Effect of defects in Heusler alloy thin films on spin-dependent tunnelling characteristics of Co2MnSi/MgO/Co2MnSi and Co 2MnGe/MgO/Co2MnGe magnetic tunnel junctions

Abstract

Fully epitaxial magnetic tunnel junctions (MTJs) with Co-based Heusler alloy Co2MnSi electrodes and a MgO tunnel barrier were fabricated with various values of Mn composition α for Co2Mn αSi in Co2MnαSi/MgO/Co 2MnαSi MTJs. The tunnel magnetoresistance (TMR) ratios at both 4.2K and room temperature (RT) increased systematically with increasing α in Co2MnαSi electrodes from Mn-deficient compositions (α < 1) up to a certain Mn-rich composition (α > 1), demonstrating high TMR ratios of 1135% at 4.2K and 236% at RT for MTJs with Mn-rich Co2MnαSi electrodes with α = 1.29. Identically fabricated Co2MnβGe δ/MgO/Co2MnβGeδ (δ = 0.38) MTJs showed similar dependence of the TMR ratio on Mn composition β, demonstrating relatively high TMR ratios of 650% at 4.2K and 220% at RT for β = 1.40. The Mn composition dependence of the TMR ratio at both 4.2K and RT observed commonly for both Co2MnSi/MgO/Co 2MnSi and Co2MnGe/MgO/Co2MnGe MTJs can be attributed to suppressed minority-spin in-gap states around the Fermi level for Mn-rich Co2MnSi and Co2MnGe electrodes. © 2010 IOP Publishing Ltd.