2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/157524We present a microscopic theory for the phonon-driven decay of the magnetization fluctuations in a wide class of nanomagnets where the dominant energy is set by isotropic exchange and/or uniaxial anisotropy. Based on the Zwanzig-Mori projection formalism, the theory reveals that the magnetization fluctuations are governed by a single decay rate $ω_c$, which we further identify with the zero-frequency portion of the associated self-energy. This dynamical decoupling from the remaining slow degrees of freedom is attributed to a conservation law and the discreteness of the energy spectrum, and explains the omnipresent mono-exponential decay of the magnetization over several decades in time, as observed experimentally. A physically transparent analytical expression for $ω_c$ is derived which highlights the three specific mechanisms of the slowing down effect which are known so far in nanomagnets.7 pagesMesoscale and Nanoscale PhysicsOther Condensed Mattertext