Impact of interfacial termination on L10-MnAl spin torque perpendicular magnetic tunnel junctions: A DFT-NEGF study

Abstract

L 1 0 -ordered MnAl is a promising material for designing perpendicular magnetic tunnel junctions (MTJs), thanks to its unique properties, such as high bulk perpendicular magnetic anisotropy, thermal stability, and low Gilbert damping. To elucidate its potential, we present here a comprehensive first-principles analysis of spin-dependent transport in MnAl/MgO-based MTJs and systematically investigate the tunneling conductance, tunneling magnetoresistance (TMR), the Resistance-Area (RA) product, spin-transfer torque (STT), and critical power (Pc) for STT switching. We particularly focus on the impact of MnAl surface terminations at the MnAl/MgO junctions, MgO thickness, and the interfacial strain, which influences the performance of MTJs. Although MnAl exhibits symmetry-driven spin filtering through the MgO barrier, our results show that the surface termination critically influences spin conductance. For a barrier thickness of ∼1 nm, a significant variation in TMR is observed, reaching values as high as 3972%, a low RA of 4.59Ωμm2, and a maximum STT of 29.11μeV/V depending on the surface termination. Although Fe-based systems exhibit comparable Pc to MnAl-based systems, the latter demonstrate higher thermal stability and scalability. While increasing MgO thickness, we observe an increase in TMR, however, at a cost of exponentially increasing RA and Pc, irrespective of the surface terminations. We finally highlight how strain modulates the electronic states at the interface and influences the spin transport and magnetization switching in these MTJs.