Abstract A theory of fast relaxation in easy-axis antiferromagnets is presented for conditions where the external magnetic field exceeds the spin-flip field. A possibility of rapid nuclear spin cooling is predicted. A theory is constructed which describes interaction between electromagnetic radiation and the nuclear subsystem. Light scattering from nuclear temperature fluctuatins is describe both quantitiatively and quantitatively. The intrinsic NMR frequency in a disordered ferromagnet is calculated. Dissipativeless hydrodynamics of a two-velocity and two-temperature “NSW-magnon liquid” in an “easy-axis” antiferromagnet is described for the case where the external field is close to the spin-flip field. The limiting behavior of heat capacity at ultra low temperatures is discussed.