We have studied the field dependence of the heat capacity of a typical Haldane antiferromagnet (CH3)4NNi(NO)3 (TMNIN) doped with the nonmagnetic impurity Zn2+, as well as of a pure TMNIN. The overall features of the magnetic heat capacity, including the characteristic broad maximum, are almost reproduced by the theoretical curve with J/kB = -12K for both systems in zero field. The field dependence in the impure systems is described well by assuming the Schottky heat capacity with S = 1, not S = 1/2 expected from the VBS model. A possible reason why the S = 1 model is suitable is discussed.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)