Ferromagnetism in stacked bilayers of Pd/C sub(60)

• Published in: Journal of magnetism and magnetic materials Vol. 349; pp. 128 - 134
• Main Authors: Ghosh, S, Tongay, S, Hebard, A F, Sahin, H, Peeters, F M
• Format: Journal Article
• Language: English
• Published: 01.01.2014
• Subjects: Buckminsterfullerene; Coercive force; Ferromagnetism; Fullerenes; Magnetization; Mathematical analysis; Palladium; Slabs
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2013.07.024

We provide experimental evidence for the existence of ferromagnetism in bilayers of Pd/C sub(60) which is supported by theoretical calculations based on density functional theory (DFT). The observed ferromagnetism is surprising as C sub(60) 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 (H sub(c)) on the order of 50 Oe. From the temperature-dependent magnetization M (T ) we extract a Curie temperature (TC greater than or equal to 550K) using Bloch-like power law extrapolations to high temperatures. Using DFT calculations we investigated all plausible scenarios for the interaction between the C sub(60) molecules and the Pd slabs, Pd single atoms and Pd clusters. DFT shows that while the C sub(60) 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 C sub(60) 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 C sub(60) and Pd does not appear to play an important role.