Thermodynamic Properties of the One-Dimensional Ising System (CH_3)_4NCo(NO_2)_3, the Iso-Structural Compound with the Haldane System, TMNIN

Abstract

We measured the magnetic heat capacity, susceptibility andmagnetization of (CH₃)₄NCo(NO₂)₃ (TMCON) which is theiso-structural compound with the Haldane compound(CH₃)₄NNi(NO₂)₃ (TMNIN). From the analysis of thesethermodynamic properties, we found that TMCON is a one-dimensionalS=1/2 Ising system where the ferromagnetic nearest neighborinteraction J₁ and the antiferromagnetic next-nearest neighborinteraction J₂ are competing. The value of J₁ is estimated to beJ₁/k_B=28.0± 4.0 K. It is confirmed that the results can becomprehensively explained only when we take J₂<0, althoughJ₂=-0.22J₁ estimated from the thermal analysis differs fromJ₂=-0.46J₁ from the magnetic susceptibility for the powderedsample. Based on the results for TMCON, we discuss the stabilizationof the Haldane state in TMNIN, considering the frustration effectbetween J₁ and J₂.