Effect of Magnon-Magnon Interaction on Spin Wave Dispersion and Magnon Sideband in MnS

The temperature-dependent magnon energies and magnon sidebands in MnS have been studied theoretically by the spin wave approximation including magnon-magnon interaction and neglecting exciton-magnon interaction. Results found are: (1) the temperature renormalization factor for magnon energies depends strongly on magnon wavevector and is different from that for the sublattice magnetization; (2) the line shape is insensitive to temperature, and the peak position, which corresponds to the magnon energy at k =1.2_π[1, 1, 0]/a, shifts slowly with temperature; (3) the integrated intensity of the cold band is almost constant at low temperatures but decreases slightly with increasing temperature in contrast to a rapid increase predicted from the free spin wave theory. For the hot band, the intensity increases more slowly than predicted from the free spin wave theory. The total intensity increases gradually with temperature. The sublattice magnetization, the peak position, and the integrated intensity as functions of temperature are compared with observed results.