Antiferromagnetic order of topological orbital moments in atomic-scale skyrmion lattices

Due to electron motion in the emergent magnetic field of non-coplanar spin structures, topological orbital moments can arise even in the absence of spin-orbit coupling [1]. For atomic-scale skyrmion lattices [2], a significant effect can be expected, however, no studies have been reported yet. Here, we observe via spin-polarized scanning tunneling microscopy (SP-STM) a non-coplanar atomic-scale spin structure with a roughly square magnetic unit cell for a pseudomorphic Fe monolayer on three atomic Ir layers on Re(0001) [3,4]. Using density functional theory (DFT) we consider different skyrmion lattices as potential magnetic ground states [4]. Comparison of simulated and experimental SP-STM images provides strong evidence for an atomic-scale skyrmion lattice. By mapping the DFT results to an atomistic spin model we show that these spin textures are stabilized by the interplay of the Dzyaloshinskii-Moriya and four-spin interactions. We evaluate the emerging phenomena of the different non-coplanar magnetic states and find significant local topological orbital moments oriented perpendicular to the surface which order antiferromagnetically.

[1] S. Grytsiuk et al., Nat. Comm. 11, 511 (2020).

[2] S. Heinze et al., Nat. Phys. 7, 713 (2011).

[3] A. Kubetzka et al. Phys. Rev. Mat. 4, 081401 (2020)

[4] F. Nickel et al., arxiv: 2405.18088 (2024).