A theoretical study of the dynamical switching of a single spin by exchange forces

We demonstrate the possibility of dynamically switching the spin of a single atom or molecule with the magnetic tip of an atomic force microscope making use of the acting exchange forces. We choose single V-, Nb- and Ta-benzene molecules as model systems and calculate the exchange interaction with an Fe tip using density functional theory. The exchange energy displays a Bethe–Slater-type behavior with ferromagnetic coupling at large tip–sample distance and antiferromagnetic coupling at closer proximity. The exchange energies reach maximum values of a few tens of meV, which allows one to switch single spins by overcoming the energy barrier due to the magneto-crystalline anisotropy. The spin dynamics of the system was explored by solving the time-dependent Schrödinger equation with additional Landau–Lifshitz-like spin relaxation. We find that the distance dependence of the exchange interaction as well as the appearance of quantum tunneling results in different scenarios for the switching behavior, e.g. the tip can switch the adatom or lead to a stable superposition state with zero magnetization. (paper)