鎢鉑鈷鉑異質結構中自旋軌道矩轉換效率之研究

Study of Spin-Orbit Torque Efficiencies in W/Pt/Co/Pt Heterostructures

陳宗奕(Tsung-Yi Chen)

指導教授 ： 白奇峰

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202000315

摘要

先進自旋軌道轉矩式記憶體(SOT-MRAM)具有於兼容性CMOS產業中縮放之優勢，且被視為新世代記憶體的候選人之一。自旋軌道轉矩式記憶體之要點基於自旋軌道矩，其促成由非磁金屬及鐵磁金屬結合之磁性異質結構中鐵磁層的決定性翻轉。為了使用自旋軌道矩，5d過渡金屬(如鉑、鎢、鉭(Pt, W, Ta)等)之自旋傳輸性質被系統性調查，由於其顯著的自旋霍爾效應(SHE)，其亦為自旋軌道矩的來源。在本論文中，我們致力於表徵阻尼似自旋軌道矩(DL-SOT)之行為，其性質從負演進至正於鎢鉑鈷鉑(W/Pt/Co/Pt)異質結構中。電致磁滯曲線偏移量測及電致磁化翻轉量測被利用於確認我們試片之阻尼似自旋軌道矩轉換效率。我們釐清一個具有零轉換效率之元件確實表現出沒有電致磁化翻轉的現象。透過考慮自旋擴散理論(spin diffusion theory)，我們提出一個改良模型其可描述複雜多層膜性統之阻尼似自旋軌道矩行為，並且獲得鉑和鎢之阻尼似自旋軌道矩轉換效率($xi^ ext{Pt}_ ext{Bulk}$ = 0.12, $xi^ ext{W}_ ext{Bulk}$ = -0.13)。在磁滯曲線偏移量測中，我們也注意到特定樣品之Dzyaloshiskii-Moriya交互作用(DMI)呈現出一個異常大的數值。此外，在比較性樣品中所呈現的相似行為意味著放置一個複合膜層於上方並不會造成額外的效應。總結本論文，我們關於鎢鉑鈷鉑之系統性研究表現出可調控之阻尼似自旋軌道矩、恰當之熱穩定性及製備完即具備的垂直磁異向性，此即展現出其應用潛力於自旋軌道轉矩式記憶體。

關鍵字

自旋軌道矩 ； 垂直磁異向性 ； 自旋霍爾效應 ； 對抗自旋流 ； Dzyaloshiskii-Moriya交互作用 ； 電致磁化翻轉

並列摘要

Advanced spin-orbit torque (SOT) magnetic random access memory (MRAM) takes advantage of scaling in compatible CMOS industry and is regarded as the next-generation memory. The essentials of SOT-MRAM based on the SOT, which can assist the deterministic switching of the ferromagnetic metal (FM) layer in a combined magnetic heterostructure of nonmagnetic metal (NM) and FM. To utilize the SOT, 5d transition metals (Pt, W, Ta, etc.) are systematically investigated on the spin transport properties due to their significant spin Hall effect (SHE), which is the origin of SOT. In this thesis, we aim to characterize the damping like (DL)-SOT behavior, which evolves from negative sign to positive sign, in W/Pt/Co/Pt heterostructures. The current-induced hysteresis loop shift measurement and current-induced magnetization switching measurement are utilized to determine the DL-SOT efficiency in our samples. We clarify that a sample with zero DL-SOT efficiency indeed shows no sign of current switching. By considering spin diffusion theory, we suggest a modifying model for describing the DL-SOT behavior in the complex multilayer system and obtaining DL-SOT efficiency of Pt and W ($xi^ ext{Pt}_ ext{Bulk}$ = 0.12, $xi^ ext{W}_ ext{Bulk}$ = -0.13). With the loop shift measurement, we also notice that the Dzyaloshinskii-Moriya interaction (DMI) in specific samples perform an anomalously large value. Furthermore, similar behavior of comparative samples suggests that placing the composite layer on the top is nearly no additional effect. In summary, a systematically study of W/Pt/Co/Pt shows the potential of application on the SOT-MRAM system with tunable DL-SOT behavior, suitable thermal stability, and perpendicular magnetic anisotropy (PMA), which exists as deposited.

並列關鍵字

spin-orbit-torque ； perpendicular magnetic anisotropy ； spin Hall effect ； countering spin current ； Dzyaloshinskii-Moriya interaction ； current-induced magnetization switching

參考文獻

[1] R. C. O’handley, Modern magnetic materials: principles and applications. Wiley, 2000.

[2] C.-Z. Chang and M. Li, “Quantum anomalous hall effect in time-reversal-symmetry breaking topological insulators,” Journal of Physics: Condensed Matter, vol. 28, no. 12, p. 123002, 2016.

[3] N. Nagaosa, J. Sinova, S. Onoda, A. H. MacDonald, and N. P. Ong, “Anomalous hall effect,” Reviews of modern physics, vol. 82, no. 2, p. 1539, 2010.

[4] B. Dieny, R. B. Goldfarb, and K.-J. Lee, Introduction to magnetic random-access memory. John Wiley & Sons, 2016.

[5] D. C. Ralph and M. D. Stiles, “Spin transfer torques,” Journal of Magnetism and Magnetic Materials, vol. 320, no. 7, pp. 1190–1216, 2008.