Origin of charge transfer phase transition and ferromagnetism in (C_nH_2n+1)₄N[Fe^IIFe^III(dto )₃] (dto=C₂O₂S₂)

Mixed-valence complex (n-C₃H₇)₄N[Fe^IIFe^III(dto) ₃] (dto=C₂O₂S₃) shows a new-type of phase transition coupled with spin and charge around 120 K, where the charge transfer between the Fe^II and Fe^III sites occurs reversibly, and shows the ferromagnetic transition at 6.5 K. We have investigated the transport and magnetic properties for the single crystal of (n-C₃H₇)₄N[Fe^IIFe^III(dto) ₃]. Both of the intra- and interlayer resistivity showed an anomalous drop due to the charge transfer phase transition. The anisotropy of the magnetization implied that the spins in the ferromagnetic ordered state were aligned parallel to the layer of [Fe^IIFe^III (dto)₃]∞.