Chemical and Magnetic Interface Properties of Tunnel Junctions With Co$_2$MnSi/Co$_2$FeSi Multilayer Electrode Showing Large Tunneling Magnetoresistance

Transport, as well as chemical and magnetic interface properties of two kinds of magnetic tunnel junctions (MTJs) with Co sub(2)FeSi electrode, Al-O barrier, and Co-Fe counter electrode, are investigated. For junctions with Co sub(2)FeSi single-layer electrodes, a tunnel magnetoresistance of up to 52% is found after optimal annealing for an optimal Al thickness of 1.5 nm, whereas the room temperature bulk magnetization of the Co sub(2)FeSi film reaches only 75% of the expected value. By using a [Co sub(2)MnSi/Co sub(2)FeSi] sub(times10) multilayer electrode, the magnetoresistance can be increased to 114%, corresponding to a large spin polarization of 0.74, and the full bulk magnetization is reached. For Al thickness smaller than 1 nm, the TMR of both kinds of MTJs decreases rapidly to zero. On the other hand, for 2- to 3-nm-thick Al, the TMR decreases only slowly. The Al thickness dependence of the TMR is directly correlated to the element-specific magnetic moments of Fe and Co at the Co sub(2)FeSi/Al-O interface for all Al thickness. Especially, for optimal Al thickness and annealing, the interfacial Fe moment of the single-layer electrode is about 20% smaller than for the multilayer electrode, indicating smaller atomic disorder at the barrier interface for the latter MTJ.