Magnetotransport Properties in Magnetic Heterojunctions: Combined First-Principles Calculation with NEGF Method and Spin Dynamics Simulation

Abstract

Recently, we have successfully employed the single-band tight-binding model to predict the noncollinear spin torque effect in insulator and spin-filter based magnetic tunnel junctions [1]. However, for real complex magnetic heterojunctions, the injected spin-polarized electrons from ferromagnetic electrode can be strongly influenced by the complicated interfacial spin-polarized charge transfer, which is normally ignored in the tight-binding model can causes discrepancy between computational results and experimental findings. Our newly developed “JunPy” [2] package has successfully combined the self-consistent Hamiltonian by using the first-principles calculation with the non-equilibrium Green’s function (NEGF) method to obtain the noncollinear spin torque effect in nm-scale magnetic heterojunctions. The divide-and-conquer (DC) method was first applied to reveal the oscillatory decay of layer-resolved spin torques away from the MgO/Fe interface, and suggests a very thin Fe layer thickness below 2 nm to preserve the efficient current-driven magnetization switch [3]. We further developed the Landau-Lifshitz-Gilbert (LLG) equation implemented by our calculated spin transfer torque (STT) effect to simulate the magnetization switching in Fe/MgO/Fe MTJ in the presence of perpendicular magnetic anisotrpy (PMA), external magnetic field, and current-induced spin transfer torque (STT). The resistance as a function of magnetic field (R-H loop) and of bias (R-V loop) are thus obtained and well comparable with experimental results. On the other hand, our “JunPy” package is applied to predict the giant field-like spin torque (FLST) effect in the amine-ended single-molecule magnetic junction [4], which can efficiently assist the molecule scale magnetic proximity effect via interfacial spin filter effect and may open a new avenue for multifunctional manipulation in next-generation organic FLST-MRAMs with lower power consumption. We believe that this newly developed “JunPy” calculation process not only can efficiently resolve current self-consistent difficulties in first-principles calculation for magnetoelectric and magnetotransport properties, but also may inspire future experimental explorations in novel magnetic heterojunctions for spintronics applications. This work is supported by the Ministry of Science and Technology of Taiwan (MOST 107-2633-M-008-004 and 108-2628-M-008-004-MY3). [1] Y. –H. Tang et al., Phys. Rev. Lett. 103, 057206 (2009); Sci. Rep. 5, 11341 (2015). [2] https://labstt.phy.ncu.edu.tw/junpy [3] B. -H. Huang et al., AIP Advacnes 11, 015036 (2021). This paper was selected as an Editor’s Pick. [4] Y. –H. Tang and B. –H. Huang, J. Phys. Chem. C 122, 20500 (2018).