Controlling adatom magnetism on bilayer graphene by external field

Employing first-principles calculations, we study the effect of an external electric field on the magnetic properties of a single Fe adatom and a Fe dimer hosted on a bilayer graphene surface grown on a ${\mathrm{SiO}}₂$ substrate. We find that an electric field perpendicular to the bilayer graphene modulates the charge and spin state of the single Fe adatom over a wide range. States ranging from $3{d}⁶,S=2$ to $3{d}¹⁰,S=0$ have been observed for the Fe adatom, which are inaccessible under normal conditions. This would be of interest in the context of the orbitally controlled Kondo effect. Further, for a Fe dimer, we find that a small electric field is able to tune the magnetic exchange coupling. Interestingly, we also observe an unusual magnetostructural coupling for the Fe dimer, which stabilizes a ferrimagnetic state over a fully compensated antiferromagnetic spin configuration.