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題名 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
作者 吳明璟
Wu, Ming Ching
貢獻者 郭光宇
Guo, Guang Yu
吳明璟
Wu, Ming Ching
關鍵詞 磁性異向性
磁性穿隧結
自旋電子學
穿隧磁阻
Magnetic anisotropy
Magnetic tunnel junction
Spintronics
Tunnel magnetoresistance
日期 2013
上傳時間 1-Oct-2014 13:15:41 (UTC+8)
摘要 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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2. M. Julliere “Tunneling between ferromagnetic films.” Physics Letters A 54(3): 225-226(1975).
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4. J. S. Moodera, L. R. Kinder, T. M. Wong, and R. Meservey “Large Magnetoresistance at Room Temperature in Ferromagnetic Thin Film Tunnel Junctions”. Phys. Rev. Lett. 74 (16): 3273–3276 (1995).
5. S. S. P. Parkin, C. Kaiser, A. Panchula, P.M Rice, B. Hughes ,M. Samant ,S.H. Yang “Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers”. Nat. Mat. 3 (12): 862–867(2004).
6. W. H. Butler, X.G. Zhang, T. C. Schulthess, and J. M. MacLaren “Spin-dependent tunneling conductance of Fe/MgO/Fe sandwiches”. Phys. Rev. B 63 (5): 054416.J (2001).
7. J. Mathon and A. Umerski “Theory of tunneling magnetoresistance of an epitaxial Fe/MgO/Fe (001) junction”. Phys. Rev. B 63 (22): 220403(2001).
8. S. Yuasa, T. Nagahama, A. Fukushima, Y. Suzuki, and K. Ando “Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions”. Nat. Mat. 3 (12): 868–871(2004).
9. H. X. Yang, J. H. Lee, M. Chshiev, A. Manchon, K. H. Shin, B. Dieny “First-principles investigation of the very large perpendicular magnetic anisotropy at Fe|MgO and Co|MgO interfaces” Phys. Rev. B 84, 054401 (2011)
10. J.M.D. Teresa, A. Barthélémy, A. Fert, J.P. Contour, F. Montaigne, P. Seneor” Role of Metal-Oxide Interface in Determining the Spin Polarization of Magnetic Tunnel Junctions” Science 286 no. 5439 pp. 507-509 (1999)
11. P. M. Tedrow and R. Meservey (1971). “Direct Observation of Spin-State Mixing in Superconductors.” Physical Review Letters 27(14): 919-921.
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13. S. Ikeda, J. Hayakawa, Y. Ashizawa, Y.M. Lee, K. Miura, H. Hasegawa, M. Tsunoda, F. Matsukura and H. Ohno “Tunnel magnetoresistance of 604% at 300 K by suppression of Ta diffusion in CoFeB/MgO/CoFeB pseudo-spin-valves annealed at high temperature” Appl. Phys. Lett. 93, 082508 (2008).
14. P.W.T. Pong, and W. F. Egelhoff “Enhancement of Tunneling Magnetoresistance by Optimization of Capping Layer Thicknesses in CoFeB/MgO/CoFeB Magnetic Tunnel Junctions”. Appl. Phys, vol. 105, 07C915 (2009)
15. J. V. Vleck, “Theory of the Variations in Paramagnetic Anisotropy Among Different Salts of the Iron Group”. Physical Review 41: 208 (1932).
16. X.G. Zhang, W. H. Butler “Large magnetoresistance in bcc Co/MgO/Co and FeCo/MgO/FeCo tunneling junctions” Phys. Rev. B 70, 172407 (2004)
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27. T. Moriyama, C. Wang, W.G Zhang, X. Xiao, Q. John, “Tunneling magnetoresistance in (001)-oriented FeCo/MgO/FeCo magnetic tunneling junctions grown by sputtering deposition” Appl. Phys. Lett. 88, 222503 (2006)
28. S. Yuasa and D. Djayaprawira, “Giant tunnel magnetoresistance in magnetic tunnel junctions with a crystalline MgO(001) barrier”J. Phys. D: Appl. Phys. 40, R337(2007).
