Magnetism of C-60 induced by photo-assisted oxidation

The C-60 crystals which are exposed to light in oxygen show a ferromagnetic magnetization with a small hysteresis of the coercive field H-c = 10(-2) T and a saturation magnetic moment (Ms) of 10(-3) mu(B) per C-60. The most striking feature is that Ms remains up to Tc = 800 K, an extraordinarily high critical temperature. The small Ms indicates that only a small part of the sample contributes to the ferromagnetism, but the ferromagnetic part can be enriched by dissolution of pure C-60 into toluene; a residue substance has a larger Ms of 10(-1) mu B/C-60. The x-ray powder diffraction and the Raman scattering measurements reveal that the residue has a crystal structure close to pure C-60 crystal although a broadening of line width in the diffraction spectrum and a small shift of Ag and Hg vibrational modes to a lower energy are observed. The mechanism of the ferromagnetism will be discussed in relation to oxidization and polymerization of C-60 molecules.