2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/18436We present experimental results on resonant spin tunnelling in a single crystal of Mn$_{12}$-2Cl benzoate with different concentration of dislocations. The time evolution of the magnetisation follows the stretched exponential over a few time decades. The values of parameters of stretched exponential deduced from experiment have been used to determine the concentration of dislocations before and after the cooling-annealing process, using the algorithm recently suggested by Garanin and Chudnovsky.7 pages, 2 figuresMaterials Sciencetext