透過您的圖書館登入
IP:34.231.229.59
  • 學位論文

以第一原理研究Fe/MgO、Co/MgO 和 FeCo/MgO 垂直異相性

First-principle study of the perpendicular magnetic anisotropy in Fe/MgO, Co/MgO and FeCo/MgO

指導教授 : 梁贊全
若您是本文的作者,可授權文章由華藝線上圖書館中協助推廣。

摘要


具有高垂直異相性的磁性材料展現了下一代高密度非揮發記憶體和高熱穩 定性磁紀錄的巨大潛力。實驗證實Ta/FeCoB/MgO/FeCoB/Ta 磁穿隧接 面呈現出高磁晶異相能(MAE)。高磁晶異相性FeCoB/MgO、FeCo/MgO 、Fe/MgO 和Co/MgO 多層的原因已被廣泛的調查。考慮軌道自旋交 互作用力的二階微擾用於各顆原子磁晶異相能的研究。也以態密度分 析,判定Fe/MgO 介面對磁晶異相能的影響。本研究目地在於藉由考 慮軌道自旋交互作用力的一階、二階微擾,調查每顆原子對磁晶異 相能的貢獻。在此微擾的架構下,磁晶異相能可被拆解為原子、軌 道、k 點和能量解析的貢獻。我們實施第一原理密度泛函計算,以調查 Fex/MgO、Cox/MgO、(FeCo)x/MgO 和(CoFe)x/MgO 多層的磁晶異相 能。磁晶異相能的分析是基於微擾理論和佛斯理論(force theorem)。藉由 原子、軌道和能量解析的磁晶異相能貢獻,我們顯示Fex/MgO 磁晶異 相能受到MgO 基板影響的效應。。於Fe/MgO 介面鐵原子的磁晶異相能 增強效應歸因於此軌道躍遷 的影響。隨著磁性層厚 度的增加,在Cox/MgO 的鈷層磁晶異相能增加,而在(FeCo)x/MgO 和 (CoFe)x/MgO 的鈷層磁晶異相能減少。這些磁晶異相能主要來自於磁性層 中心處的原子貢獻。以佛斯理論的運用,我們可描繪兩維布里淵區下k 點 解析的磁晶異相能分布。於Fex 多層,磁晶異相能分布對稱於kx 軸,但在 Fex/MgO 多層,磁晶異相能分布非對稱於kx 軸。總體而言,本文的研究 結果可以增進我們對磁晶異相能物理起因的了解。

並列摘要


Magnetic materials with large perpendicular magnetic anisotropy demon- strate high potential for next-generation high-density non-volatile memories and magnetic recording with high thermal stability. Experiments con firmed that Ta/FeCoB/MgO/FeCoB/Ta perpendicular magnetic tunnel junctions exhibit they have high magnetocrystalline anisotropy energy (MAE). The origin of the high MAEs of FeCoB/MgO, FeCo/MgO, Fe/MgO and Co/MgO multilayers has been widely investigated. The second-order perturbation of spin-orbit interaction was used to study MAE in each atomic site. The density of states was also analyzed to determine the e ffect of the Fe/MgO interface on MAE. This study aims to investigate the MAE contributions in each atom by using the fi rst- and second-order perturbations of the spin- orbit interaction. In the framework of these perturbations, MAE can be de- composed into atomic-, orbital-, k-, and energy-resolved MAE contributions. We performed first-principles density functional calculations to investigate the MAEs of the Fex/MgO, Cox/MgO, (FeCo)x/MgO, and (CoFe)x/MgO multilayers. Analysis of the MAE is based on perturbation theory and force theorem. By using the atomic-, orbital-, and energy-resolved MAE contributions, we demonstrate the e ffect of the MgO substrate on MAE in the Fex/MgO multilayer. The enhancement of MAEs in the interfacial Fe atoms of the Fex/MgO multilayer is attributed to the e ffect of the transi- tion . The MAEs in the Cox and Cox/MgO multilayers increase and those in the (CoFe)x/MgO and (FeCo)x/MgO decrease with increasing thicknesses of magnetic multilayers. These MAEs predominantly arise from atoms in the center region of the magnetic multilayer. With the use of force theorem, we can depict the distribution of k-resolved MAE over the two-dimensional Brillouin zone (2-D BZ). The distributions are sym- metric about the kx-axis in the Fex multilayer, but asymmetric about the kx-axis in the Fex/MgO multilayer. Overall, the findings of this thesis can improve our understanding of the physical origin of MAEs.

參考文獻


[33] Y. F. Wang, W. B. Zhang, Z. Z. Wang, Y. H. Deng, N. Yu, B. Y. Tang, X.
[6] G. Cai, Z. Wu, F. Guo, Y. Wu, H. Li, Q. Liu, M. Fu, T. Chen, and J. Kang,
Nat. Mater. 9, 721{724 (2010).
[2] R. Sbiaa, H. Meng, and S. N. Piramanayagam, Phys. Status Solidi RRL 5,
413{419 (2011).

延伸閱讀