Tuning the magnetic coupling of a molecular spin interface via electron doping

Mastering the magnetic response of molecular spin interfaces by tuning the occupancy of the molecular orbitals, which carry the spin magnetic moment, can be accomplished by electron doping. We propose a viable route to control the magnetization direction and magnitude of a molecular spin network, in a graphene-mediated architecture, achieved via alkali doping of manganese phthalocyanine (MnPc) molecules assembled on cobalt intercalated under a graphene membrane. The antiparallel magnetic alignment of the MnPc molecules with the underlying Co layer can be switched to a ferromagnetic state by electron doping. Multiplet calculations unveil an enhanced magnetic state of the Mn centers with a 3/2 to 5/2 spin transition induced by alkali doping, as confirmed by the steepening of the hysteresis loops, with higher saturation magnetization values. This new molecular spin configuration can be aligned by an external field, almost independently from the hard-magnet substrate effectively behaving as a free magnetic layer.