29. S. Ikeda, J. Hayakawa, Y. M. Lee, F. Matsukura, and H. Ohno “Dependence of tunnel magnetoresistance on ferromagnetic electrode materials in MgO-barrier magnetic tunnel junctions”, J. Magn. Magn. Matter., vol. 310(2007)
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32. U. Bauer, M. Dabrowski, M. Przybylski, and J. Kirschner,” Experimental confirmation of quantum oscillations of magnetic anisotropy in Co/Cu(001)”Phys. Rev. B84, 144433 (2011).
33. H. Kubota, S. Ishibashi, T. Saruya, T. Nozaki, A. Fukushima, K. Yakushiji, K. Ando, Y. Suzuki, and S. Yuasa , “Enhancement of perpendicular magnetic anisotropy in FeB free layers using a thin MgO cap layer”Appl. Phys 111, 07C723 (2012)
34. D.S. Wang, R. Wu, and A. J. Freeman, “First-principles theory of surface magnetocrystalline anisotropy and the diatomic-pair model” Phys. Rev. B47, 14932(1993).
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36. P. Bruno,” Tight-binding approach to the orbital magnetic moment and magnetocrystalline anisotropy of transition-metal monolayers” Phys. Rev. B 39, 865(1989)
37. P. V. Ong, N. Kioussis, P. K. Amiri, J. G Alzate, K. L. Wang, G. P. Carman, J. Hu, and R. Wu “Electric field control and effect of Pd capping on magnetocrystalline anisotropy in FePd thin films: A first-principles study” Phys. Rev. B 89, 094422 (2014)
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40. G. C. Fletcher, “Calculations of the First Ferromagnetic Anisotropy Coefficient, Gyromagnetic Ratio and Spectroscopic Splitting Factor for Nickel” Proc. Phys. Soc. London, Sect. A 67, 505 (1954)
41. T. I Cheng, C. W Cheng, G. Chern” Perpendicular magnetic anisotropy induced by a cap layer in ultrathin MgO/CoFeB/Nb” Appl. Phys. Lett. 112, 033910 (2012)
描述 碩士
國立政治大學
應用物理研究所
100755015
102
資料來源 http://thesis.lib.nccu.edu.tw/record/#G1007550154
資料類型 thesis
dc.contributor.advisor 郭光宇zh_TW
dc.contributor.advisor Guo, Guang Yuen_US
dc.contributor.author (Authors) 吳明璟zh_TW
dc.contributor.author (Authors) Wu, Ming Chingen_US
dc.creator (作者) 吳明璟zh_TW
dc.creator (作者) Wu, Ming Chingen_US
dc.date (日期) 2013en_US
dc.date.accessioned 1-Oct-2014 13:15:41 (UTC+8)-
dc.date.available 1-Oct-2014 13:15:41 (UTC+8)-
dc.date.issued (上傳時間) 1-Oct-2014 13:15:41 (UTC+8)-
dc.identifier (Other Identifiers) G1007550154en_US
dc.identifier.uri (URI) http://nccur.lib.nccu.edu.tw/handle/140.119/70249-
