In order to establish an expression for the ferromagnetic resonance frequency of specimen with general shape, the Landau-Lifschitz-Gilbert differential equation was solved by considering demagnetisation effects and damping. By beginning the approach of calculation in a three dimensional space the sample was regarded as a uniformly magnetised ferro- or ferrimagnetic conventional ellipsoid. The condition for calculation must be a one-domain state which can be obtained by introducing a marked uniaxial anisotropy field and/or by applying an external magnetic saturation field. This can now be put on the level with a macro-spin precessing about its preferred direction. As a result, a more exact solution for the ferromagnetic resonance frequency was achieved which takes the phenomenological damping parameter as well as the demagnetisation factors into account. Applying it to certain sample shapes (plane, spherical or cylindrical) the uniaxial anisotropy field, the saturation magnetisation and especially the damping parameter show a different impact on the resonance frequency value. It could be shown that a plane sample (film) is more influenced by the damping parameter.

Elementary excitations in antiferromagnets are magnons, and these quasiparticles with integer spin are governed by Bose statistics. In certain conditions their density can be controlled by applied radiofrequency pulse leading to the formation of Bose-Einstein condensation (BEC). We report the investigations of free induction decay signal duration in CsMnF₃ under different conditions and discuss it in the framework of the magnon BEC. The observed results in CsMnF₃ and previous investigations in superfluid ³He-A are compared.