Epitaxial growth of full-Heusler alloy Co{sub}2 MnSi thin films on MgO-buffered MgO substrates

摘要

Cobalt-based full-Heusler thin films have recently attracted much interest as a highly desirable material for ferromagnetic electrodes in spintronic devices [1-3]. We have recently fabricated fully epitaxial magnetic tunneling junctions (MTJs) using a Co-based full-Heusler alloy thin film of either Co{sub}2Cr{sub}0.6Fe{sub}0.4Al (CCFA) [2] or Co{sub}2MnGe [4] as a lower electrode and a MgO tunnel barrier. We have also demonstrated relatively high tunnel magnetoresistance (TMR) ratios at room temperature (RT) for these epitaxial MTJs (42% for CCFA-MTJs at RT [2]). Co{sub}2MnSi (CMS) is one of the Co-based full-Heusler alloys that has been theoretically predicted to be half-metallic. Recently, epitaxial CMS thin films have been grown on Cr-buffered MgO substrates [3]. TMR ratios of 70% have been reported at RT for MTJs using the latter CMS film as a ferromagnetic electrode [3]. The lattice mismatch between CMS and MgO on a 45° in-plane rotation is -5.1%, which is contrasted to that of -2.0% between CMS and Cr. However, the epitaxial growth of CMS films on a MgO buffer layer will lead to fully epitaxial MTJs consisting of CMS lower and upper electrodes and a MgO tunnel barrier. Our purpose in the present study is to fabricate epitaxial CMS films on MgO-buffered MgO (001) substrates and to clarify the structural and magnetic properties of the fabricated CMS films.