Controlling oxygen distribution of an MgAl2O4 barrier for magnetic tunnel junctions by two-step process

Abstract

An MgAl2O4 barrier with an ordered spinel structure for magnetic tunnel junctions (MTJs) was prepared via a two-step process by repeating Mg–Al alloy deposition and post-oxidation to tune its oxidation state. The obtained Fe/MgAl2O4/Fe(001) epitaxial MTJs showed a large tunnel magnetoresistance (TMR) ratio (>150%) in a wide resistance × area (RA) range; this behavior was in contrast with that of MTJs prepared through a conventional one-step process, which exhibited a large TMR ratio only in a narrow RA range. The bias voltage at which the TMR is halved from the zero-bias value increased up to 1.20 and 1.47 V for the positive and negative bias polarities, respectively, when optimizing the two-step process. The nanostructure analysis revealed an improved oxygen distribution on the atomic scale in the MgAl2O4 barrier with the two-step process, providing a coherent barrier suitable for various practical applications.

Enhanced magnetoresistance in perpendicular magnetic tunneling junctions with MgAl2O4 barrier

“…30 A two-step process with repetition of Mg-Al alloy deposition and post oxidation has also been studied. 34 At optimum oxidation state the cation-ordered spinel MAO structure was reported in contrast to the cationdisordered spinel structure from the one-step process.…”

Large magnetocapacitance of up to 456% at room temperature in FeCo/MgAl2O4/FeCo(001) magnetic tunnel junctions

“…Such asymmetric features with bias polarity are typically observed in the bias-voltage dependences of TMR and differential conductance of MAO-based MTJs prepared via a one-step postoxidation process. 28,36) The degree of oxidation differs slightly between the upper and lower MAO interfaces, thus resulting in a difference in the electronic structures that determine the TMR and conductance. This approach can also be applied to the TMC.…”