Critical exponents at the ferromagnetic transition in tetrakis(dimethylamino)ethylene-C60 (TDAE-C60)

Critical exponents at the ferromagnetic transition were measured for the first time in an organic ferromagnetic material tetrakis(dimethylamino)ethylene fullerene[60] (TDAE-C-60). From a complete magnetization-temperature-field data set near T-c = 16.1 +/- 0.05, we determine the susceptibility and magnetization critical exponents gamma = 1.22 +/- 0.02 and beta = 0.75 +/- 0.03, respectively, and the field vs magnetization exponent at T-c of delta = 2.28 +/- 0.14. Hyperscaling is found to be violated by Omega = d' - d approximate to 1/4, suggesting that the onset of ferromagnetism can be related to percolation of a particular contact configuration of C-60 molecular orientations.