Indirect Chiral Magnetic Exchange through Dzyaloshinskii-Moriya–Enhanced RKKY Interactions

Localized electron spins can couple magnetically via the Ruderman-Kittel-Kasuya-Yosida interaction even if their wave functions lack direct overlap. Theory predicts that spin-orbit scattering leads to a Dzyaloshinskii-Moriya type enhancement of this indirect exchange interaction, giving rise to chiral exchange terms. Here we present a spin-polarized scanning tunneling microscopy study of transition metal oxide chains on the (001) surfaces of Ir and Pt. Our STM results confirm that deposition of Co, Fe, Mn, and Cr on the (2×1) oxygen-reconstructed Ir(001) surface leads to the formation of quasi-one-dimensional chains with a (3×1) unit cell. In contrast, preparation on Pt(001) required deposition onto the cold substrate with subsequent annealing in an oxygen atmosphere. In particular, for MnO₂ chains we found highly complex spin structures. Whereas we find an almost antiferromagnetic Mn–Mn coupling along the chains, the inter-chain coupling across the non-magnetic substrates turns out to be chiral. We will show that some of the magnetic structures observed for MnO₂ can be viewed as highly anisotropic Skyrmions.