Magnetic oscillations Excited by Concurrent Spin Injection from a Tunneling Current and a Spin Hall Current

TL;DR

This paper demonstrates that concurrent spin injection from tunneling and spin Hall currents can induce magnetic oscillations in a nano-oscillator, reducing critical currents and enabling better control and efficiency.

Contribution

It introduces a combined spin injection approach in a 3-terminal STNO, providing a quantitative model that predicts oscillation behavior and confirms key parameters experimentally.

Findings

Reduced critical tunneling current to zero with pure spin injection

Excellent agreement between experimental data and the proposed model

Independent confirmation of spin Hall angle and polarization values

Abstract

In this paper, a 3-terminal spin-transfer torque nano-oscillator (STNO) is studied using the concurrent spin injection of a spin-polarized tunneling current and a spin Hall current exciting the free layer into dynamic regimes beyond what is achieved by each individual mechanism. The pure spin injection is capable of inducing oscillations in the absence of charge currents effectively reducing the critical tunneling current to zero. This reduction of the critical charge currents can improve the endurance of both STNOs and non-volatile magnetic memories (MRAM) devices. It is shown that the system response can be described in terms of an injected spin current density $J_s$ which results from the contribution of both spin injection mechanisms, with the tunneling current polarization $p$ and the spin Hall angle $\theta$ acting as key parameters determining the efficiency of each injection mechanism. The experimental data exhibits an excellent agreement with this model which can be used to quantitatively predict the critical points ($J_s = -2.26\pm 0.09 \times 10^9 \hbar/e$ A/m$^2$) and the oscillation amplitude as a function of the input currents. In addition, the fitting of the data also allows an independent confirmation of the values estimated for the spin Hall angle and tunneling current polarization as well as the extraction of the damping $\alpha = 0.01$ and non-linear damping $Q = 3.8\pm 0.3$ parameters.