Coupled Solitons in Alternating Heisenberg Ferromagnetic Chains with a Small Magnon Band Gap

The coupled soliton excitations in an alternating Heisenberg ferromagnetic chain with a small magnon band gap are considered. Based on a quasi-discrete multiple scale approach, a set of coupled mode equations is derived which describe the dynamics of strongly coupled acoustic upper cut-off and optical lower cut-off modes. Coupled magnetic band gap soliton solutions are explicitly provided and their frequency properties are discussed.