Room temperature magnetism of ordered porphyrin layers on Fe

We propose a method to grow metal tetraphenyl porphyrin (MTPP) molecular layers where a long-range structural and magnetic order can be achieved simultaneously and at room temperature by a proper treatment of the ferromagnetic substrate. We focus in particular on the oxygen-passivated Fe(001)-p(1 × 1)O surface, where MTPP molecules (with M=Co and Ni) arrange by forming square commensurate overlayers. Spin-resolved photoemission detects a clear spin-splitting of CoTPP electronic states, while no magnetic response is obtained from NiTPP, as expected from the electronic configuration of the respective free molecules. We link these observations to the decoupling action of oxygen at the interface, whose effect is to enhance the molecular diffusivity and tune the electronic interaction with the substrate electronic structure.