Spin transfer torques in magnetic tunnel junctions

TL;DR

This paper reviews experimental and theoretical insights into spin transfer torque in magnetic tunnel junctions, highlighting mechanisms, quantum descriptions, and recent experimental validations, with a focus on differences from metallic spin-valves and half-metallic junctions.

Contribution

It provides a comprehensive overview of spin transfer torque mechanisms in magnetic tunnel junctions, including a new quantum description and analysis of half-metallic junctions.

Findings

Distinct properties of spin transfer in tunnel junctions compared to metallic spin-valves

Quantum mechanisms involving spin-dependent reflections and spin-filtering

Validation of theoretical models with recent experimental data

Abstract

This chapter presents a review on spin transfer torque in magnetic tunnel junctions. In the first part, we propose an overview of experimental and theoretical studies addressing current-induced magnetization excitations in magnetic tunnel junctions. The most significant results are presented and the main observable characteristics are discussed. A description of the mechanism of spin transfer in ferromagnets is finally proposed. In the second part, a quantum description of spin transport in magnetic tunnel junctions with amorphous barrier is developed. The role of spin-dependent reflections as well as electron incidence and spin-filtering by the barrier are described. We show that these mechanisms give rise to specific properties of spin transfer in tunnel junctions, very different from the case of metallic spin-valves. In the third part, the theoretical observable features of spin transfer in magnetic tunnel junctions are derived and the validity of these results is discussed and compared to recent experiments. To conclude this chapter, we study the mechanism of spin transfer in half-metallic tunnel junctions, expected to mimic MgO-based magnetic tunnel junctions.