Spectrum of Two-Magnon non-Heisenberg Ferromagnetic Model of Arbitrary Spin with Impurity

We consider a two-magnon system in the isotropic non-Heisenberg ferromagnetic model of an arbitrary spin $s$ on a $\nu$-dimensional lattice $Z^{\nu}$. We establish that the essential spectrum of the system consists of the union of at most four intervals. We obtain lower and upper estimates for the number of three-particle bound states, i.e., for the number of points of discrete spectrum of the system.