Field-regulated switching of the magnetization of Co-porphyrin on graphene

Different magnetic coupling mechanisms have been identified for a few monolayers of Co-porphyrin molecules deposited on a graphene-covered Ni(111) single crystal. A relatively strong antiferromagnetic coupling of the first molecular layer via graphene to the Ni crystal in comparison to a weaker intermolecular coupling gives rise to a complex field-dependent response of this hybrid system. By continuously increasing the magnetic field strength, the net magnetization of the molecular system switches from antiparallel to parallel to the field direction at 2.5 T. Utilizing x-ray absorption spectroscopy and x-ray magnetic circular dichroism, the element-specific magnetization and field dependence was probed. The nature of the magnetic couplings is identified by means of density functional theory and orbital-dependent susceptibilities. © 2014 American Physical Society.