Ferromagnetic resonance (FMR) studies of icosahedral and amorphous Al55Mn20Si25 alloys are presented; the results suggest that Mn exists in more than one type of magnetic environment. In addition, the FMR signal is due to magnetic ordering. The temperature dependence of the magnetizations, as determined from the FMR measurements, indicates that the magnetic interactions in these alloys cannot be described entirely satisfactorily in terms of simple spin-wave theories. © 1989 The American Physical Society.