  Quantum sensing is a key component of quantum technology, enabling highly
sensitive magnetometry. We combined a nickelocene molecule with scanning
tunneling microscopy to perform versatile spin sensing of magnetic surfaces,
namely of model Co islands on Cu(111) of different thickness. We demonstrate
that atomic-scale sensitivity to spin polarization and orientation is possible
due to direct exchange coupling between the Nc-tip and the Co surfaces. We find
that magnetic exchange maps lead to unique signatures, which are well described
by computed spin density maps. These advancements improve our ability to probe
magnetic properties at the atomic level.