dc.description (描述) 碩士zh_TW
dc.description (描述) 國立政治大學zh_TW
dc.description (描述) 應用物理研究所zh_TW
dc.description (描述) 100755015zh_TW
dc.description (描述) 102zh_TW
dc.description.abstract (摘要) 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。zh_TW
dc.description.abstract (摘要) 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.en_US
dc.description.tableofcontents 摘要．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．3
表目錄．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．6
圖目錄．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．9
1. 緒論．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．14
1.1 穿隧磁阻及磁電阻式隨機存取記憶．．．．．．．．．．．．．．．14
1.2 金屬氧化物多層膜的磁性隧道結．．．．．．．．．．．．．．．．16
2. 理論背景．．．．．．．．．．．．．．．．．．．．．．．．．．．．18
2.1 Jullier 模型．．．．．．．．．．．．．．．．．．．．．．．．．18
2.2 Butler模型．．．．．．．．．．．．．．．．．．．．．．．．．19
3. 能帶理論與計算方法．．．．．．．．．．．．．．．．．．．．．．．21
3.1 何謂第一原理．．．．．．．．．．．．．．．．．．．．．．．21
3.2 由密度泛函理論解釋量子多體問題．．．．．．．．．．．．．．22
3.3 Born-Oppenheimer近似．．．．．．．．．．．．．．．．．．．23
3.4 Hohenberg-Kohn原理．．．．．．．．．．．．．．．．．．．．23
3.5 Kohn-Sham方程式．．．．．．．．．．．．．．．．．．．．．25
3.6 交換關聯泛函之近似．．．．．．．．．．．．．．．．．．．．27
3.7 解晶體電子本微方程．．．．．．．．．．．．．．．．．．．．28
4. 超薄鐵磁氧化物多層薄膜中的穿隧磁阻．．．．．．．．．．．．．．．30
4.1 結構模型．．．．．．．．．．．．．．．．．．．．．．．．．．30
4.1.1 氧化鎂、鐵、鐵鉑合金的晶體結構．．．．．．．．．．．．．30
4.1.2 超晶胞及超晶格結構模擬．．．．．．．．．．．．．．．．．35
4.2 電子結構及磁矩．．．．．．．．．．．．．．．．．．．．．．．39
4.2.1 自旋極化率和穿隧磁阻比．．．．．．．．．．．．．．．．．45
4.3 鉭及氧化鎂覆蓋層對鐵氧化鎂多層膜的影響．．．．．．．．．．．51
4.3.1 不同元素種類覆蓋層影響．．．．．．．．．．．．．．．．．51
4.3.2 覆蓋層厚度差異影響．．．．．．．．．．．．．．．．．．56
5. 超薄鐵磁氧化物多層薄膜中的磁性異向性．．．．．．．．．．．．．57
5.1 結構模型．．．．．．．．．．．．．．．．．．．．．．．．．57
5.1.1 超晶胞及超晶格結構模擬．．．．．．．．．．．．．．．．57
5.1.2 氧化鎂、鐵和鐵鉑晶體結構．．．．．．．．．．．．．．．57
5.2 電子結構和軌道磁矩．．．．．．．．．．．．．．．．．．．．58
5.2.1 軌道磁矩及磁晶異向性．．．．．．．．．．．．．．．．．66
5.3 鉭及氧化鎂覆蓋層對鐵氧化鎂多層膜的影響．．．．．．．．．．71
6. 討論與結果．．．．．．．．．．．．．．．．．．．．．．．．．．86
7. 參考文獻．．．．．．．．．．．．．．．．．．．．．．．．．．．87		zh_TW
dc.language.iso en_US-
dc.source.uri (資料來源) http://thesis.lib.nccu.edu.tw/record/#G1007550154en_US
dc.subject (關鍵詞) 磁性異向性zh_TW
dc.subject (關鍵詞) 磁性穿隧結zh_TW
dc.subject (關鍵詞) 自旋電子學zh_TW
dc.subject (關鍵詞) 穿隧磁阻zh_TW
dc.subject (關鍵詞) Magnetic anisotropyen_US
dc.subject (關鍵詞) Magnetic tunnel junctionen_US
dc.subject (關鍵詞) Spintronicsen_US
dc.subject (關鍵詞) Tunnel magnetoresistanceen_US
dc.title (題名) 第一原理理論計算研究鐵(鐵鉑)/氧化鎂薄膜和介面的磁性zh_TW
dc.title (題名) Ab Initio Studies of the Magnetic Properties of Fe(FePt)/MgO Thin Films and Interfacesen_US
dc.type (資料類型) thesisen
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