No 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.