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 (CH 3 ) 4 NNi(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±1.0 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% of N k 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 fro...