Thermal magnetization noise in a thin film

The effect of thermal fluctuations on a thin film has been calculated. The technique involves adding to the basic spin dynamics a general form of interaction with a thermal bath. For a general anisotropic magnetic system the resulting equation can be written as a Langevin equation for a harmonic oscillator. Our approach predicts two times smaller noise power at low frequencies than the conventional stochastic Landau-Lifshitz-Gilbert equation. It is shown that equivalent results can be obtained by introducing a tensor form of phenomenological damping α to the gyromagnetic dynamics driven by a thermal fluctuating field. This form takes into account an ellipticity of magnetization motion.