Magnetic properties of crystals of the molecular complex between fullerene C60 and an organic donor 9,9′-trans-bis(telluraxanthenyl)

The EPR and static magnetic susceptibility of the crystalline molecular complex between fullerene C60 and an organic donor 9,9′-trans-bis(telluraxanthenyl) (BTX) have been measured as functions of temperature. At temperatures T above 130 K, the samples exhibit anomalously high magnetic susceptibility exceeding the values calculated under the assumption that each molecule bears one paramagnetic spin 1/2. A very intense magnetic resonance signal is also observed in the samples in the region of high g factors (g>4.5). This allows the suggestion that the samples under study possess ferromagnetism (or superparamagnetism). The EPR signal and magnetic susceptibility sharply decay almost to zero as the temperature decreases below 100–120 K. It is supposed that electron transfer from donor molecules BTX to C60 molecules takes place at temperatures above 110 K. This electron transfer generates electron spins in the system, whereas the anomalously high magnetism is due to ferromagnetic correlations in the system of these spins.