The role of rare-earth atoms in the anisotropy and antiferromagnetic exchange coupling at a hybrid metal-organic interface

Magnetic anisotropy and magnetic exchange interactions are crucial parameters that characterize the hybrid metal-organic interface, key component of an organic spintronic device. We show that the incorporation of 4f RE atoms to hybrid metal-organic interfaces of CuPc/REAu_2 type (RE= Gd, Ho) constitutes a feasible approach towards on-demand magnetic properties and functionalities. The GdAu_2 and HoAu_2 substrates differ in their magnetic anisotropy behavior. Remarkably, the HoAu_2 surface boosts the inherent out-of-plane anisotropy of CuPc, owing to the match between the anisotropy axis of substrate and molecule. Furthermore, the presence of RE atoms leads to a spontaneous antiferromagnetic (AFM) exchange coupling at the interface, induced by the 3d-4f superexchange interaction between the unpaired 3d electron of CuPc and the 4f electrons of the RE atoms. We show that 4f RE atoms with unquenched quantum orbital momentum (L), as it is the case of Ho, induce an anisotropic interfacial exchange coupling.