymmetry. Nature 447, 190–193 (2007). https://doi.org/10.1038/nature05802

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