No Access Submitted: 28 May 2020 Accepted: 30 August 2020 Published Online: 23 September 2020
Appl. Phys. Lett. 117, 122409 (2020);
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  • Shinto Ichikawa
  • P.-H. Cheng
  • Hiroaki Sukegawa
  • Tadakatsu Ohkubo
  • Kazuhiro Hono
  • Seiji Mitani
  • Katsuyuki Nakada
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.
We are grateful to T. Scheike for his technical support with the sputtering process and K. Masuda and Y. Miura for their valuable comments. P.-H.C. acknowledges the National Institute for Materials Science for the provision of the NIMS Graduate Research Assistantship.
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  1. © 2020 Author(s). Published under license by AIP Publishing.