Abstract The principal mechanism of the temperature dependence of magnetization at low temperatures of a ferromagnet is believed to be due to the spin wave excitations. However, Ishikawa et al. [J. Magn. Magn. Mater. 10 (1979) 183] showed that in a number of itinerant electron ferromagnets the observed decrease in magnetization with increasing temperature is nearly twice as fast as expected from the measured spin wave spectra. Thus, Ishikawa et al. proposed the existence of some hidden excitations that are responsible for the additional decrease of magnetization. Recently, it was proposed by Kim [J. Magn. Magn. Mater. 125 (1993) L257] that phonons can be the cause of such a hidden excitation. To make this claim more persuasive, in this paper we report our finding that the magnetic roles of spin wave and phonon are treated quite parallel. Thus we expose the hitherto unknown essential similarity between phonons and spin waves.