Junction resistance, tunnel magnetoresistance ratio, and spin-transfer torque in Zn-doped magnetic tunnel junctions.

We report an extensive theoretical investigation of impurity doping and alloying effects to spin-polarized quantum tunneling in Fe/MgO/Fe magnetic tunneling junctions. We find that with proper impurity atoms, an optimal device characteristic regime can be established where the junction resistance Rj is nonlinearly quenched while the tunnel magnetoresistance ratio (TMR) is only linearly reduced. As a consequence, the spin transfer torque is significantly increased by a factor similar to the Rj reduction. We search for this optimal device regime using first-principles calculations by doping MgO with different impurity atoms. We predict that Zn has the desired property due to a well-balanced effect of producing gap states that mediate charge transport, thus quenching Rj, and producing relatively weak interchannel coupling to alleviate the detrimental diffusive scattering effect on the TMR. [ABSTRACT FROM AUTHOR]