An analytical approach to determining the influence of thermal noise on the mean frequency and amplitude of a spin-transfer nano-oscillator

An axisymmetric model of a spin-transfer nano-oscillator (STNO) under the action of statistically isotropic magnetic-field fluctuations is considered. An expression for the stationary probability-density distribution of the angular coordinates of magnetization vector is analytically derived and used for determining dependences of the mean value and standard deviation of the amplitude and the mean oscillation frequency on the magnitude of current. The phenomenon of noise-induced shifts of the mean values of STNO amplitude and frequency is discovered. The latter effect qualitatively explains the experimentally observed dependences of the generation frequency on the STNO current.