Non-stationary magnetization dynamics driven by spin transfer torque

TL;DR

This paper investigates the complex, non-monotonic behavior of magnetization precession driven by spin transfer torque in nanoscale devices, revealing two dynamical regimes and power fluctuations through micromagnetic simulations and wavelet analysis.

Contribution

It introduces a novel analysis of non-stationary magnetization dynamics, identifying two regimes and power loss phenomena in spin-torque oscillators.

Findings

Identification of two dynamical regimes with different precessional axes.

Observation of abrupt power loss at transition current.

Prediction of power modulation and disappearance at high non-linear regimes.

Abstract

This paper shows that the presence of two dynamical regimes, characterized by different precessional-axis, is the origin of the non-monotonic behavior of the output integrated power for large-amplitude magnetization precession driven by spin-polarized current in nanoscale exchange biased spin-valves. In particular, at the transition current between those two regimes exists an abruptly loss in the integrated output power. After the introduction of a time-frequency analysis of magnetization dynamics based on the wavelet transform, we performed a numerical experiment by means of micromagnetic simulations. Our results predicted that, together with a modulation of the frequency of the main excited mode of the magnetization precession, at high non-linear dynamical regime the instantaneous output power of the spin-torque oscillator can disappear and then reappear at nanosecond scale.