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

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The measurements of magnetic heat capacity and susceptibility of one-dimensional S=1 antiferromagnet (CH_3)_4NNi(NO_2)_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. 0K 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% of Nk_B ln 3, which denies the possibility of three-dimensional ordering of the spin system at lower temperatures. The observed susceptibility also agrees with the theory with J/k_B=-10.9 K and g=2.02 in the whole temperature region, when we take the effect from the finite length of the chains into consideration.
社団法人日本物理学会の論文
1994-03-15