Investigation of the kinetic behaviors of the spin systems in the neighbourhood of the equilibrium

In this thesis, mixed spin-1 and spin-2 ferromagnetic system is studied by using a method which combines equilibrium theory of critical phenomena and Onsager irreversible thermodynamics. In order to obtain the relaxation of the magnetization to equilibrium in this system, we assume a small uniform external field that is applied a short while, which removes the system slightly from equilibrium. After, the system is exposed to time-depended external magnetic field. By studying the steady state solutions of the mixed spin-1 and spin-2 Ising model we analyzed magnetic dispersion and absorption factors as a function of temperature and frequency. Finally a comparison of our results to previous experimental and theoretical data is given.