Antiferromagnetic Spin Waves

The frequency spectrum and the damping constant of the spin waves in the two-sublattice antiferromagnetics are investigated on the quantum-statistical basis by the use of the relaxa-tion function method. (1) The line width of the magnetic resonance obtained is different from those of previous authors. It has a different exchange field, anisotropy field and temperature dependence. The temperature dependence agrees with the previous one only when the temperature is lower than the resonance frequency. (2) The damping constant of the non-uniform modes is explicitly calculated. (3) A general expression for the frequency spectrum which is valid at finite temperatures in the absence of an external magnetic field is obtained in terms of the usual and the staggered susceptibilities for a non-uniform magnetic field. (4) The frequency spectrum of the spin waves is determined, including the effect of the magnon interactions. Keffer and Loudon's result which was obtained from a semi-phenomenological discussion is confirmed.