Thermal and Magnetic Properties of Linear Ferro- and Autiferro-Magnetic Substances, MCl2·2NC5H5(M; Co, Cu)

Abstract

The magnetic specific heat of CoCl ₂ ·2NC ₅ H ₅ agreed with the exact solution of the ferromagnetic Ising linear chain with J / k =9.5±0.2 K above 6 K. The broad maximum expected theoretically to appear at 3.9±0.15 K was observed at 4.3±0.2 K. The magnetic susceptibility of this salt showed the rapid increase which is also the characteristic of the ferromagnetic Ising linear chain. About 85% of the total magnetic entropy Rln 2 was left above the Néel point 3.17±0.02 K. The characteristic features of the antiferromagnetic linear chain of the isotropic Heisenberg spins were obtained in the case of CuCl ₂ ·2NC ₅ H ₅ : The magnetic susceptibility quite agreed with the one calculated theoretically for | J |/ k =13.6±0.8 K and g =2.06±0.06. The linear dependence of the specific heat on temperature in the lowest temperature region, which is expected theoretically, was ascertained experimentally for the first time. The absolute experimental values of the magnetic specific heat agreed with the theoretical ones for | J |/ k =11.5±0.4 K.