Electronic and Spin Transport Properties of Fe/MgO/Fe Magnetic Tunnel Junction: Combined First-Principles Calculation and TB-NEGF Method

• Main Authors: Chia-Chia Chao, 趙家加
• Other Authors: 唐毓慧
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/yrw7be

碩士 === 國立中央大學 === 物理學系 === 107 === Magnetic tunnel junctions (MTJs) have aroused intensive studies for applications in non-volatile magnetic random access memories (MRAMs), which have been widely used, and the most important property of MTJs is the tunneling magnetoresistance (TMR) effect. The giant magnetoresistance (MR) ratio originates from the tunneling current depending on the relative orientation of two FM electrodes that can be controlled by a spin-polarized current via the so-called spin torque effect. The spin-transfer torque (STT) and the field-like spin torque (FLST) are two components of the spin torque effect. We employ the first-principles calculation with the non-equilibrium Green’s function (NEGF) method to analyze the electronic and transport properties. For Fe/MgO/Fe MTJs, the orbital symmetry of ∆_1 state in MgO-barrier is responsible for giant TMR effect that is estimated over 3000% at zero bias. Moreover, our newly developed “JunPy” package is employed to investigate both STT and FLST in non-collinear magnetic configurations, which comparable with previous experimental measurements and theoretical calculations and demonstrate the validity of “JunPy” package. These two components, STT and FLST, are responsible for the magnetization switching, which can control the magnetization configurations in MTJs. As a future work, we propose the EuO-based MTJs and expect the ∆_1 state and spin-polarized EuO-barrier may play a significant role on the enhancement for both TMR and FLST, which may create the next-generation FLST-MRAM.