NONLINEAR EXCITATIONS IN THE FCC ANTIFERROMAGNET CEAS

Employing the Dyson-Maleev transformation, the coherent state ansatz a nd the time-dependent variational principle, we obtain two partial dif ferential equations of motion from the Hamiltonian in the fee antiferr omagnet CeAs. By using the multiple scalar method and long-wavelength approximation, we reduce these equations to an envelope function equat ion, and we force this function to satisfy the nonlinear Schrodinger e quation. The single and two soliton bound state solutions are obtained by using the inverse scattering transformation. For the single and tw o soliton bound state, the spatial configurations of the spin are give n. These results show that the nonlinear magnon localization and the t wo magnon bound state are possible in this system. The possibility of observing a gap soliton is also discussed.