Interplay between antiferromagnetic and ferromagnetic phases of TDAE-${\mathrm{C}}_{60}$: An ESR study of high-temperature annealed samples

The low-temperature magnetic properties of annealed TDAE-${\mathrm{C}}_{60}$ single crystals are studied with electron spin resonance. Whereas freshly grown single crystals are found to order antiferromagnetically at low temperature, annealing at room temperature and above results in an enhanced ferromagnetic ordering and three separate magnetic phases can be identified below 25 K, below 16 K, and below 10 K. The orientational ordering transition temperature $T_0$ is found to be correlated with the annealing temperature $T_a$ and the drop in susceptibility which is systematically observed below 100 K is interpreted as the onset of antiferromagnetic correlations.