鎳鐵合金/氧化鎳/鉑之異質結構的自旋轉矩鐵磁共振

Abstract

本研究主要希望能夠增加代表著自旋轉矩-鐵磁共振(spin-torque ferromagnetic resonance, ST-FMR) 中，電荷電流轉換為自旋電流之轉換效率的自旋霍爾角的大小(spin Hall angle, SHA)。我們使用的基本材料為，用於產生自旋轉矩的鉑(Pt)金屬，以及產生鐵磁共振(ferromagnetic resonance, FMR)的鎳鐵合金(permalloy, Py, Ni80Fe20)。為了提升轉換效率，我們嘗試了兩種方法。第一種方法是在原本由Pt (5nm)與Py (5nm)所組成的雙層異質結構之間，再夾入一層2 nm厚的一氧化鎳(NiO)，希望能夠由此使得異質結構的自旋霍爾角增大。另外我們也有將此樣品最低降溫到了1.5 K左右進行量測，也分析了此樣品在各種溫度下的自旋霍爾角大小。第二種方法是將原本作為產生自旋轉矩的Pt，更換為別的材料。在本研究中，我們選用了近期較為熱門的PtTe2作為替代材料，並且實踐出了一整套製程，可以將塊材狀的二維材料，製作成可以量測ST-FMR的樣品。

The primary focus of this study is to enhance the magnitude of the spin Hall angle (SHA), which signifies the charge-to-spin conversion efficiency of spin-torque ferromagnetic resonance (ST-FMR). The foundational materials employed encompass platinum (Pt), employed for generating spin torque, as well as a nickel-iron alloy (permalloy, Py, Ni80Fe20), responsible for inducing ferromagnetic resonance (FMR). To augment the conversion efficiency, two distinct methods were explored.The first method involved inserting a 2 nm thick layer of nickel oxide (NiO) between the bilayer heterostructure composed of Pt (5nm) and Py (5nm). The intention was to amplify the spin Hall angle within this heterostructure. Additionally, we conducted measurements on this specimen at temperatures as low as around 1.5 K and analyzed the magnitude of the spin Hall angle across various temperature ranges.The second method entailed substituting Pt, conventionally used for generating spin torque, with an alternative material. In this study, we opted for the recently popular PtTe2 as the replacement material. We successfully devised an entire fabrication process to transform bulk-like 2D materials into specimens suitable for ST-FMR measurements.