SOLITON SPIN EXCITATIONS IN AN ANISOTROPIC HEISENBERG FERROMAGNET WITH OCTUPOLE-DIPOLE INTERACTION

We investigate the nonlinear spin dynamics of an anisotropic Heisenberg ferromagnetic spin chain with octupole-dipole interaction in the semiclassical limit using the coherent-state method combined with the Holstein-Primakoff bosonic representation of spin operators. The dynamics is found to be governed by a generalized nonlinear Schr\"odinger equation in the continuum limit. For specific values of the exchange, octupole-dipole interactions, and also of the anisotropy parameters, through Painlev\'e singularity structure analysis, we have identified an integrable spin chain model with soliton spin excitations. We carry out a multiple scale perturbation analysis to find the discreteness effect on the soliton excitations in the more general nonintegrable case.

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