Molecular spin-probe sensing of H-mediated changes in Co nanomagnets.

The influence of hydrogen on magnetization is of substantial interest to spintronics. Understanding and controlling this phenomenon at the atomic scale, in particular in nanoscale systems, is crucial. In this study, we used scanning tunneling microscopy (STM) combined with a nickelocene molecule to sense the spin of a hydrogen-loaded nanoscale Co island grown on Cu(111). Magnetic exchange maps obtained from the molecular tip revealed the presence of a hydrogen superstructure and a 90° rotation of the magnetization compared to the pristine island. Ab initio calculations corroborate these observations, indicating that hydrogen hybridization with Co atoms on the island surface drives the spin reorientation of the island. This reorientation is further reinforced by hydrogen penetration into the island that locates at the Co/Cu interface. However, the subsurface sensitivity of the magnetic exchange maps indicates that this effect is limited. Our study provides valuable microscopic insights into the chemical control of magnetism at the nanoscale.