氫氣影響鐵鈀合金與鎂基多層膜的磁性以及結構變化
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2023
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氫化效應對磁性材料的影響已被廣泛研究，目前已知的熱門儲氫材料中以可在室溫且低氫氣分壓儲氫的鈀(Pd)為主，其高氫敏感性適合觸發材料中的磁性變化。本篇論文以第一部分著重在鎂(Mg)基儲氫材料，其儲氫能力是自身體積4倍最受矚目，然而Mg塊材需要高溫高壓的氫氣環境才能吸收氫氣並且儲存。通過鈀覆蓋層的催化作用，氫分子的裂解在催化過程中有效發生，促進氫原子擴散到底層的純鎂。該過程已被實驗證實在室溫、1 bar的氫氣壓力下發生。Pd/鈷(Co)/Mg多層膜的磁光柯爾效應(MOKE)在真空和1 bar氫氣壓力下測量以進行比較。氫化效應不可逆地將矯頑力(Hc)從25 Oe提高到大約200 Oe。在使用原子力顯微鏡(AFM)量測表面形貌下，氫化後的樣品表面粗糙度從0.1增加到6 nm，且通過 X 射線衍射(XRD)量測在室溫環境下形成穩定的MgH2相。此外，將具有高儲氫穩定性的Mg間隔層夾在Pd/Co/Mg/Fe多層結構中，以提高其儲氫穩定性並探索該結構的磁傳輸特性。透過平面磁場四點測量，磁阻率(MR ratio)的變化從0.22±0.01%增加到0.30±0.01%，這也表明MgH2增加了自旋散射概率和熱效應的穩定性。在我們研究的第二部分，我們重點關注了Pd的獨特性，特別是其高吸氫能力和可逆氫化行為，以及氫氣脫付的遲滯現象，這使其非常適合與氫相關的應用。為了解氫化對磁性的影響，我們的目的是探索氫化對磁異向性能的改變及其與FePd薄膜晶體結構的關係。我們採用X射線磁圓二色性(XMCD)來檢測氫吸收對FePd合金薄膜中Fe磁矩的影響，透過觀察到特徵峰的顯著變化，表明磁性行為發生了變化。值得注意的是，我們發現 FePd薄膜中的磁異向性可以通過吸氫和解吸過程可逆地旋轉無需外部磁場。這使我們能夠實現無磁場開關，這是磁控制領域的一個顯著進步。此外，我們的研究證實FePd薄膜的磁異向性主要受界面應變誘導的磁異向性能與傾斜沉積誘導的表面微結構之間的競爭，且通過橫截面透射電子顯微鏡(TEM)分析和檢查不同厚度的FePd異向能證實了這一觀察結果。總結來說，我們的研究為氫化對磁性薄膜磁性的影響提供了有價值的見解。這些發現證明了MgH2形成、自旋散射和Pd/Mg基多層膜的磁性之間的相關性。 FePd合金體系中磁異向性的可逆控制是通過吸氫和解吸實現。這項研究為自旋電子元件中氫遷移和存儲的控制提供了不同的見解，為磁性元件中的磁矩切換機制引入了新的自由度。
The investigation of hydrogenation-induced effects on magnetism has garnered significant attention due to its promising applications in various fields. Palladium (Pd) is a well-known hydrogen storage material that exhibits high hydrogen uptake capacity at room temperature and under low hydrogen partial pressure conditions. It is widely recognized as one of the most popular materials for hydrogen storage, and high hydrogen sensitivity is suitable to trigger the magnetic change in the material. The initial section of this dissertation is dedicated to exploring hydrogen storage materials based on magnesium (Mg). Mg-based hydrogen storage materials have gained significant attention due to their high hydrogen storage capacity, which is approximately four times their own volume. However, it should be noted that bulk Mg materials necessitate high-temperature and high-pressure conditions to effectively absorb and store hydrogen.Through the catalytic action of the Pd-capping layer, the cleavage of hydrogen molecules effectively occurs in a catalytic process, facilitating the diffusion of hydrogen atoms into the under layer pure Mg. This process has been experimentally confirmed to occur at room temperature (RT) under a hydrogen pressure of 1 bar. The magnetic properties of the Pd/Co/Mg multilayer are analyzed using the hysteresis loop, measured by the magneto-optic Kerr effect (MOKE). A comparison of the magnetism change is performed under two conditions: vacuum state and after exposure to 1 bar of hydrogen gas. The hydrogenation effect significantly increased the coercivity (Hc) from 25 to approximately 200 Oe in an irreversible manner. Additionally, the surface roughness of the sample raised from 0.1 to 6 nm, as observed through an atomic force microscope (AFM). The formation of a stable MgH2 phase was confirmed in an ambient environment at RT through X-ray diffraction (XRD) analysis after the absorption of hydrogen. Moreover, an Mg spacer layer with high hydrogen storage stability was incorporated into a Pd/Co/Mg/Fe multilayer structure to enhance its hydrogen storage stability and investigate the magneto-transport properties of the structure. The magnetoresistance (MR) ratio change increased from 0.22±0.01% to 0.30±0.01% by MR measurement with in-plane magnetic field, which also suggests that MgH2 increased spin scattering probability and stability of thermal effect.In the second part of our study, our focus shifted to the remarkable properties of Pd, specifically its high hydrogen uptake capacity, reversible hydrogenation behavior, and the hysteresis observed during hydrogen desorption. These characteristics make Pd extremely well-suited for applications involving hydrogen. To understand the influence of hydrogenation on magnetic properties, our aim was to explore the effect of hydrogenation on the magnetic anisotropy energy (MAE) and its relationship with the crystalline structure of the FePd films. Additionally, we employed x-ray magnetic circular dichroism (XMCD) to examine the impact of hydrogen absorption on the magnetic moment of Fe in FePd alloy thin films. This technique allowed us to observe significant changes in the characteristic peak, indicative of modifications in the magnetic behavior. Remarkably, we discovered that the magnetic anisotropy (MA) in FePd films could be reversibly rotated through the process of hydrogen absorption and desorption, without the need for an external magnetic field. This enabled us to achieve field-free switching, a notable advancement in the field of magnetism control. Furthermore, our investigation confirmed that the MA of FePd films is primarily governed by the competition between interfacial strain-induced MAE and the surface microstructure induced by oblique deposition. We substantiated this observation through cross-section transmission electron microscope (TEM) analysis and by examining FePd samples with varying thicknesses.Overall, our study provides valuable insights into the influence of hydrogenation on the magnetism of magnetic films. These findings demonstrate the correlation between MgH2 formation, spin scattering, and the magnetic properties of Pd/Mg-based multilayers. The reversible control of MA in the FePd alloy system is achieved through hydrogen absorption and desorption. This study offers different insights into the control of hydrogen migration and storage in spintronic devices, introducing a new degree of freedom in the mechanism of magnetic moment switching in magnetic devices.
