Evidence for high-temperature ferromagnetism in photolyzed ${\mathrm{C}}_{60}$

${\mathrm{C}}_{60}$ transforms to a polymeric phase where the ${\mathrm{C}}_{60}$ 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 ${\mathrm{C}}_{60}$ 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 $g=\mathrm{2.000.}\mathrm{}$ 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 ${\mathrm{C}}_{60}$ 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.