2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/25911The S=1/2 Heisenberg chain with bond alternation and randomness of antiferromagnetic (AFM) and ferromagnetic (FM) interactions is investigated by quantum Monte Carlo simulations of loop/cluster algorithm. Our results have shown interesting finite temperature magnetic properties of this model. The relevance of our study to the observed results of the material (CH$_3$)$_2$CHNH$_3$Cu(Cl$_x$Br$_{1-x}$)$_3$ is discussed.5 pages, 9 figures, paper submit to conference ""Non-Perturbative Quantum Field Theory: Lattice and Beyond", Guangzhou, P.R. China, Nov. 2004Disordered Systems and Neural NetworksMaterials Sciencetext