Hydrogen toggling between Yoshimori spin spirals and elliptical Dzyaloshinskii-Moriya skyrmions in Fe on Ir(110)

Abstract: Skyrmions are particle-like spin textures that arise from spin spiral states in the presence of an external magnetic field. These spirals can originate from either frustrated Heisenberg exchange interactions or the interplay between exchange interactions and the relativistic Dzyaloshinskii-Moriya interaction, leading to atomic- and mesoscale textures, respectively. However, the conversion of exchange-stabilized spin spirals into skyrmions typically requires magnetic fields that exceed practical laboratory limits. Here, we demonstrate a strategy leveraging hydrogen adsorption to expand the range of magnetic films capable of hosting stable or metastable skyrmions. In a structurally open and anisotropic system of two pseudomorphic Fe layers on Ir(110), spin-polarized scanning tunneling microscopy combined with ab initio calculations reveals that a right-handed, exchange-stabilized N\'eel-type spin spiral propagating along the [$\overline{1}10$] direction with a $1.3$~nm period transitions upon hydrogen adsorption to a Dzyaloshinskii-Moriya type spiral with a sevenfold longer period of $8.5$~nm. This transition enables elliptical skyrmions to form at moderate magnetic fields. Hydrogenation thus provides a non-volatile mechanism to toggle between distinct magnetic states, offering a versatile platform for controlling spin textures.