Ferromagnetism in a cobaltocene-doped fullerene derivative below 19 K due to unpaired spins only on fullerene molecules

We report the discovery and physical properties of a new organic ferromagnet, 3-aminophenyl-methano-fullerene[60]-cobaltocene, with a Curie temperature TC of 19 K. Near- and mid-infrared spectroscopy together with electron spin resonance experiments show that spins reside entirely on the fullerene units, from which we deduce that the ferromagnetism is a consequence solely of exchange interactions between distributed p-electrons on the 3-aminophenyl-methano-fullerene[60] molecules. The ferromagnetic state of the compound is characterized by a very rapid transition to ferromagnetic order below TC, a low saturation field of Hs=40 Oe and no measurable hysteresis.