Magnetic Phase Transition of Ni(NH₃)₂Ni(CN)₄·2C₁₂H₁₀

Abstract

The magnetic susceptibility and the specific heat of Ni(NH₃)₂Ni(CN₄)·2C₁₂H₁₀ have been measured between 0.35 K and 20 K on a powder specimen. The crystalline-field splitting energy of the Ni⁺⁺-ion spin triplet is estimated to be 2.5±0.3 K with doublet ground state (S_z=±1). Together with a layer structure of the magnetic ions in this clathrate compound, the magnetic spins can be regarded as forming a two-dimensional Ising-like system. A symmetric logarithmic divergence of the specific heat is actually observed at T_N=0.800±0.005 K.