An Orbitally-Derived Single Atom Magnetic Memory

Single atoms at the surfaces of solids have demonstrated rich electronic, chemical, and magnetic properties. In this direction, we show that we can manipulate the valency of a single cobalt atom on a crystalline black phosphorus surface. Using the local electric field generated from an STM tip, individual cobalt atoms residing at the same hollow site can be reversibly switched between two stable states, which correspond to the different valencies. Consistency between experimentally observed charge densities and density functional theory calculations reveal distinct high and low total magnetic moments for each state. We investigate the stability of each configuration, as well as compare the experimentally measured impurity states with DFT calculations. Finally, we probe the switching dynamics to determine the underlying mechanism and energy scale of the switching. This system opens up the horizon to explore complex memory based on both the orbital and spin degrees of freedom.