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 $\gamma =1.22\pm 0.02$ and $\beta =0.75\pm 0.03$ respectively, and the field vs. magnetization exponent at $T_c$ of $\delta =2.28\pm 0.14$. Hyperscaling is found to be violated by $\Omega \equiv d^{\prime }-d\approx -1/4$, suggesting that the onset of ferromagnetism can be related to percolation of a particular contact configuration of C${}_{60}$ molecular orientations.

5 pages, including 3 figures; to appear in Phys. Rev. Lett

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