Two-magnon scattering and the collective excitation of spin waves

The Nonlinear Excitation of Strongly Coupled Spin Waves

“…The first term on the right hand side of equabions (21) is due to the linear excitat,ion whereas the second term becomes important in the nonlinear region, when Ia, , l approa.ches its crit,ical value, given by:…”

“…The approximate solutions (19) and (21), the transformation relations (7), (~l O ) , and (13) lead to the following approximate expression for a j , :…”