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    Please use this identifier to cite or link to this item: http://nccur.lib.nccu.edu.tw/handle/140.119/70249

    Title: 第一原理理論計算研究鐵(鐵鉑)/氧化鎂薄膜和介面的磁性
    Ab Initio Studies of the Magnetic Properties of Fe(FePt)/MgO Thin Films and Interfaces
    Authors: 吳明璟
    Wu, Ming Ching
    Contributors: 郭光宇
    Guo, Guang Yu
    Wu, Ming Ching
    Keywords: 磁性異向性
    Magnetic anisotropy
    Magnetic tunnel junction
    Tunnel magnetoresistance
    Date: 2013
    Issue Date: 2014-10-01 13:15:41 (UTC+8)
    Abstract: 近年來人們發現電子在不同磁性材料上會受自旋影響而改變傳導性質,此現象可應用在磁電阻式隨機存取記憶。因此本論文利用第一原理計算磁性穿隧通道結構的磁矩、電子結構、磁性異向能(MAE)等等。特別是以鐵(Fe)及鐵鉑合金(FePt)為鐵磁層,氧化鎂(MgO)為阻障層之超晶格結構以及增加氧化鎂或鉭(Ta)為覆蓋層具真空層之超晶胞。我們利用Jullier 模型透過電子態密度,計算穿隧磁阻比(TMR),我們發現在Fe/MgO/Fe穿隧結的結構增加鐵磁層數會使穿隧磁阻比下降,在FePt/MgO/FePt穿隧結的結構中鐵氧接面比鉑氧接面型態擁有高穿隧磁阻比值,在有覆蓋層型態上鉭覆蓋層會使鐵極化率減弱,進而使鉭覆蓋層的穿隧磁阻比值比氧化鎂覆蓋層小。垂直磁性異向能方面,我們引入自旋軌道交互作用計算不同自旋方向模式分析軌道磁矩,最後分解能帶以分析軌域對磁性異向能的影響。我們發現在Fe/MgO結構的自旋方向在垂直於平面與平行於平面兩種形態時,Γ點附近會因為自旋軌道交互作用發生分裂現象,這說明在Γ點附近可能是造成垂直磁性異向能之發生原因,並且氧化鎂接面鐵的dxz和 dyz軌域在費米能級附近擁有高比例之電子密度分布,這代表dxz和 dyz軌域在自旋軌道作用中扮演中要角色。在有覆蓋層結構計算中,我們也發現坦覆蓋層會減弱鉭與鐵磁層接面附近鐵的軌道磁矩,因此氧化鎂覆蓋層結構的垂直磁性異向能高於坦覆蓋層結構,而在我們計算FePt/MgO結構中鉑氧接面型態結構的垂直磁性異向能高於鐵氧接面結構垂直磁性異向能。
    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.
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    Description: 碩士
    Source URI: http://thesis.lib.nccu.edu.tw/record/#G1007550154
    Data Type: thesis
    Appears in Collections:[應用物理研究所 ] 學位論文

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