  Magnetic skyrmions are localized nanometer-sized spin configurations with
particle_like properties, which are envisioned to be used as bits in
next_generation information technology. An essential step towards future
skyrmion-based applications is to engineer key magnetic parameters for
developing and stabilizing individual magnetic skyrmions. Here we demonstrate
the tuning of the non_collinear magnetic state of an Fe double layer on an
Ir111 substrate by loading the sample with atomic hydrogen. By using
spin_polarized scanning tunneling microscopy, we discover that the hydrogenated
system supports the formation of skyrmions in external magnetic fields, while
the pristine Fe double layer does not. Based on ab initio calculations, we
attribute this effect to the tuning of the Heisenberg exchange and the
Dzyaloshinsky_Moriya interactions due to hydrogenation. In addition to
interface engineering, hydrogenation of thin magnetic films offers a unique
pathway to design and optimize the skyrmionic states in low_dimensional
magnetic materials.
