Doping Effect of Non-Magnetic and Magnetic Impurities on Magnetic Susceptibility of the Haldane System (CH₃)₄NNi(NO₂)₃

Magnetic susceptibility measurement has been carried out on the Haldane system (CH₃)₄NNi(NO₂)₃ containing non-magnetic Zn²⁺ and magnetic Cu²⁺ impurity ions. For each impure system, magnetic susceptibility is described by the sum of two contributions; one is from the Haldane state and the other is a paramagnetic contribution. The latter contribution increases proportionally with impurity concentration. For 1D system shortened by Zn²⁺ impurity ions, the paramagnetic contribution obeys the Curie law, and its absolute value of the susceptibility is found to amount nearly 40% of the theoretical estimation for the VBS model where the spin with its value S = 1/2 appears at the both edges of 1D segments. In the case for the system with Cu²⁺ impurity ions, the paramagnetic contribution is much smaller than the results for the Zn²⁺ impure systems. This reduction of the magnetic moment of Cu²⁺ ion for 5 = 1/2 is qualitatively different from the case for the enhanced moment of Cu²⁺ ion in the anisotropic S = 1 Heisenberg antiferromagnet NENP.