Dynamical solitons in a spin S=1 ferromagnet

作者：Ivanov B A^*; Khimin R S

来源：Low Temperature Physics, 2008, 34(3): 182-191.

DOI：10.1063/1.2887870

A semiclassical theory of the spin dynamics for a ferromagnet with spin S=1 is constructed taking account of the isotropic exchange interaction. For such a ferromagnet in the ground state the quantum average value m of the spin at a site takes its maximum value, but the effects of a quantum reduction of the spin are strongly manifested in dynamics. However, for such ferromagnets there exists a special class of spin oscillations in which the direction of m is maintained but the length of m change substantially. Such excitations are absent for ordinary Heisenberg ferromagnets, whose description is based on the Landau-Lifshitz equation or on the standard Heisenberg spin Hamiltonian. Spin excitations with finite energy, or solitons, which can be regarded as bound states of a large number N of magnons, are obtained analytically in the continuum approximation and numerically. The dependence of the energy E(P, N) of a soliton with a fixed number of bound magnons on its momentum P is found. The continuum approximation gives a good description of solitons in this range of parameters, where the magnetization in a soliton differs substantially from the neighboring lattice sites and effects due to discreteness should be substantial.

• 出版日期2008-3