Field-induced magnetization in ferromagnetic and antiferromagnetic alternating Heisenberg chains formed in (CH3)2CHNH3CuCl3

We report measurements of the magnetization process of the gap system (CH3)(2) CHNH3 CUCl3, in which ferromagnetic-dominant ferromagnetic and antiferromagnetic alternating Heisenberg chains are formed and then a pair of ferromagnetically coupled S=1/2 spins behaves es as a spin of S = 1. The two critical fields H-c1 and H-c2, corresponding to the elimination of the energy gap and the alignment of all the spins along the direction of an external field H, are detected at 10.4T and around 44 T, respectively, on a scale of the reduced magnetic field gH/2. These values are, in principle, consistent with those estimated from the analysis of the magnetic susceptibility. The critical exponents in the formula such as M(H) proportional to (H - H-c1)(1/delta 1) and 1 - M(H) proportional to (H-c2 - H)(1/delta 2) are found to be delta(1) > 1 and delta(2) > 1.