Random quantum chain system: mixture of S=1/2 antiferromagnetic chains with uniform and alternating couplings

CuCl2xBr2(1-x)·2(γ-pic) (0≤x≤1) [γ-pic=4-Methylpyridine] is a rare example of random mixture of one-dimensional S=1/2 Heisenberg system with uniform (x=0) and alternating (x=1) antiferromagnetic couplings. From a systematic study of susceptibility and high-field magnetization of the mixed system, we found that the alternating ratio as well as the intrachain interaction continuously change with x, and, therefore, tunable with mixture. The ground state properties are consistent with the prediction for the random dimer phase