Spin Spiral State at a Ferromagnetic Gd Vacuum Interface

Abstract: Centrosymmetric bulk magnets made of layered Gd intermetallics had been discovered recently to exhibit helical spin spirals with a wavelength of ≈2 nm that transform into skyrmion lattices at certain magnetic fields. Here we report on the observation of a spin spiral state at the Gd(0001) surface. Spinpolarized scanning tunneling microscopy images show striped regions with a periodicity of about 2 nm. These stripes rearrange upon application of an external magnetic field, thereby unambiguously confirming their magnetic origin. Density functional theory calculations explain that competing exchange interactions in the surface layer of Gd(0001) together with a magnetovolume fine-tuning of the exchange interaction to the next Gd layer favor a chiral 2 nm conical spin spiral at the surface, arising as a general behavior of the Gd monolayer. Other: Please read the "README.txt" file for further information. Other: We acknowledge financial support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), S. B. through SFB 1238 Project No. 277146847 (project C01), M. B. through Project No. 510676484 (GZ: BO 1468/29-1), and under Germany’s Excellence Strategy through the Würzburg– Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter—ct.qmat (EXC 2147, Project No. 390858490). G. B. gratefully acknowledges computing time granted through JARA-HPC on the supercomputer JURECA at Forschungszentrum Jülich.