Antiferromagnetic coupling of TbPc₂ molecules to ultrathin Ni and Co films

The magnetic and electronic properties of single-molecule magnets are studied by X-ray absorption spectroscopy and X-ray magnetic circular dichroism. We study the magnetic coupling of ultrathin Co and Ni films that are epitaxially grown onto a Cu(100) substrate, to an in situ deposited submonolayer of TbPc₂ molecules. Because of the element specificity of the X-ray absorption spectroscopy we are able to individually determine the field dependence of the magnetization of the Tb ions and the Ni or Co film. On both substrates the TbPc₂ molecules couple antiferromagnetically to the ferromagnetic films, which is possibly due to a superexchange interaction via the phthalocyanine ligand that contacts the magnetic surface.