Evidence for high-temperature ferromagnetism in photolyzed C₆₀

C₆₀ transforms to a polymeric phase where the C₆₀ molecules are bonded to form a chain structure when it is subjected to ultraviolet radiation at ambient temperature in the absence of oxygen. The electron paramagnetic resonance spectrum of C₆₀ photolyzed in the presence of a low pressure of oxygen or in air shows a very broad, asymmetric derivative signal at room temperature and at a magnetic field position well removed from g=2.000. With decreasing temperature, the broad line shifts to lower magnetic fields and increases further in linewidth, as expected for a ferromagnetic resonance signal. A low-field nonresonant derivative signal is also observed, consistent with the existence of ferromagnetism. Ferromagnetism up to room temperature in photolyzed C₆₀ is confirmed unequivocally by superconducting quantum interference device measurements of the dc magnetization as a function of magnetic field. A possible model for the origin of ferromagnetism based on these results and Raman data on photolyzed samples is also proposed.