Negative correlation between the linear and the nonlinear conductance in magnetic tunnel junctions

TL;DR

This study reveals a fundamental negative correlation between linear and nonlinear conductance in magnetic tunnel junctions, indicating an intrinsic mechanism possibly involving magnon-assisted spin-flip tunneling, beyond standard models.

Contribution

It uncovers a universal negative correlation between linear and nonlinear conductance in MTJs and proposes a phenomenological model involving magnon-assisted spin-flip tunneling.

Findings

Negative correlation between linear and cubic conductance coefficients.

The correlation persists across temperature and barrier thickness.

Standard tunneling models cannot fully explain the observations.

Abstract

The current-voltage ($IV$) characteristics beyond the linear response regime of magnetic tunnel junction (MTJ) is systematically investigated. We find a clear negative correlation between the two coefficients to characterize the linear ($I$$\propto$$V$) and the lowest-order nonlinear ($I$$\propto$$V^3$) currents, which holds regardless of the temperature and the thickness of the tunnel barrier. This observation cannot simply be explained by the standard tunneling model such as the Brinkman model, suggesting a mechanism intrinsic to MTJ. We propose a phenomenological model based on the Julli\'ere model that attributes the observed negative correlation to the spin-flip tunneling assisted by a magnon. These results suggest a fundamental law between the linear and the nonlinear response of MTJ.