It is shown that the precise temperature dependence of the spontaneous magnetization depends on the domain structure and, additionally, on the macroscopic dimensions of the sample. In the multi-domain zero-field ground state of cubic ferromagnets (or antiferromagnets) with half-integer spin, thermal decrease of the spontaneous magnetization is by universal T2 function up to crossover to critical power function. Power functions of temperature that hold over a large temperature range and are independent of spin structure are the typical indication that the spin dynamics is controlled by a boson field. For the magnets with half-integer spin, the T2 function means a three-dimensional boson field. In the mono-domain state prepared by ferromagnetic saturation, all moments are oriented parallel to the field axis. For this one-dimensional spin configuration the boson field can be anticipated to be one-dimensional and the spontaneous magnetization should decrease according to universal T5/2 function (for S = half-integer). However, only for sufficiently large samples the T5/2 function is confirmed. For smaller samples successive crossover events in the sequence T2 → T3/2 → T5/2 can occur for increasing temperature. Occurrence of boson fields with a higher dimensionality (T2, T3/2) in the state of ferromagnetic saturation can be explained by scattering processes of the bosons at the inner surface of the sample. When the diameter of the sample is less than the mean free path of the bosons, all bosons will be reflected (or scattered) at the inner surface of the sample and the resulting boson field can become three-dimensional (T2 universality class). A one-dimensional spin orientation due to the applied demagnetization field but a three-dimensional boson field that controls spin dynamics is possible only for the T2 universality class because there is nearly no interaction between boson field and spins (magnons) in this universality class. With increasing temperature the mean free path of the bosons decreases and only a fraction of the bosons gets scattered at the inner surface of the sample. Crossover to T3/2 function and, eventually, to T5/2 function then can occur. A similar situation as for the polarized ferromagnets is observed in the axial-symmetric zero-field ground state of the hcp ferromagnet cobalt. Only for sufficiently large samples scattering of the bosons at the inner surface of the sample is of no importance and the intrinsic T5/2 function, typical for parallel alignment of all spins, shows up. The mean free path of the bosons can be estimated to be of the order of a few mm for T → 0.