相對於傳統電子元件只利用正負電荷之傳輸特性來進行操作，自旋電子元件如磁性隨機存取記憶體(MRAM)或量子計算則利用電子本身的上自旋、下自旋之特性來控制元件，此種方式具備非揮發性、高速運算、高密度及低耗能的優勢。其中主要的概念是利用自旋轉移力矩(STT)或自旋軌道偶合力矩(SOT)中的電子自旋流來進行高速的磁性翻轉。
以目前來說，STT-MRAM的製程技術相對較為成熟，然而其結構有讀寫共用同一通道的問題，此種方式較易造成讀寫判讀出現問題，且消耗能量也較大。反之，隨著強自旋軌道偶合的材料(如:重金屬、拓樸絕緣體、二為材料等)相繼被發現以及研究，SOT的使用原理也跟著崛起，同時SOT-MRAM具備快速且低耗能的優勢，再者，其讀寫通道可被分開，因此較不會有判讀出現誤差的現象。而在白金/鈷/白金薄膜結構中，白金/鈷介面能夠形成垂直於膜面的磁矩(垂直異向性)，且白金具有強自旋軌道偶合的特性，因此當電流經過後，能夠經由自旋霍爾效應產生垂直於電流方向的自旋流。因為上述兩種原因，此種薄膜結構成為研究SOT-MRAM的對象之一。在本論文中，我們在其結構中分別嵌入銅和鎢，試圖增強其垂直異向性和電子-自旋流的轉換效率。
製程方面，所有薄膜皆在真空1.8E-4 torr下，利用離子束濺鍍法進行成長。量測部分，則利用原子力顯微鏡和電子穿隧顯微鏡來分析其表面和整體結構特性。同時也利用X光繞射與反射來確認晶體結構及薄膜厚度。磁性性質使用磁光柯爾效應、超導量子干涉儀來進行鑑定。電性量測則在黃光製成之後進行異常霍爾效應和自旋軌道偶合力矩之量測，並推算出其自旋霍爾角度。

Compared to traditional devices using electron’s charge properties, spintronics devices aim to utilize the spin degree freedom of electrons for potential applications such as magnetic random access memory (MRAM) or quantum computing which have several significant advantages, including non-volatility, faster data processing speed, higher integration densities, and lower power consumption. One of the main concepts of spintronics is that the spin current can also be viewed as the transfer of angular momentum, which could be used for magnetization switching applications via spin transfer torque (STT) or spin orbit torque (SOT).
Spin transfer torque magnetic RAM (STT-MRAM), a well establish two terminal magnetic tunneling junction (MTJ) technology combined with spin transfer torque writing scheme, is one of the most promising magnetic devices that could allow the large integration of memory and logic cells for more efficient computer system 1, 2. Nevertheless, two short comings that limits the reliability of that technique are: i) high current density is required for writing (switching), which could occasionally damage the MTJ barrier (insulator) ; ii) since write and read share the same path (via the junction), it is still remains a challenge to fulfill a reliable reading.
One the other hand, spin orbit torque (SOT) MRAM emerges due to the discovery of high spin orbit materials (such as heavy elements Pt, β-Ta, β-W or topological insulator etc.). SOT-MRAM requests three terminal design, where the writing and reading paths are separated that can be the efficient way to avoid the damage of the tunneling barrier and the reading problem (e.g. undesired writing while reading). Additionally, owing to the high charge-to-spin conversion feature, low writing current can be anticipated. In comparison to STT MRAM (slow switching times due to the precessional switching), fast-SOT switching is already demonstrated in the experiments 3, showing great potential of SOT MRAM for the low power consumption computing with high performance. As a results , the major challenge is how to improve the conversion efficiency between pure spin current and charge current, which is known as the spin hall angle (θSH).
Recently, a potential candidate for SOT MRAM, the magnetic thin-film multilayer structure Pt/Co/Pt has been intensively investigated owing to its strong spin orbit coupling (SOC) of Pt, which can generate pure spin current due to the spin Hall effect (SHE) and its perpendicular magnetic anisotropy (PMA) between Pt/Co interface. Here, we demonstrate three different structures Pt/Co/Pt, Pt/Co/Cu/Pt and Pt/Co/W/Pt, which all show perpendicular magnetic anisotropy (PMA).
Cu was inserted as a barrier layer between Co/Pt interface due to the immiscibility of Co and Cu. 4 Cu could also prevent the interdiffusion at upper Co/Pt interface which is believed to decrease the PMA density. For the Pt/Co/W/Pt samples, we expected an enhancement of the Slonczewski-like (damping-like) torque will be observed by placing dissimilar metals with opposite spin Hall angles (θ_SH^Pt~0.07 ; θ_SH^(β-W)~ -0.3 ) on opposite sides of the ferromagnet. All the samples were established by ion beam sputter (IBS) under pressure 1.8E-4 torr with 5sccm Ar flow, we also used atomic force microscopy (AFM) and transmission electrons microscopy (TEM) to characterize surface roughness and clean interface of the samples, respectively. Crystalline of β-W and the thickness of Pt, Co, Cu, W were determined by X-Ray diffraction (XRD) and X-Ray reflection(XRR) with Cu Kα source (λ=1.54184À). Interdiffusion between different interfaces were observed by energy dispersive X-ray spectroscopy (EDS). Perpendicular magnetic anisotropy (PMA) were confirmed by magneto-optic Kerr effect (MOKE) and superconducting quantum interfere device (SQUID) at room temperature. For electric properties, thin films were patterned into 8μm* 40μm hall bars after using lithography and ICP reactive-ion etching, followed by a second lithographic step to deposit Cu(70nm)/Pt(5nm) for the electrodes before lift-off. Anomalous Hall effect and current-induced DL-SOT switching was measured.

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