Boosting room temperature tunnel magnetoresistance in hybrid magnetic tunnel junctions under electric bias

TL;DR

This paper introduces a novel method to significantly enhance room temperature tunnel magnetoresistance in hybrid magnetic tunnel junctions under electric bias by utilizing spin orbit coupling-controlled interfacial states in V/MgO/Fe structures.

Contribution

The study demonstrates a new approach using SOC-controlled interfacial states to boost TMR under bias, overcoming limitations of traditional symmetry filtering mechanisms.

Findings

Strong TMR increase observed with bias in V/MgO/Fe/Co hybrids.

Model explains TMR boost via nonlinear resistances in series.

Potential for new spintronic devices with bias-enhanced TMR.

Abstract

Spin-resolved electron symmetry filtering is a key mechanism behind giant tunneling magnetoresistance (TMR) in Fe/MgO/Fe and similar magnetic tunnel junctions (MTJs), providing room temperature functionality in modern spin electronics. However, the core process of the electron symmetry filtering breaks down under applied bias, dramatically reducing the TMR above 0.5 V. This strongly hampers the application range of MTJs. To circumvent the problem, resonant tunneling between ferromagnetic electrodes through quantum well states in thin layers has been used so far. This mechanism, however, is mainly effective at low temperatures. Here, a fundamentally different approach is demonstrated, providing a strong TMR boost under applied bias in V/MgO/Fe/MgO/Fe/Co hybrids. This pathway uses spin orbit coupling (SOC) controlled interfacial states in vanadium, which contrary to the V(001) bulk states are allowed to tunnel to Fe(001) at low biases. The experimentally observed strong increase of TMR with bias is modelled using two nonlinear resistances in series, with the low bias conductance of the first (V/MgO/Fe) element being boosted by the SOC-controlled interfacial states, while the conductance of the second (Fe/MgO/Fe) junctions controlled by the relative alignment of the two ferromagnetic layers. These results pave a way to unexplored and fundamentally different spintronic device schemes, with tunneling magnetoresistance uplifted under applied electric bias.