Linewidth of power spectrum originated from thermal noise in spin torque oscillator

A theoretical formula for the linewidth caused by thermal activation in a spin torque oscillator with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer was developed by solving the stochastic Landau–Lifshitz–Gilbert equation in the energy-phase representation. It is shown that the linewidth can be suppressed to 0.1 MHz by applying a large current (10 mA for typical material parameters). A quality factor larger than 10 4 is predicted in the large current limit, which is two orders of magnitude larger than a recently observed experimental value.