Tunnel Magnetoresistance Effect in CoFeB/MgO/Heusler Alloys(Co{sub}2FeSi,Co{sub}2MnSi) Tunnel Junctions

摘要

Recently, several groups have reported giant tunnel magnetoresistance (TMR) ratios of more than 200% in magnetic tunnel junctions (MTJs) using the MgO barrier and CoFeB ferromagnetic electrodes [1,2]. According to their report, highly textured MgO(001) barrier is the most important factor to obtain large TMR ratios experimentally. However, in the MTJs with MgO barrier, TMR ratio is restricted by hot-spot tunneling in anti-parallel magnetic configuration, as expected by theories [3]. The restriction can be removed, if hot-spot tunneling is disappeared by using half-metallic materials as one electrode of MTJs. The most interesting and attractive half-metallic material is a series of Heusler alloys. Some groups have attempted to use Co{sub}2MnSi and Co{sub}2Cr{sub}(1-x)Fe{sub}xAl as a bottom magnetic layer of MTJs [4, 5], but half-metallicity was observed only in our group, as reported previously [6]. In this study, we investigated the TMR effects in CoFeB/MgO/Heusler alloys (Co{sub}2FeSi and Co{sub}2MnSi) MTJs. Both Co{sub}2FeSi and Co{sub}2MnSi Heusler alloys have half-metallic band structure and high Curie temperature of 1200K and 985K, respectively. Moreover, the lattice mismatch between the Heusler alloys and MgO barrier is relatively small, which indicates that the highly textured Heusler alloys can be grown on the MgO barrier.