Ferromagnetism in stacked bilayers of Pd/C60

• Ferromagnetism with a high Curie temperature (>500K) is observed in stacked bilayers of Pd/C60.
• The Pd and C60 layers were sequentially grown using dc sputtering of Pd and thermal sublimation of C60.
• Spectroscopic and electron microscopy measurements confirm the layered structure.
• Density functional theory (DFT) calculations show that the Pd/C60 interaction provides a good description of the observed ferromagnetism.
• Although ferromagnetism in nanostructured Pd is known, Pd/C60 composites (bilayers) offer an additional mechanism for ferromagnetism not previously considered.

We provide experimental evidence for the existence of ferromagnetism in bilayers of Pd/C60 which is supported by theoretical calculations based on density functional theory (DFT). The observed ferromagnetism is surprising as C60 and Pd films are both non-ferromagnetic in the non-interacting limit. Magnetization (M) versus applied field (H) data acquired at different temperatures (T) show magnetic hysteresis with typical coercive fields (Hc) on the order of 50 Oe. From the temperature-dependent magnetization M(T  ) we extract a Curie temperature (TC≥550K) using Bloch-like power law extrapolations to high temperatures. Using DFT calculations we investigated all plausible scenarios for the interaction between the C60 molecules and the Pd slabs, Pd single atoms and Pd clusters. DFT shows that while the C60 molecules are nonmagnetic, Pd films have a degenerate ground state that, subject to a weak perturbation, can become ferromagnetic. Calculations also show that the interaction of C60 molecules with excess Pd atoms and with sharp edges of a Pd slab is the most likely configuration that render the system ferromagnetic. Interestingly, the calculated charge transfer (0.016 e per surface Pd atom, 0.064 e per Pd for intimate contact region) between C60 and Pd does not appear to play an important role.