OBSERVATION OF EDGE MOMENT S=1/2 IN THE DILUTED HALDANE SYSTEM (CH3)(4)NNI1-XZNX(NO2)(3)

Electron spin resonance (ESR) and magnetization measurements have been performed on the diluted Haldane system (CH3)(4) NNi1-xZnx(NO2)(3) (Zn2+:TMNIN). We observed ESR absorption from the S = 1/2 moment at the end of the Ni2+ chains at low temperatures. The dependence of the ESR absorption intensity on temperature and the concentration of Zn2+ are compared to the theory derived from the valence bond solid (VBS) model by Mitra, Halperin and Affleck (Phys. Rev, B 45 (1992) 5299). The paramagnetic contribution to the magnetization of Zn2+:TMNIN increases with Zn2+ concentration. We find that on average, one S = 1/2 moment appears on each segment of finite chains at low temperatures.