Influence of film composition in Co2MnSi electrodes on tunnel magnetoresistance characteristics of Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions

Fully epitaxial Co2MnSi (CMS)/MgO/CMS magnetic tunnel junctions (MTJs) with various values of Mn composition α in Co2MnαSi electrodes were fabricated and the influence of α on the tunnel magnetoresistance (TMR) characteristics of these MTJs was investigated. MTJs with Mn-rich CMS electrodes showed TMR ratios, up to 1135% at 4.2 K and 236% at room temperature for α = 1.29, exceeding those of MTJs with CMS electrodes having an almost stoichiometric composition. A possible origin of the higher TMR ratios for α beyond 1.0 is a decreased density of gap states existing around the Fermi level in the half-metal gap caused by the suppression of Co_[Mn] antisites, where a Mn site is replaced by a Co atom, for Mn-rich CMS electrodes.