  Magnetic molecules deposited on surfaces are a promising platform to
individually address and manipulate spins. Long spin excitation lifetimes are
necessary to utilize them in quantum information processing and data storage.
Normally, coupling of the molecular spin with the conduction electrons of
metallic surfaces causes fast relaxation of spin excitations into the ground
state. However, the presence of superconducting paring effects in the substrate
can protect the excited spin from decaying. In this work, we show that a
proximity-induced superconducting gold film can sustain spin excitations of a
FeTPP-Cl molecule for more than 80ns. This long value was determined by
studying inelastic spin excitations of the S=5/2 multiplet of FeTPP-Cl on Au
films over V(100) using scanning tunneling spectroscopy. The spin lifetime
decreases with increasing film thickness, in apparent connection with the
gradual gap-closing of a pair of de Gennes-Saint James resonances found inside
the superconducting gap. Our results elucidate the use of proximitized gold
electrodes for addressing quantum spins on surfaces, envisioning new routes for
tuning the value of their spin lifetime.
