A theoretical formula of the linewidth caused by the 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 down 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 the recently observed experimental value.
@article{arxiv.1404.6558,
title = {Linewidth of Power Spectrum Originated from Thermal Noise in Spin Torque Oscillator},
author = {Tomohiro Taniguchi},
journal= {arXiv preprint arXiv:1404.6558},
year = {2014}
}