Helical spin order in Fe nanoislands

We report a spin-polarized scanning tunneling microscopy and spectroscopy (SP-STM/S), with an atomic scale resolution, of individual nanostructures of biatomic-layer-high Fe on Cu(111). SP-STM/S of the Fe nanoislands reveals a magnetic stripe phase with a period of 1.28 nm, which is identified as a one-dimensional helical spin order [1]. \textit{Ab initio} calculations identify reduced-dimensionality-enhanced long range antiferromagnetic interactions as the driving force of this spin order, whereas the contribution of the spin-orbit coupling is negligible. In addition, energy-resolved SP-STS mapping provide a spatially-resolved and spin-dependent electronic structure of this helical spin order. The wave vector describing the spin order remains constant in the energy range --0.8 to $+$0.6 eV, whereas the spin contrast shows dissipation features around and sign change across the Fermi energy. We discuss the results in view of an energy gap opening associated with the non-collinear spin order. Our result identifies a novel aspect of SP-STM/S to characterize complex spin order with respect to the corresponding spin-dependent electronic band structure. \\[4pt] [1] S. Phark et al., \textit{Nat}. \textit{Commun}. 5 DOI: 10.1038/ncomms6183 (2014).