Critical exponents at the ferromagnetic transition in tetrakis(diethylamino)ethylene-C$_{60}$ (TDAE-C$_{60}$)

Abstract

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 $T_{c}=16.1\pm 0.05,$ we determine the susceptibility and magnetization critical exponents $γ=1.22\pm 0.02$ and $β=0.75 \pm 0.03$ respectively, and the field vs. magnetization exponent at $T_{c}$ of $δ=2.28\pm 0.14$. Hyperscaling is found to be violated by $Ω\equiv d^{\prime}-d \approx -1/4$, suggesting that the onset of ferromagnetism can be related to percolation of a particular contact configuration of C$_{60}$ molecular orientations.