Structural and magnetic properties and tunnel magnetoresistance for Co 2(Cr,Fe)Al and Co2FeSi full-Heusler alloys

K. Inomata, S. Okamura, A. Miyazaki, M. Kikuchi, N. Tezuka, M. Wojcik, E. Jedryka

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We have investigated the structure and magnetization of Co 2(Cr1-xFex)Al (0 ≤ x ≤ 1) and Co 2FeSi full-Heusler alloy films deposited on thermally oxidized Si (SiO2) and MgO (001) single crystal substrates by ultra-high vacuum sputtering at various temperatures. The films were also post-annealed after deposition at room temperature (RT). Magnetic tunnel junctions with a full-Huesler alloy electrode were fabricated with a stacking structure of Co2YZ (20 nm)/Al (1.2 nm)-oxide/Co75Fe25 (3 nm)/IrMn (15 nm)/Ta (60 nm) and microfabricated using electron beam lithography and Ar ion etching with a 102 νm2 junction area, where Co2YZ stands for Co2(Cr1-xFex)Al or Co2FeSi. The tunnel barriers were formed by the deposition of 1.2 nm Al, followed by plasma oxidization in the chamber. The x-ray diffraction revealed the A2 or B2 structure depending on heat treatment conditions and the substrate, but not L21 structure for the Co2(Cr 1-xFex)Al (0 ≤ x ≤ 1) films. The L21 structure, however, was obtained for the Co2FeSi films when deposited on a MgO (001) substrate at elevated temperatures above 473 K. The maximum tunnelling magnetoresistance (TMR) was obtained with 52% at RT and 83% at 5 K for a junction using a Co2(Cr0.4Fe0.6)Al electrode. While the junction using a Co2FeSi electrode with the L21 structure exhibited the TMR of 41% at RT and 60% at 5 K, which may be improved by using a buffer layer for reducing the lattice misfit between the Co2FeSi and MgO (001) substrate.

Original languageEnglish
Pages (from-to)816-823
Number of pages8
JournalJournal Physics D: Applied Physics
Issue number5
Publication statusPublished - 2006 Mar 7


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