Linewidth of Power Spectrum Originated from Thermal Noise in Spin Torque Oscillator

TL;DR

This paper develops a theoretical formula for the linewidth caused by thermal noise in a spin torque oscillator, showing it can be significantly reduced with large currents, predicting high quality factors.

Contribution

It introduces a new theoretical model for linewidth in spin torque oscillators considering thermal activation, with predictions for linewidth suppression and high quality factors.

Findings

Linewidth can be reduced to 0.1 MHz with large currents.

Predicted quality factor exceeds 10^4, surpassing experimental observations.

Thermal noise effects are quantitatively modeled in the oscillator.

Abstract

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.