Interface-driven giant tunnel magnetoresistance in (111)-oriented junctions

Keisuke Masuda,Hiroyoshi Itoh,Yoshio Miura

doi:10.1103/physrevb.101.144404

Abstract

We theoretically study the tunnel magnetoresistance (TMR) effect in (111)-oriented junctions Co/MgO/Co(111) and Ni/MgO/Ni(111). The Co-based junction is shown to have a TMR ratio over 2000$\%$, which is one order higher than that of the Ni-based one. The high TMR ratio is attributed to the interfacial resonance effect: The interfacial $d$-$p$ antibonding states are formed close to the Fermi level in the majority-spin channel and these states in both interfaces resonate with each other. This differs essentially from the conventional coherent tunneling mechanism of high TMR ratios in Fe(Co)/MgO/Fe(Co)(001).

Highlights

Since the observation of the giant tunnel magnetoresistance (TMR) effect in Fe(Co)/MgO/Fe(Co)(001) magnetic tunnel junctions (MTJs) [1,2], the TMR effect has long been explained by the coherent tunneling mechanism [3,4]: Bulk wave functions of the ferromagnetic electrode are selectively filtered by the MgO barrier and only the 1 wave function with half metallicity at the Fermi level passes through the barrier, leading to the high TMR ratio [Fig. 1(a)]
From the in-plane wave-vector dependencies of the conductances, we find that the TMR effect in the (111)-oriented MTJs cannot be understood from the bulk band structures of the barrier and electrodes, which is essentially different from the case of the (001)-oriented MTJs
Previous theoretical studies [3,4] have shown that the TMR effect in Fe/MgO/Fe(001) is dominated by the bulk band structures of Fe and MgO along the line corresponding to the (001) direction; in their results, GP,↑(k ) mainly contributing to the high TMR ratio has a sharp peak at k = (0, 0) =

Summary

Introduction

Since the observation of the giant tunnel magnetoresistance (TMR) effect in Fe(Co)/MgO/Fe(Co)(001) magnetic tunnel junctions (MTJs) [1,2], the TMR effect has long been explained by the coherent tunneling mechanism [3,4]: Bulk wave functions of the ferromagnetic electrode are selectively filtered by the MgO barrier and only the 1 wave function with half metallicity at the Fermi level passes through the barrier, leading to the high TMR ratio [Fig. 1(a)]. In the (001)-oriented MTJs, the interfacial states are formed in the minority-spin state [3,9] and tend to decrease the TMR ratio [10]. These motivate us to speculate that interfacial states provide significant contribution to TMR effects in real experiments and decrease the TMR ratios in Fe(Co)/MgO/Fe(Co)(001) MTJs. In contrast, we can utilize such interfacial states for enhancing the TMR effect significantly; this study proposes a quite high TMR ratio driven by the interfacial resonance effect in an unconventional (111)-oriented MTJ

Methods

Results

Conclusion