We show that, in graphene with a small concentration of adatoms, the total magnetic moment μT can be switched on and off by varying the Fermi energy EF, either by applying a gate voltage or by suitable chemical doping. Our calculation is carried out using a simple tight-binding model described previously, combined with a mean-field treatment of the electron-electron interaction on the adatom. The values of EF at which the moment is turned on or off are controlled by the strength of the hopping between the graphene sheet and the adatom, the on-site energy of the adatom, and the strength of the electron-electron correlation energy U. Our result is in qualitatively consistent with recent experiments by Nair {\it et al.} [Nat.\ Commun.\ {\bf 4}, 2010 (2013)].
@article{arxiv.1405.7634,
title = {Graphene with adatoms: tuning the magnetic moment with an applied voltage},
author = {N. A. Pike and D. Stroud},
journal= {arXiv preprint arXiv:1405.7634},
year = {2014}
}