We report photoemission experiments revealing the valence electron spectral function of Mn, Fe, Co, and Ni atoms on the Ag (100) surface. The series of spectra shows splittings of higher energy features which decrease with the filling of the $3d$ shell and a highly nonmonotonic evolution of spectral weight near the Fermi edge. First principles calculations demonstrate that two manifestations of Hund’s exchange $J$ are responsible for this evolution. First, there is a monotonic reduction of the effective exchange splittings with increasing filling of the $3d$ shell. Second, the amount of charge fluctuations and, thus, the weight of quasiparticle peaks at the Fermi level varies nonmonotonically through this $3d$ series due to a distinct occupancy dependence of effective charging energies $U_{\mathrm{eff}}$.

• Received 7 December 2012

DOI:https://doi.org/10.1103/PhysRevLett.110.186404