Temperature induced de-polymerization in TDAE-C₆₀

The phase change due to the polymerization of the ferromagnetic tetrakis-dimethylamino-ethylene (TDAE)-C₆₀ has been reconfirmed by applying pressures in situ up to P_c = 7 kbar in an ESR cavity. This transition is irreversible and the phase above P_c is stable even after releasing pressure. The pressure-dependent g-factor indicates the revival of the TDAE⁺ spins. Moreover, the ferromagnetism disappears simultaneously at P_c. The de-polymerization of the polymerized (pressure-released) crystal has been confirmed for the first time by the high-temperature ESR study. This transition is also irreversible and the polymer phase is stable up to 470 K. The de-polymerized phase is considered to be the original ferromagnetic one.