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.

Symmetry breaking in the formation of magnetic vortex states in a permalloy nanodisk

“…To interpret and explain the asymmetric process of VS formation, we took the DMI into consideration, because it inevitably arises from the spin-orbital coupling due to the broken inversion symmetry at surfaces/interfaces in magnetic thin layers 17,18 . The DMI has been discussed as the origin for spin spiral textures and has been theoretically predicted to affect the shape and size of magnetic vortices 20,21 .…”

“…where D is the Dzyaloshinskii constant, which determines the magnitude of the DMI and its sign specifies the orientation of spin spiral state owing to the DMI 18,20 . For this simulation, we adapted a three-dimensional (3D) model where the DMI exists only on the disk surfaces (top, bottom and lateral) because the DMI is considered to be localized at the surface 18,[22][23][24] .…”

“…For this simulation, we adapted a three-dimensional (3D) model where the DMI exists only on the disk surfaces (top, bottom and lateral) because the DMI is considered to be localized at the surface 18,[22][23][24] . A schematic diagram of the 3D modelling is shown in Fig.…”

“…The origin of the experimentally observed asymmetric phenomenon is interpreted as the combination of an 'intrinsic' Dzyaloshinskii-Moriya interaction (DMI) arising from the spin-orbit coupling 17,18 and surface-related 'extrinsic' factors, such as edge defects, surface roughness, and so on. We utilize full-field magnetic transmission soft X-ray microscopy (MTXM) with high-spatial resolution down to 20 nm (ref.…”

Structurally driven magnetic state transition of biatomic Fe chains on Ir(001)

“…The manipulation of exchange interactions opens another path to create new materials with a magnetic state that may be tunable by external magnetic or electric fields. 4 E.g., the occurrence of chiral spin spiral states at surfaces has been demonstrated, 5,6 their manipulation by electrical currents was suggested 5,7 and a way to grow films with multiple metastable magnetic states has been proposed. 8 The ability to create one-dimensional ͑1D͒ monoatomic magnetic chains of transition metals on surfaces by self-organization 9,10 or by manipulation with a scanning tunneling microscope 11 has recently opened new vistas to explore and manipulate artificial magnetic nanostructures even atom by atom.…”