Nonequilibrium Green's Function and First-Principles Approach to Modeling of Multiferroic Tunnel Junctions

Recently, multiferroic tunnel junctions (MFTJs) have gained significant attention in the literature due to their high tunneling electroresistance together with their nonvolatility. To analyze such devices and to have an insightful understanding of their characteristics, there is a need to develop a multiphysics modeling-and-simulation framework. The simulation framework discussed in this paper is motivated by the scarcity of such multiphysics studies in the literature. In this study, a theoretical analysis of MFTJs is demonstrated with use of a self-consistent analysis by a spin-based nonequilibrium Green's function method to estimate the tunneling current, the Landau-Khalatnikov equation to model the ferroelectric polarization dynamics, and the Landau-Lifshitz-Gilbert equation to capture the magnetization dynamics. The spin-based nonequilibrium Green's function method is equipped with a magnetization-dependent Hamiltonian that eases the modeling of the tunneling electroresistance, the tunneling magnetoresistance, and the magnetoelectric effect in MFTJs. Moreover, we perform first-principles calculations to estimate the screening lengths of the MFTJ electrodes that are necessary for estimation of the tunneling current. The simulation results of the proposed framework are in good agreement with the experimental results. Finally, a comprehensive analysis of tunneling electroresistance and tuneling magnetoresistance of MFTJs and their dependence on various device parameters is provided.