Annealing effects on the magnetic and structural properties of single-crystalTDAE−C60

Annealing effects on the magnetic and structural properties of single-crystal TDAE-${\mathrm{C}}_{60}$ are investigated. When a crystal is well-annealed at 350 K, ferromagnetic ordering takes place below 16 K, though no magnetic phase transition is shown in as-grown crystal. The saturated magnetization was obtained to be $0.9\pm 0.1{\mu }_{\mathrm{B}}$ per ${\mathrm{C}}_{60}.$ It was first found that the well-annealed crystal shows a structural phase transition around 180 K, probably associated with the orientational ordering of ${\mathrm{C}}_{60}$ molecules. On the other hand, the as-grown crystal undergoes no structural phase transition at least down to 30 K while the motion of ${\mathrm{C}}_{60}$ molecules is restricted below around 150 K. The possible relation between the low-temperature structure and the magnetic ordering is discussed.