Transverse Susceptibilities of Ferromagnetic Spin System Interacting with Phonon Reservoir in the Spin-wave Approximation

A form of the transverse magnetic susceptibility of a ferromagnetic spin system with a uniaxial anisotropy energy and an anisotropic exchange interaction, interacting with a phonon reservoir, is derived in the spin-wave approximation in terms of the non-equilibrium thermo-field dynamics (NETFD) using the TCLE method. The transverse magnetic susceptibility for the ferromagnetic system of one-dimensional infinite spins is studied by assuming a damped oscillator model of the phonon reservoir. The higher-order effects in the spin-wave approximation are numerically investigated. It is shown that the higher-order parts cannot be neglected for the spin system of the small magnitude and for the high temperature system, but may be neglected for the spin system of the large magnitude.