The Numerical Comparison of Magnetic Susceptibility and Heat Capacity of TMNIN with the Result of a Quantum Monte Carlo Method for the Haldane System

Abstract

The measurements of magnetic heat capacity and susceptibility of one-dimensional S=1 antiferromagnet (CH₃)₄NNi(NO₂)₃ (TMNIN) have been carried out in order to make comparison with the theoretical results of a quantum Monte Carlo method for the Haldane system. The results for the heat capacity, which show a broad maximum around 10, K, are well reproduced by the theory with the interaction J/k_B=-12.0± 1.0, K in the temperature range T>0.2| J| S(S+1)/k_B. The low temperature heat capacity exhibits an exponential decay with gap energy Δ/k_B=5.3± 0.2, K, which gives Δ=0.44| J|, in contrast to the linear dependence on temperature as in the case for half integer spin. The residual magnetic entropy below 0.7, K is estimated to be 0.07