Tunnel magnetoresistance angular and bias dependence enabling tuneable wireless communication

TL;DR

This paper investigates how the angular and bias dependence of tunnel magnetoresistance (TMR) in magnetic tunnel junctions influences spin-transfer torque-driven oscillations, with implications for tunable wireless communication devices.

Contribution

It demonstrates experimentally and theoretically that TMR bias dependence significantly affects spin-torque oscillations, revealing a new mechanism for tuning wireless RF oscillators.

Findings

TMR bias dependence quenches spin-transfer-driven precession.

Non-monotonic frequency dependence at high currents.

Angular dependence of TMR sustains steady-state precession.

Abstract

Spin-transfer torques (STTs) can be exploited in order to manipulate the magnetic moments of nanomagnets, thus allowing for new consumer-oriented devices to be designed. Of particular interest here are tuneable radio-frequency (RF) oscillators for wireless communication. Currently, the structure that maximizes the output power is an Fe/MgO/Fe-type magnetic tunnel junction (MTJ) with a fixed layer magnetized in the plane of the layers and a free layer magnetized perpendicular to the plane. This structure allows for most of the tunnel magnetoresistance (TMR) to be converted into output power. Here, we experimentally and theoretically demonstrate that the main mechanism sustaining steady-state precession in such structures is the angular dependence of the magnetoresistance. The TMR of such devices is known to exhibit a broken-linear dependence versus the applied bias. Our results show that the TMR bias dependence effectively quenches spin-transfer-driven precession and introduces a non-monotonic frequency dependence at high applied currents. Thus we expect the bias dependence of the TMR to have an even more dramatic effect in MTJs with Mn-Ga-based free layers, which could be used to design wireless oscillators extending towards the THz gap, but have been experimentally shown to exhibit a non-trivial TMR bias dependence.