Fabrication of Magnetic Tunnel Junction with Co2MnSi(110) Epitaxial Film

Abstract

According to Julliere's model, magnetic tunnel junctions (MTJs) with half-metallic electrodes lead to a large tunnel magnetoresistance (TMR) ratio. A Co2MnSi Heusler alloy is theoretically expected to exhibit half-metallicity. We fabricated (110)-oriented epitaxial Co2MnSi electrodes on sapphire substrates using W and Ta/W/Cr buffer layers. With the W buffer layer, we found that the W and Co2MnSi layers formed a twin structure. However, with the Ta/W/Cr multi-buffer layers, we succeeded in fabricating a high-quality Co2MnSi(110) epitaxial electrode. We fabricated a MTJ with the high-quality Co2MnSi(110) electrode and investigated TMR effects in the MTJ. As a result, we observed a TMR ratio of about 40% at room temperature and 120% at 2 K.

Tunnel Magnetoresistance Effect in Magnetic Tunnel Junctions Using a Co2MnSi(110) Electrode

“…12. Then, we formed a Mg(0 -1.3 nm)/Al(1.3 nm)-oxide layer as a tunnel barrier by O 2 plasma; we changed the plasma oxidation time (t ox ) from 10 to 240 s to optimize the tunnel barrier and Co 2 MnSi/Al-oxide interface conditions.…”

“…Subsequently, the Co 2 MnSi(30 nm) layer was deposited and post-annealed at 400 C. We confirmed that the Co 2 MnSi layer has a high-quality (110) epitaxial structure and a very flat surface using X-ray diffractometry and atomic force microscopy, for which details are in ref. 12. Then, we formed a Mg(0 -1.3 nm)/Al(1.3 nm)-oxide layer as a tunnel barrier by O 2 plasma; we changed the plasma oxidation time (t ox ) from 10 to 240 s to optimize the tunnel barrier and Co 2 MnSi/Al-oxide interface conditions.…”