鈀基薄膜受氫化誘導無場磁自旋翻轉

Abstract

隨著低功耗自旋電子器件對精準磁矩控制的需求，無磁場驅動的可逆磁化旋轉充滿潛力；其透過簡單的切換即可在室溫下快速改寫磁易軸方向，為新一代磁阻式感測器、氫感測元件與 SOT-MRAM 提供極具潛力的致動機制。研究以氫化誘發磁矩無場翻轉為核心，系統探討 Pd 基薄膜之磁性、電性與電子結構調變機制。首先，採共蒸鍍方式將 Fe₄₀Pd₆₀ 以 45° 斜鍍沉積於 c-plane 藍寶石基板，因為陰影效應在表面形成一維波紋，使其產生單一方向對稱的磁晶異向性，以及與基板不匹配而生的介面異向性的競爭態勢。MOKE 量測顯示，一般情況下磁晶異向性主導，氫化後易軸旋轉約 70°，磁滯曲線由方正轉為傾斜，證實出現氫化驅動的自旋再對齊轉變（SRT）。藉由對薄膜逐層蝕刻可知，隨厚度降低磁晶異向性 貢獻遞減，而氫化仍可使易軸最終鎖定於 90°，突顯體積磁晶異向性對翻轉的主導角色。磁阻與電阻實驗進一步揭示，氫化後磁阻振幅與靈敏度皆顯著提升；磁化翻轉角度與磁疇動力學共同決定曲線形貌。X-ray 吸收光譜指出，氫原子佔據 Pd間隙造成晶格膨脹與 Pd-4d-H-1s 強雜化，使 Pd 端 XANES 肩峰對氫最為敏感，對應電子態密度及鍵結能量之重組。另一方面，本研究亦製備 Pd/Co/Mg 與 Pd/Co/Mg/Fe 多層膜。Co 層厚度由 1–3 nm 時，氫化可將矯頑力由 5 Oe 提升至 226 Oe，且呈現不可逆飽和行為；AFM 與 XRD 佐證鈀裂解氫後產生表面孔洞，驗證 Pd 具室溫催化活性，對磁阻元件有磁性減弱與矯頑力降低的影響，印證氫化對多層耦合的調控潛力。綜上，氫化可同時透過晶格-電子耦合與磁異向性競爭，在 Pd-基薄膜實現可逆且低功耗的磁矩無場翻轉與磁阻調變；其機制清楚連結巨觀磁阻、微觀磁疇與電子結構變化，為氫控制自旋電子元件提供新的材料設計途徑與物理依據。Field-free, reversible magnetization rotation driven by hydrogen absorption offers an energy-efficient route toward precise spin control in next-generation magnetoresistive sensors, H₂ detectors, and SOT-MRAM. Here we systematically elucidate how hydrogenation modulates the magnetism and electronic structure of Pd-based thin films.Fe40Pd60 layers were co-evaporated at a 45° oblique angle onto c-plane sapphire. Shadow effect induced one-dimensional surface ripples generate a uniaxial magnetocrystalline anisotropy(K1) that competes with interface anisotropy(K2) originating from lattice mismatch. MOKE measurements show that, under ambient conditions, the K1 term dominates; after hydrogen uptake the easy axis rotates by ≈ 70°, and the square hysteresis loop becomes slanted, evidencing a hydrogen-driven spin-reorientation transition. Depth-selective ion-etching reveals that thinning the film suppresses the K1 contribution, yet hydrogen still locks the easy axis to 90°, underscoring the key role of volume anisotropy in the final rotation.Magnetoresistance and resistivity experiments demonstrate pronounced enhancements in MR amplitude and sensitivity upon hydrogenation; the curve shape is jointly governed by the rotation angle and domain-wall kinetics. XAS indicates that H atoms occupy octahedral interstices of the Pd lattice, producing lattice expansion and strong Pd-4d–H-1s hybridization. The Pd K-edge XANES shoulder, highly sensitive to hydrogen, reflects the reconstructed DOS and bonding energies.To extend the concept, Pd/Co/Mg and Pd/Co/Mg/Fe multilayers were fabricated. For Co thicknesses of 1–3 nm, hydrogenation increases the coercive field from 5 Oe to 226 Oe and induces irreversible saturation. AFM and XRD reveal hydrogen-generated surface voids, corroborating Pd’s room-temperature catalytic activity and highlighting how hydrogen tunes interlayer coupling, magnetization and MR performance.Collectively, our results show that lattice–electron coupling and anisotropy competition enable low-power, reversible, field-free magnetization switching and MR modulation in Pd-based films. The clear links among macroscopic MR, microscopic domain behavior and electronic-structure evolution provide a solid physical foundation and design guidelines for hydrogen-controlled spintronic devices.