Spin-dependent resonant tunneling through quantum-well states in magnetic metallic thin films

TL;DR

This paper investigates spin-dependent resonant tunneling through quantum-well states in magnetic layers, revealing conditions for resonance, significant conductance increases, and implications for advanced spintronic device design.

Contribution

It provides first-principles calculations identifying conditions for resonant tunneling in magnetic multilayers, highlighting the impact on conductance and magnetoresistance.

Findings

Sharp quantum-well states form in Fe layers.

Conductance jumps occur as QW states enter the transport window.

Magnetoresistance ratios are significantly enhanced and spin-dependent.

Abstract

Quantum-well (QW) states in {\it nonmagnetic} metal layers contained in magnetic multilayers are known to be important in spin-dependent transport, but the role of QW states in {\it magnetic} layers remains elusive. Here we identify the conditions and mechanisms for resonant tunneling through QW states in magnetic layers and determine candidate structures. We report first-principles calculations of spin-dependent transport in epitaxial Fe/MgO/FeO/Fe/Cr and Co/MgO/Fe/Cr tunnel junctions. We demonstrate the formation of sharp QW states in the Fe layer and show discrete conductance jumps as the QW states enter the transport window with increasing bias. At resonance, the current increases by one to two orders of magnitude. The tunneling magnetoresistance ratio is several times larger than in simple spin tunnel junctions and is positive (negative) for majority- (minority-) spin resonances, with a large asymmetry between positive and negative biases. The results can serve as the basis for novel spintronic devices.