Features of the coupled nuclear-electron spin precession in the Bose–Einstein condensate of magnons

The experimental detection of the Bose-Einstein condensate of magnons in coupled nuclear-electron spin precession in antiferromagnets brings the prospect of its use for magnonics and computer calculations. In particular, an attractive feature of such systems is a relatively large spin coherence time compared to traditional iron yttrium garnet samples. However, the observed Bose-Einstein condensation of magnons contradicts the Suhl-Nakamura model and the Bloch equations, which are usually used for these systems. The results of a direct experiment in antiferromagnetic MnCO$_3$ performed in this work indicate that the Suhl-Nakamura model and the Bloch equations cannot adequately describe the coupled nuclear-electron spin motion at large levels of magnon excitation.