A note on the Fano factor of spin-torque shot noise

The spin shot noise, which is a consequence of the discreteness of the angular momentum transfer, is present in every spin-torque experiment, such as for instance current-induced magnetization switching or current-induced domain wall motion. In particular at low temperatures, it constitutes a dominant contribution to magnetization noise. We discuss some important properties of the spin-torque shot noise and its implications for magnetization dynamics. We introduce the Fano factor of the non-equilibrium noise. For a spin-torque nano-oscillator, we calculate the voltage dependence of the Fano factor and show that there is an optimal precession angle at which the Fano factor is minimized.