Magnetic torque and ac and dc magnetic susceptibility measurements on PTMA0.5[Fe(Pc)(CN)2]･CH3CN: Origin of spontaneous magnetization in [Fe(Pc)(CN)2] molecular conductors

Magnetic torque (3≤T≤46 K), dc magnetic susceptibility (2≤T≤300 K), and ac magnetic susceptibility (2≤T≤30 K) are reported for PTMA0.5[Fe(Pc)(CN)2]･CH3CN. The torque curves exhibit a sinusoidal line shape for temperatures above 6 K. This result as well as the temperature dependence of the dc magnetic susceptibility above 13 K was analyzed by employing an anisotropic Heisenberg model in one dimension. The compound exhibits spontaneous magnetization below 6 K. The torque measurements at 3 K revealed that the direction of this spontaneous magnetization is parallel to the easy axis of the mother antiferromagnetism. The ac susceptibility measurements demonstrated the fluctuation of the spontaneous magnetization up to 13 K. A model of charge-ordered ferrimagnetism is proposed in order to explain these results. This model explains the spontaneous magnetization which commonly appears in conducting salts of [Fe(Pc)(CN)2] and their derivatives.