Ab Initio Studies of the Magnetic Properties of Fe(FePt)/MgO Thin Films and Interfaces

• Main Authors: Wu, Ming Ching, 吳明璟
• Other Authors: Guo, Guang Yu
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/98531767546984584292

碩士 === 國立政治大學 === 應用物理研究所 === 102 === People have found that electron transportation is effected by spin affection in magnetic materials in recent year. This phenomenon was used generally in magneto resistive random-access memory. In this thesis, we use first-principle method to calculate physical characteristics of magnetic tunnel junction such as band structure. We simulate multi-thin film structure, especially for MgO barrier. We use iron or FePt as ferromagnetic layer with barrier for supercell structure. We also calculate for superlattice Ta or MgO capping on ferromagnetic at Fe/MgO structure with vacancy. We use Jullier model to calculate Tunnel magneto resistance ratio by analyzing density of state at Fermi level result. We found that in Fe/MgO structure, when ferromagnetic layer number increase, tunnel magnetoresistance ratio will decrease. In FePt/MgO structure, iron oxide terminate configuration have larger tunnel magnetoresistance than platinum oxygen terminate. In superlative with capping structure, tantalum element capping will reduce ferromagnetic polarization. Therefore, the magnetic tunnel junction structure with tantalum capping configuration tunnel magnetoresistance is less than MgO capping configuration. For perpendicular magnetic anisotropy energy calculation, spin–orbit coupling will be considered. The band structure shows the affection of different orbital. We calculate magnetic anisotropy energy with spin-orbit coupling consider, which magnetization direction lies in-plane and out of plane in Fe/MgO structure. There has an band split at Γ point, which shows that Γ point might be the direction occur perpendicular magnetic anisotropy energy. Beside, MgO and ferromagnetic layer interface layer iron has high ratio of dxz and dyz orbital density of state at Fermi level. Consequently, these two orbital plays an important role in spin–orbit interaction. In supercell configuration calculation, we found tantalum element will decrease ferromagnetic orbital moment near interface of capping layer and ferromagnetic layer. Accordingly, MgO capping has larger perpendicular magnetic anisotropy energy than tantalum capping. In FePt/MgO structure, platinum oxygen terminate configuration has larger perpendicular magnetic anisotropy energy than iron oxygen terminate configuration.