Skyrmion on magnetic tunnel junction: weaving quantum transport with micro-magnetism

Abstract

Over the last two decades, non-trivial magnetic textures, especially the magnetic skyrmion family, have been extensively explored out of fundamental interest and for diverse possible applications. Given the possible technological and scientific ramifications of skyrmion-texture on magnetic tunnel junctions (Sk-MTJs), in this work, we present a non-equilibrium Green's function (NEGF) based description of Sk-MTJs for both N\'eel and Bloch textures to capture the spin/charge current across different voltages, temperatures, and sizes. We predict the emergence of a textured spin current from the uniform layer of the Sk-MTJs, along with a radially varying, asymmetric voltage dependence of spin torque. We discuss the identification of N\'eel-type and Bloch-type skyrmions, including their helicity, based on local measurements of the spin current. We describe the tunneling magnetoresistance (TMR) roll-off in Sk-MTJs with lower cross-sectional areas and higher temperatures based on transmission spectra analysis. Additionally, considering the significant implications of MTJ scaling, we uncover the scaling effects in all skyrmion(AS)-MTJs, where both contacts host skyrmions. We demonstrate the impact of scaling on TMR, spin, and charge currents, providing a pathway for the Sk/AS-MTJs design optimization with miniaturization. We also introduce a computationally efficient, analytically grounded coupled spatio-eigen framework of NEGF, alleviating the sine qua non of the 3D-NEGF for systems that lack translational invariance in the transverse direction, such as Sk/AS-MTJs.