Magnetoresistance and spin-transfer torque in magnetic tunnel junctions

TL;DR

This paper reviews recent advances and unresolved issues in magnetic tunnel junctions, focusing on their magnetoresistance, spin-transfer torque effects, and potential applications in magnetic memory and sensors.

Contribution

It highlights current progress and identifies key open questions regarding the fundamental properties and behaviors of magnetic tunnel junctions.

Findings

Magnetoresistance properties vary with tunnel-barrier thickness and bias.

Spin-transfer torque effects are significant for magnetic switching.

MTJs are promising for nonvolatile magnetic memory applications.

Abstract

We comment on both recent progress and lingering puzzles related to research on magnetic tunnel junctions (MTJs). MTJs are already being used in applications such as magnetic-field sensors in the read heads of disk drives, and they may also be the first device geometry in which spin-torque effects are applied to manipulate magnetic dynamics, in order to make nonvolatile magnetic random access memory. However, there remain many unanswered questions about such basic properties as the magnetoresistance of MTJs, how their properties change as a function of tunnel-barrier thickness and applied bias, and what are the magnitude and direction of the spin-transfer-torque vector induced by a tunnel current.