Task id14331

In ferromagnets at low temperatures, a noticeable contribution to thermal processes is made by oscillations in the system of polarized spin moments - spin waves, for which the dispersion law has the form w = Ak2, and the average number of quanta - magnons - in thermal equilibrium is determined by the same Planck formula as for phonons. Find out the nature of the temperature dependence of the contribution of magnons to the heat capacity of ferromagnets.