Magnetic tunnel junctions with a B2-ordered CoFeCrAl equiatomic Heusler alloy

Tomoki Tsuchiya, Tufan Roy, Kelvin Elphick, Jun Okabayashi, Lakhan Bainsla, Tomohiro Ichinose, Kazuya Z. Suzuki, Masahito Tsujikawa, Masafumi Shirai, Atsufumi Hirohata, Shigemi Mizukami

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)

Abstract

The equiatomic quaternary Heusler alloy CoFeCrAl is a candidate material for spin-gapless semiconductors (SGSs). However, to date, there have been no experimental attempts at fabricating a junction device. This paper reports a fully epitaxial (001)-oriented MgO barrier magnetic tunnel junction (MTJ) with CoFeCrAl electrodes grown on a Cr buffer. X-ray and electron diffraction measurements show that the (001) CoFeCrAl electrode films with atomically flat surfaces have a B2-ordered phase. The saturation magnetization is 380emu/cm3, almost the same as the value given by the Slater-Pauling-like rule, and the maximum tunnel magnetoresistance ratios at 300 K and 10 K are 87% and 165%, respectively. Cross-sectional electron diffraction analysis shows that the MTJs have MgO interfaces with fewer dislocations. The temperature- A nd bias-voltage-dependence of the transport measurements indicates magnon-induced inelastic electron tunneling overlapping with the coherent electron tunneling. X-ray magnetic circular dichroism (XMCD) measurements show a ferromagnetic arrangement of the Co and Fe magnetic moments of B2-ordered CoFeCrAl, in contrast to the ferrimagnetic arrangement predicted for the Y-ordered state possessing SGS characteristics. Ab initio calculations taking account of the Cr-Fe swap disorder qualitatively explain the XMCD results. Finally, the effect of the Cr-Fe swap disorder on the ability for electronic states to allow coherent electron tunneling is discussed.

Original languageEnglish
Article number084403
JournalPhysical Review Materials
Volume3
Issue number8
DOIs
Publication statusPublished - 2019 Aug 5

ASJC Scopus subject areas

  • Materials Science(all)
  • Physics and Astronomy (miscellaneous)

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