ANTIFERROMAGNETIC-TO-FERROMAGNETIC TRANSFORMATION IN POWDERED TDAE-C-60

Electron spin resonance measurements on powdered TDAE-C-60 demonstrate that freshly prepared samples show at first a transition to a low-tem perature ''antiferromagnetic'' like phase and that on annealing at roo m temperature they transform to the modification which exhibits a tran sition to the ferromagnetic ground state. The characteristic time for this transformation is in powdered samples only of several hours, whil e in single crystals it is of the order of several weeks. The above di fference could be due to the different strain distribution which affec ts the freedom of rotation of the C-60(-) ions and thus the exchange c oupling.