Structural\nManipulation of Spin Excitations in a Molecular\nJunction

Single metallocene molecules act as sensitive spin detectors\nwhen\ndecorating the probe of a scanning tunneling microscope (STM). However,\nthe impact of the atomic-scale electrode details on the molecular\nspin state has remained elusive to date. Here, a nickelocene (Nc)\nSTM junction is manipulated in an atomwise manner showing clearly\nthe dependence of the spin excitation spectrum on the anchoring of\nNc to Cu(111), a Cu monomer, and trimer. Moreover, while the spin\nstate of the same Nc tip is a triplet with tunable spin excitation\nenergies upon contacting the surface, it transitions to a Kondo-screened\ndoublet on a Cu atom. Notably, the nontrivial magnetic exchange interaction\nof the molecular spin with the electron continuum of the substrate\ndetermines the spectral line shape of the spin excitations.