The investigation of hydrogenation-induced effects on magnetism has garnered significant attention due to its promising applications in various fields. Palladium (Pd) is a well-known hydrogen storage material that exhibits high hydrogen uptake capacity at room temperature and under low hydrogen partial pressure conditions. It is widely recognized as one of the most popular materials for hydrogen storage, and high hydrogen sensitivity is suitable to trigger the magnetic change in the material. The initial section of this dissertation is dedicated to exploring hydrogen storage materials based on magnesium (Mg). Mg-based hydrogen storage materials have gained significant attention due to their high hydrogen storage capacity, which is approximately four times their own volume. However, it should be noted that bulk Mg materials necessitate high-temperature and high-pressure conditions to effectively absorb and store hydrogen.Through the catalytic action of the Pd-capping layer, the cleavage of hydrogen molecules effectively occurs in a catalytic process, facilitating the diffusion of hydrogen atoms into the under layer pure Mg. This process has been experimentally confirmed to occur at room temperature (RT) under a hydrogen pressure of 1 bar. The magnetic properties of the Pd/Co/Mg multilayer are analyzed using the hysteresis loop, measured by the magneto-optic Kerr effect (MOKE). A comparison of the magnetism change is performed under two conditions: vacuum state and after exposure to 1 bar of hydrogen gas. The hydrogenation effect significantly increased the coercivity (Hc) from 25 to approximately 200 Oe in an irreversible manner. Additionally, the surface roughness of the sample raised from 0.1 to 6 nm, as observed through an atomic force microscope (AFM). The formation of a stable MgH2 phase was confirmed in an ambient environment at RT through X-ray diffraction (XRD) analysis after the absorption of hydrogen. Moreover, an Mg spacer layer with high hydrogen storage stability was incorporated into a Pd/Co/Mg/Fe multilayer structure to enhance its hydrogen storage stability and investigate the magneto-transport properties of the structure. The magnetoresistance (MR) ratio change increased from 0.22±0.01% to 0.30±0.01% by MR measurement with in-plane magnetic field, which also suggests that MgH2 increased spin scattering probability and stability of thermal effect.In the second part of our study, our focus shifted to the remarkable properties of Pd, specifically its high hydrogen uptake capacity, reversible hydrogenation behavior, and the hysteresis observed during hydrogen desorption. These characteristics make Pd extremely well-suited for applications involving hydrogen. To understand the influence of hydrogenation on magnetic properties, our aim was to explore the effect of hydrogenation on the magnetic anisotropy energy (MAE) and its relationship with the crystalline structure of the FePd films. Additionally, we employed x-ray magnetic circular dichroism (XMCD) to examine the impact of hydrogen absorption on the magnetic moment of Fe in FePd alloy thin films. This technique allowed us to observe significant changes in the characteristic peak, indicative of modifications in the magnetic behavior. Remarkably, we discovered that the magnetic anisotropy (MA) in FePd films could be reversibly rotated through the process of hydrogen absorption and desorption, without the need for an external magnetic field. This enabled us to achieve field-free switching, a notable advancement in the field of magnetism control. Furthermore, our investigation confirmed that the MA of FePd films is primarily governed by the competition between interfacial strain-induced MAE and the surface microstructure induced by oblique deposition. We substantiated this observation through cross-section transmission electron microscope (TEM) analysis and by examining FePd samples with varying thicknesses.Overall, our study provides valuable insights into the influence of hydrogenation on the magnetism of magnetic films. These findings demonstrate the correlation between MgH2 formation, spin scattering, and the magnetic properties of Pd/Mg-based multilayers. The reversible control of MA in the FePd alloy system is achieved through hydrogen absorption and desorption. This study offers different insights into the control of hydrogen migration and storage in spintronic devices, introducing a new degree of freedom in the mechanism of magnetic moment switching in magnetic devices.
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氫化效應, 磁性, 自旋散射, 磁異向性, hydrogenation effect, magnetism, spin scattering, magnetic anisotropy