Short description of important scientific result: We report the observation of the unusual behavior of induction decay signals in antiferromagnetic
monocrystals with Suhl-Nakamura interactions. The signals show the formation of the Bose-Einstein
condensation (BEC) of magnons and the existence of spin supercurrent, in complete analogy with the spin
superfluidity in the superfluid 3He and the atomic BEC of quantum gases. In the experiments described
here, the temperature of the magnon BEC is a thousand times larger than in the superfluid 3He. It opens a
possibility to apply the spin supercurrent for various magnetic spintronics applications