  The Dzyaloshinskii-Moriya interaction (DMI) has drawn great attention as it
stabilizes magnetic chirality, with important implications in fundamental and
applied research. This antisymmetric exchange interaction is induced by the
broken inversion symmetry at interfaces or in non-centrosymmetric lattices.
Significant interfacial DMI was found often at magnetic / heavy-metal
interfaces with large spin-orbit coupling. Recent studies have shown promise of
induced DMI at interfaces involving light elements such as carbon (graphene) or
oxygen. Here we report direct observation of induced DMI by chemisorption of
the lightest element, hydrogen, on a ferromagnetic layer at room temperature,
which is supported by density functional theory calculations. We further
demonstrate a reversible chirality transition of the magnetic domain walls due
to the induced DMI via hydrogen chemisorption/desorption. These results shed
new light on the understanding of DMI in low atomic number materials and design
of novel chiral spintronics and magneto-ionic devices.
