氮化及氧化銅覆蓋層對鉑鈷結構的自旋軌道矩性質調整之研究

Abstract

5d軌域的過渡金屬，例如鉑、鉭、鎢等都擁有著很強的自旋霍爾效應，這讓他們成為自旋軌道矩磁阻式隨機存取記憶體的常用材料。相對的屬於3d軌域的銅，本身的自旋霍爾角較弱。透過自然氧化造成的氧化梯度或是在鐵磁層及銅介面的氧化等方式，可以強化其本身造成的類阻尼自旋霍爾矩效率。在這篇文章裡我們改用氮去改變在用於鉑-鈷異質結構上的銅覆蓋層，藉由磁滯曲線平移實驗和電流引發磁化方向翻轉實驗，我們可以觀察到氮化銅在鉑-鈷-氮化銅(氧化銅)具有和氧化銅一樣的強化效果。在製備樣品時控制氮氣或氧氣流量，可使鈷-氮化銅介面產生一個與鉑-鈷同號的強自旋軌道矩。在此同時，不同於鉑-鈷-氧化鎂及鎢-鈷鐵硼-氧化鎂結構，鉑-鈷-氮化銅結構展現出可用於類神經系統相關的可調控穩定多態表現。

The 5d transition metals, like Pt, Ta, W, posses strong spin Hall effect, which are good choices for spin-orbit torque type magnetic random access memory as spin current sources. On the contrary, Cu, a light metal, has a weak spin Hall effect. There are several ways to enhance its damping-like spin-orbit torque (SOT) efficiency, for example, the oxidation gradient caused by natural oxidation or interface oxidation. Here we use nitrogen instead, probing that CuNx have the same enhancement behavior as CuOx in Pt/Co/CuNx (CuOx) heterostructures through hysteresis loop-shift measurement and current-induced switching measurement. By controlling the nitrogen and oxygen concentration in Cu layer, the interface of Co/CuNx (CuOx) generates a strong spin-orbit coupling, which has the same sign of Pt/Co. At the same time, Pt/Co/CuNx shows a neuromorphic-like multi-states behavior, which is very different from Pt/Co/MgO and W/CoFeB/MgO heterostructures.