2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/171260By means of the inverse techniques we analyse the evolution of purely spin-1/2 systems in homogeneous magnetic fields as well as the generation of exact solutions. Some ``evolution loops'', dynamical processes for which any state evolves cyclically, are presented, and their corresponding geometric phases are evaluated6 pages, LaTeX, Proceedings' macros included in source-file, 1 PostScript figureQuantum Physicstext