Auto-oscillation threshold, narrow spectral lines, and line jitter in spin-torque oscillators based on MgO magnetic tunnel junctions

TL;DR

This paper reports on the demonstration of spin-torque induced auto-oscillations in MgO-based magnetic tunnel junctions, achieving narrow spectral lines and stable oscillations at room temperature, with implications for high-coherence spintronic devices.

Contribution

It presents the first observation of auto-oscillations in MgO magnetic tunnel junctions with narrow spectral lines and analyzes their phase coherence and dependence on magnetic configurations.

Findings

Spectral line narrowing to 6 MHz at 300K

Auto-oscillations occur even at zero applied field

Oscillations exhibit microsecond phase coherence and millisecond power autocorrelation

Abstract

We demonstrate spin torque induced auto-oscillation in MgO-based magnetic tunnel junctions. At the generation threshold, we observe a strong line narrowing down to 6 MHz at 300K and a dramatic increase in oscillator power, yielding spectrally pure oscillations free of flicker noise. Setting the synthetic antiferromagnet into autooscillation requires the same current polarity as the one needed to switch the free layer magnetization. The induced auto-oscillations are observed even at zero applied field, which is believed to be the acoustic mode of the synthetic antiferromagnet. While the phase coherence of the auto-oscillation is of the order of microseconds, the power autocorrelation time is of the order of milliseconds and can be strongly influenced by the free layer dynamics.