Green's function of a uniaxial ferromagnet with single-ion anisotropy and arbitrary spin in the canted phase

For a uniaxial ferromagnet with single-ion anisotropy and arbitrary spin $S$ the Green's function is calculated in the case of magnetization along the hard axis. It is shown that the system has $4S$ types of excitation, consisting of $2S$ modes of opposite signs. At low temperatures, one spin-wave branch is excited, with the consequence that the thermodynamic behavior of the system is particularly simple.