摻釤釔鐵石榴石薄膜的磁異向性和磁光特性

Abstract

本研究以脈衝雷射沉積法在 YAG (111) 基板上製備 Y3-xSmxFe5O12（0 ≤ x ≤ 3.0）薄膜，系統探討 Sm³⁺ 掺雜對結構、形貌、磁性與磁光性的調控機制。X光繞射結果顯示所有薄膜皆沿 (111) 晶面外延生長；隨x增加，d₄₄₄ 間距按 Vegard 行為單調增大，垂直壓縮應變亦從 −0.74 %（x = 0.5）逐步緩解至 −0.55 %（x ≥ 1.0），並伴隨晶粒尺寸放大。AFM 量測顯示薄膜表面粗糙度均低於 2 nm，顆粒尺寸與X光繞射結果趨勢一致，排除形貌對後續磁光量測的干擾。振動樣品磁力計（VSM）顯示Sm組成為關鍵調控參數： YIG 呈水平磁異向性，而 x ≥ 1.5 時轉為垂直磁異向性，矯頑場與方正度明顯提升；在 x = 2.5 時達最大異向性比≈ 3.0，x = 3.0 則觀測到磁易軸偏離法線約 15° 的現象，顯示高Sm組成下局部結構效應仍具影響。法拉第磁光與磁圓二色光譜均呈Sm3+組成依賴性放大。於 +922 mT 外加磁場下，薄膜在 360 nm 與 440 nm 波段的法拉第旋轉角振幅明顯增強，320–410 nm 區段的積分面積亦隨Sm3+組成增大而提升，正負峰間波長差 Δλ 則趨於收斂。磁圓二色光譜於 275 nm、360 nm 及 440 nm 等波段呈現旋光性放大，並於 x ≈ 1.5 呈現明顯變化，顯示旋光增益與垂直磁化傾向同步增強。綜合結果顯示，Sm³⁺ 掺雜透過調控晶格結構、應變與能帶耦合，可有效強化薄膜於可見至近紫外區段的磁光性能，特別在 360 nm 與 440 nm 波段展現穩定且協同的增益行為，對磁光元件材料設計具重要參考價值。In this study, epitaxial Y3-xSmxFe5O12 (0 ≤ x ≤ 3.0) thin films were fabricated on YAG (111) substrates by pulsed laser deposition to investigate the effects of Sm³⁺ doping on structural, magnetic, and magneto-optical properties. X-ray diffraction analysis confirmed epitaxial growth along the (111) orientation, with lattice spacing expanding and compressive strain gradually relaxing as Sm content increased. The out-of-plane compressive strain is gradually relieved from −0.74% (x = 0.5) to −0.55% (x ≥ 1.0). Atomic force microscopy measurements showed smooth surfaces (roughness< 2 nm), ruling out morphological interference in optical measurements. Magnetic characterization revealed a transition from in-plane magnetic anisotropy in undoped YIG to perpendicular magnetic anisotropy at x ≥ 1.5, with enhanced coercivity and squareness. The maximum anisotropy ratio (~3.0) was observed at x = 2.5, while a slight tilt (~15°) of the easy axis at x = 3.0 indicated structural inhomogeneity effects under high doping. Magneto-optical analyses demonstrated clear doping-dependent enhancements in Faraday rotation and magnetic circular dichroism, particularly at wavelengths of 360 nm and 440 nm. A notable increase in rotation amplitude and a narrowing of peak separation (Δλ) highlighted enhanced magneto-optical coupling.Overall, Sm³⁺ doping effectively tunes lattice structure, strain, and electronic transitions, significantly enhancing magneto-optical performance in the visible to near-UV range, demonstrating potential for magneto-optical device applications.