Origin of the spectral linewidth in non linear oscillators based on MgO tunnel junctions

TL;DR

This paper investigates the origins of spectral linewidth in MgO-based spin transfer oscillators, revealing the roles of oscillator nonlinearity, temperature independence, and magnetization chaotization in linewidth broadening.

Contribution

It demonstrates the impact of oscillator nonlinearity and spin transfer torque on linewidth, highlighting noise sources beyond thermal fluctuations in MgO tunnel junctions.

Findings

Linewidth is largely unaffected by temperature changes.

Low current linewidth enhancement linked to increased nonlinearity.

Noise is dominated by magnetization chaotization, not thermal fluctuations.

Abstract

We demonstrate the strong impact of the oscillator agility on the line broadening by studying spin transfer induced microwave emission in MgO-based tunnel junctions with current. The linewidth is almost not affected by decreasing the temperature. At very low currents, a strong enhancement of the linewidth at low temperature is attributed to an increase of the non linearity, probably due to the field-like torque. Finally we evidence that the noise is not dominated by thermal fluctuations but rather by the chaotization of the magnetization system induced by the spin transfer torque.