Independent excitations of the spin and orbital momenta in a single magnetic atom

R. Rejali, D. Coffey, J. Gobeil, J. W. González, F. Delgado, A. F. Otte

Published 2019-10-01Version 1

We use spin-polarized inelastic tunneling spectroscopy to probe the magnetic properties of single Fe atoms bound to the nitrogen sites of Cu$_2$N. We report a zero-field splitting of $18.4 \pm 0.1$ meV---the largest reported for Fe adatoms on surfaces---which arises from a largely preserved orbital angular momentum. In addition to two distinct inelastic spin excitations, we observe an excitation of the orbital moment, which we describe in terms of a cotunneling mechanism. We explain these observations using density functional theory and multiplet calculations, accounting for the unquenched, anisotropic orbital moment.