Half-metallic electronic structure of Co<inf>2</inf>(Mn, Fe)Si electrodes investigated through tunneling spectroscopy for fully epitaxial magnetic tunnel junctions

Abstract

A Heusler alloy Co 2 MnSi (CMS) has been extensively studied as a promising spin source material [1,2] because of its theoretically predicted half-metallicity and high Currie temperature of 985 K. We recently demonstrated that the suppression of Co antisites at nominal Mn/Fe sites is critical to obtaining half-metallic quaternary Co 2 (Mn, Fe)Si (CMFS) [3] in a similar way as in ternary alloy CMS [1,4,5]. From the dependence of the TMR ratio of CMFS/MgO/CMFS MTJs (CMFS MTJs) on the Mn and Fe compositions in Co 2 (Mn α' Fe β' )Si 0.84 electrodes with a constant δ=α'+β'=1.40 ((Mn+Fe)-rich CMFS), we found a giant TMR ratio of 2610% at 4.2 K (429% at 290 K) for lightly Fe-doped CMFS with α'=1.24 and β'=0.16 [3].