Generation linewidth of an auto-oscillator with a nonlinear frequency shift: Spin-torque nano-oscillator

TL;DR

This paper develops a theory showing that nonlinear frequency shifts in auto-oscillators, such as spin-torque nano-oscillators, increase linewidth, with a predicted minimum linewidth at a specific magnetization angle, aligning with experimental data.

Contribution

The paper introduces a theoretical framework quantifying how nonlinear frequency shifts affect auto-oscillator linewidths, specifically applied to spin-torque nano-oscillators.

Findings

Linewidth increases due to nonlinearity in frequency shift.

Minimum linewidth occurs at a critical magnetization angle.

Theory aligns with recent experimental observations.

Abstract

It is shown that the generation linewidth of an auto-oscillator with a nonlinear frequency shift (i.e. an auto-oscillator in which frequency depends on the oscillation amplitude) is substantially larger than the linewidth of a conventional quasi-linear auto-oscillator due to the renormalization of the phase noise caused by the nonlinearity of the oscillation frequency. The developed theory, when applied to a spin-torque nano-contact auto-oscillator, predicts a minimum of the generation linewidth when the nano-contact is magnetized at a critical angle to its plane, corresponding to the minimum nonlinear frequency shift, in good agreement with recent experiments.