Weak suppression of ferromagnetism in tetrakis(dimethylamino)ethylene-(C60)1-x(C70)x

Ferromagnetic properties of the molecular alloy complexes TDAE-(C60)1-x(C70)x (x=0.1-0.9), where TDAE is tetrakis(dimethylamino)ethylene, are studied by means of ESR and static magnetic susceptibility and magnetization experiments. Comparison of the magnetic properties of the present alloy complexes with those of TDAE-C60 and -C70 is made. The ESR g values and linewidths of these complexes remarkably increase below the Curie temperature Tc(x) at x<0.5. Moreover, these complexes with x=0.2, 0.4, and 0.5 show the S-shaped magnetization curves indicative of ferromagnetic correlation of spins below the Tc(x). The Tc(x) is suppressed with increasing x in such a way that Tc(0)=17.5 K and Tc(0.5)=6.1 K. This suppression is not so strong as one may expect for a quasi-one-dimensional itinerant ferromagnet. The three-dimensional spin correlations between C60 molecules both along the c axis and in the ab plane are important for this interesting magnetism.