  The ability to electrically-drive spin excitations in molecules with magnetic
anisotropy is key for high-density storage and quantum-information technology.
Electrons, however, also tunnel via the vibrational excitations unique to a
molecule. The interplay of spin and vibrational excitations offers novel routes
to study and, ultimately, electrically manipulate molecular magnetism. Here we
use a scanning tunneling microscope to electrically induce spin and vibrational
excitations in a single molecule consisting of a nickelocene magnetically
coupled to a Ni atom. We evidence a vibron-assisted spin excitation at an
energy one order of magnitude higher compared to the usual spin excitations of
nickelocene and explain it using first-principles calculations that include
electron correlations. Furthermore, we observe that spin excitations can be
quenched by modifying the Ni-nickelocene coupling. Our study suggests that
nickelocene-based complexes constitute a model playground for exploring the
interaction of spin and vibrations in the electron transport through single
magnetic molecules.
