Weak suppression of ferromagnetism in tetrakis(dimethylamino)ethylene-(${\mathrm{C}}_{60}$${)}_{1\mathrm{-}\mathit{x}}$(${\mathrm{C}}_{70}$${)}_{\mathit{x}}$

Ferromagnetic properties of the molecular alloy complexes TDAE-(${\mathrm{C}}_{60}$ ${)}_{1\mathrm{-}\mathit{x}}$(${\mathrm{C}}_{70}$ ${)}_{\mathit{x}}$ (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-${\mathrm{C}}_{60}$ and -${\mathrm{C}}_{70}$ is made. The ESR g values and linewidths of these complexes remarkably increase below the Curie temperature ${\mathit{T}}_{\mathit{c}}$(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 ${\mathit{T}}_{\mathit{c}}$(x). The ${\mathit{T}}_{\mathit{c}}$(x) is suppressed with increasing x in such a way that ${\mathit{T}}_{\mathit{c}}$(0)=17.5 K and ${\mathit{T}}_{\mathit{c}}$(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 ${\mathrm{C}}_{60}$ molecules both along the c axis and in the ab plane are important for this interesting magnetism.