2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/110878This contribution describes the reorientation of the magnetization of thin ferromagnetic Heisenberg films as function of the temperature and/or an external field. Working in a rotating frame allows an exact treatment of the single-ion anisotropy when going to higher-order Green's functions. Terms due to the exchange interaction are treated by a generalized Tyablikov (RPA) decoupling.9 pages, 2 figuresStatistical Mechanicstext