Reversible Manipulation of the Magnetic Coupling of Single Molecular Spins in Fe-Porphyrins to a Ferromagnetic Substrate

We demonstrate by means of X-ray magnetic circular dichroism that the magnetization of paramagnetic Fe-octaethylporphyrin (FeOEP) molecules coupled antiferromagnetically to an oxygen-covered Co ultrathin film grown on Cu(001) can be reduced by about 50% by the adsorption of nitrogen monoxide (NO). From the similarity of Fe X-ray absorption spectra before and after NO adsorption, we conclude that this effect is the result of a reduction of the magnetic superexchange coupling between the Fe ions and the substrate caused by physisorbed NO molecules, leading to the reduced molecular magnetization. After thermal desorption of the NO from the Fe ion, the original FeOEP magnetization is restored. The reversibility of the process is proven by successfully repeating the NO dosing-desorbing procedure.