Magnetic coupling of porphyrin molecules through graphene.

X-ray magnetic circular dichroism (XMCD) measurements and density functional theory (DFT)+U calculations reveal an unexpected antiferromagnetic coupling between physisorbed paramagnetic Co-porphyrin molecules and a Ni surface, separated by a graphene layer. A positive magnetization at the Ni substrate atoms is mediated by graphene and induces a negative one at the Co site, despite only a very small overlap between macrocyclic π and graphene pz -orbitals.