Unconventional bias dependence of tunnel magnetoresistance induced by the Coulomb blockade effect

Ryota Suzuki,Le Duc Anh,Yuriko Tadano,Shinobu Ohya,Masaaki Tanaka

doi:10.1063/5.0077052

Abstract

In conventional magnetic tunnel junctions (MTJs), the tunnel magnetoresistance (TMR) monotonically decreases with increasing bias voltage, which limits the bias voltage range for the operation of MTJs. In our study, using double-barrier MTJs composed of Fe/MgO/Fe/γ-Al2O3 grown on a Nb-doped SrTiO3 substrate, we demonstrate unconventional bias dependences of the TMR, in which the TMR ratio increases with increasing bias voltage. We reveal that this behavior originates from the sharp giant resistance peak near zero bias likely induced by the Coulomb blockade effect via Fe impurities in γ-Al2O3, which are diffused from the Fe layer. The observed TMR ratio is 23% at a bias voltage of −4 V at 3.5 K, which is a very high value in this large bias voltage range. Our results offer a novel way to improve the bias voltage dependence of TMR.

Highlights

G scitation.org/journal/adv regime in the EuS layer
A similar behavior has been observed in several quasimagnetic tunnel junction (QMTJ) with various spin-filter barriers, such as CoFe2O4,14 EuO,15 and Sm0.75Sr0.25MnO3.16 Enhanced tunnel magnetoresistance (TMR) in the high bias voltage range via a quantum size effect has been reported;17–23 in double-barrier MTJs (DBMTJs) with a ferromagnetic quantum well, TMR can be strongly enhanced by resonant tunneling through spin-split quantum levels, in which carriers are perfectly spin polarized
In this paper, using DBMTJs composed of Fe/MgO/Fe/γ-Al2O3 grown on Nb-doped SrTiO3 (Nb:STO) substrates, we report unconventional bias dependences of the TMR, in which the TMR ratio increases with increasing bias voltage

Summary

Introduction

G scitation.org/journal/adv regime in the EuS layer. A similar behavior has been observed in several QMTJs with various spin-filter barriers, such as CoFe2O4,14 EuO,15 and Sm0.75Sr0.25MnO3.16 Enhanced TMR in the high bias voltage range via a quantum size effect has been reported;17–23 in DBMTJs with a ferromagnetic quantum well, TMR can be strongly enhanced by resonant tunneling through spin-split quantum levels, in which carriers are perfectly spin polarized. In this paper, using DBMTJs composed of Fe/MgO/Fe/γ-Al2O3 grown on Nb-doped SrTiO3 (Nb:STO) substrates, we report unconventional bias dependences of the TMR, in which the TMR ratio increases with increasing bias voltage.

Results

Conclusion