Existence of Ferromagnetism in Stacked Bilayers of Pd/C60

We report on an experimental and theoretical study of the magnetic properties of multilayer structures fabricated by alternating layers of sputter-deposited Pd and thermally-sublimated C$_{60}$. Auger Electron Spectroscopy and SEM techniques have been used to characterize samples for which magnetic measurements in a commercially available SQUID have been made. The magnetization measurement reveals ferromagnetism in the Pd/C$_{60}$ system, which has Curie temperature T$_{C} \quad \sim $ 450K, modified Bloch coefficient P $\sim $ 2.7 and a temperature-independent coercive field of 50 Oe. The observed ferromagnetism is surprising since both C$_{60}$ and Pd are non-ferromagnetic in the non-interacting limit. Density functional theory (DFT) calculations show that while the C$_{60}$ molecules are nonmagnetic unless polymerized, Pd films have a degenerate ground state that can become ferromagnetic with a weak perturbation. Though the calculated charge transfers of $\sim $0.06 e between C$_{60}$ and Pd are not the cause of ferromagnetism, DFT shows that ferromagnetism can be associated with Pd clusters or an interaction of C$_{60}$ molecules with sharp edges of the Pd thin film.