透過摻雜提升鉑合金的自旋軌道扭矩效率以降低切換電流密度

Abstract

5d過渡金屬鉑因其強烈的自旋霍爾效應，在自旋軌道扭矩裝置中發揮了關鍵作用。然而，與具有-0.3阻尼類自旋霍爾效率（ξDL）的鎢相比，鉑的ξDL僅約為0.1，使其在實際應用中相對不利。除了具備較高的類阻尼效率外，鉑合金還具有更低的電阻率和更大的可調性（ρxx = 48.0~215.4 μΩ·cm），相較於鎢更具優勢。透過摻雜技術，鉑合金在與鎢相當的電阻率下可以達到更高的類阻尼效率（ξDL = 0.618）。例如，Pt0.8MgO0.2表現出低臨界SOT驅動切換電流密度Jc0 = 1.85 x 10^10 A·m–2。在本研究中，我們探索了多種摻雜元素，包括氧化物（氧化鎳 (ξDL= 0.410)、氧化鎂 (ξDL = 0.618)）、5d過渡金屬（鉭 (ξDL = 0.374)、鎢 (ξDL = 0.284)）、鐵磁材料（鈷 (ξDL = 0.071)、鈷鐵硼 (ξDL = 0.276)）及4d過渡金屬（鈮 (ξDL = 0.457)）。研究結果顯示，摻雜MgO氧化物最能有效提升整體類阻尼效率，並透過特定的薄膜結構設計實現無場切換，同時顯著降低切換電流密度。

The 5d transition metal platinum (Pt) plays a crucial role in spin-orbit torque (SOT) devices due to its strong spin Hall effect. However, compared to tungsten (W), which has a damping-like spin Hall efficiency (ξDL) of -0.3, the ξDL of Pt is only around 0.1, making it less favorable for practical applications. In addition to its high DL efficiency, Pt alloys offers lower resistivity and greater tunability (ρxx = 48.0~215.4 μΩ·cm) compared to W. By utilizing doping techniques, Pt alloys can achieve higher DL efficiency (ξDL = 0.618) even at resistivity levels comparable to W. A low critical SOT-driven switching current density of Jc0 ≈ 1.85 × 1010 A·m–2 is also demonstrated for Pt0.8MgO0.2. In this work, we explored various dopants, including oxides (NiO (ξDL= 0.410), MgO (ξDL = 0.618)), 5d transition metals (Ta (ξDL = 0.374), W (ξDL = 0.284)), ferromagnetic materials (Co (ξDL = 0.071), CoFeB (ξDL = 0.276)), and 4d transition metals (Nb (ξDL = 0.457)). Our findings indicate that doping with MgO oxide most effectively enhances the overall damping-like efficiency and facilitates field-free switching through specific thin-film structure designs, while also significantly reducing the switching current density.