Kondo peak splitting on a single adatom coupled to a magnetic cluster

The Kondo resonance induced by a single cobalt adatom interacting with a ferromagnetic iron nanocluster is measured using low-temperature scanning tunneling microscopy. The persistence of the Kondo resonance is evidenced along with the predicted splitting of the spectral density peak for a Kondo impurity surrounded by a spin-polarized electron bath. Reversible quenching of the split feature is observed using atom manipulation between adjacent adsorption sites. Using a Green's-function formalism, we model a double Fano resonance leading to a quantitative insight of our observations.