2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/16449We report point by point measurements below the blocking temperature of the magnetic relaxation of Mn$_{12}$-acetate as a function of magnetic field applied along the easy axis of magnetization. Unexpectedly complex structure is observed which we attribute to the effect of higher-order terms of the spin Hamiltonianon on the tunneling process.4 pages. Revised version includes new references and acknowledgmentsCondensed Mattertext