INTERPLAY BETWEEN ANTIFERROMAGNETIC AND FERROMAGNETIC PHASES OF TDAE-C-60 - AN ESR STUDY OF HIGH-TEMPERATURE ANNEALED SAMPLES

The low-temperature magnetic properties of annealed TDAE-C-60 single c rystals are studied with electron spin resonance. Whereas freshly grow n single crystals are found to order antiferromagnetically at low temp erature, annealing at room temperature and above results in an enhance d ferromagnetic ordering and three separate magnetic phases can be ide ntified below 25 K, below 16 K, and below 10 K. The orientational orde ring transition temperature T-0 is found to be correlated with the ann ealing temperature T-a and the drop in susceptibility which is systema tically observed below 100 K is interpreted as the onset of antiferrom agnetic correlations.