Vector magnetic field characterization of individual atoms

Stability of magnets is determined by the magnetic anisotropy. Here we show first experiments with a scanning tunneling microscope operating in a three-axis vector magnet that can measure the full three-dimensional magnetic anisotropy field of individual atoms. We focus on Fe atoms on a copper nitride monolayer grown on copper. The evolution of spin excitations during magnetic field rotations directly resolves the symmetry class of the magnetic anisotropy. These experiments demonstrate the feasibility of mapping the vector-properties of spins and future exploration of complex three-dimensional magnetic systems.