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Tunnel Magnetoresistance and Spin-Transfer-Torque Switching in Polycrystalline ${Co}_{2} FeAl$ Full-Heusler-Alloy Magnetic Tunnel Junctions on Amorphous $Si / {SiO}_{2}$ Substrates

Zhenchao Wen, Hiroaki Sukegawa, Shinya Kasai, Koichiro Inomata, and Seiji Mitani

National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047, Japan

Phys. Rev. Applied 2, 024009 – Published 29 August, 2014

DOI: https://doi.org/10.1103/PhysRevApplied.2.024009

Abstract

We study polycrystalline $B 2$ -type ${Co}_{2} FeAl$ (CFA) full-Heusler-alloy-based magnetic tunnel junctions (MTJs) fabricated on a $Si / {SiO}_{2}$ amorphous substrate. Polycrystalline CFA films with a (001) orientation, a high $B 2$ ordering, and a flat surface are achieved by using a MgO buffer layer. A tunnel magnetoresistance ratio up to 175% is obtained for a MTJ with a $CFA / MgO / CoFe$ structure on a 7.5-nm-thick MgO buffer. Spin-transfer-torque-induced magnetization switching is achieved in the MTJs with a 2-nm-thick polycrystalline CFA film as a switching layer. By using a thermal activation model, the intrinsic critical current density ( $J_{c 0}$ ) is determined to be $8.2 \times 10^{6} A / {cm}^{2}$ , which is lower than $2.9 \times 10^{7} A / {cm}^{2}$ , the value for epitaxial CFA MTJs [Appl. Phys. Lett. 100, 182403 (2012)]. We find that the Gilbert damping constant ( $α$ ) evaluated by using ferromagnetic resonance measurements for the polycrystalline CFA film is approximately 0.015 and is almost independent of the CFA thickness (2–18 nm). The low $J_{c 0}$ for the polycrystalline MTJ is mainly attributed to the low $α$ of the CFA layer compared with the value in the epitaxial one (approximately 0.04).

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Tunnel Magnetoresistance and Spin-Transfer-Torque Switching in Polycrystalline ${Co}_{2} FeAl$ Full-Heusler-Alloy Magnetic Tunnel Junctions on Amorphous $Si / {SiO}_{2}$ Substrates

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Tunnel Magnetoresistance and Spin-Transfer-Torque Switching in Polycrystalline Co2FeAl Full-Heusler-Alloy Magnetic Tunnel Junctions on Amorphous Si/SiO2 Substrates

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References (56)

Tunnel Magnetoresistance and Spin-Transfer-Torque Switching in Polycrystalline ${Co}_{2} FeAl$ Full-Heusler-Alloy Magnetic Tunnel Junctions on Amorphous $Si / {SiO}_{2}$ Substrates