退火溫度對銩鐵石榴石磁異向性之影響
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2025
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本研究利用脈衝雷射沉積法在 YAG(111) 與 GGG(111) 基板上製備 YIG 與 TmIG 薄膜，並系統性探討退火溫度對其結晶結構、磁性及磁光特性的影響。X光繞射結果顯示，所有薄膜皆沿(111)基板方向異質外延生長，並具有明顯的 (444) 繞射峰。成長於YAG基板的薄膜因高溫退火導致鋁離子進入薄膜，造成晶格收縮及壓縮應變加劇。GGG基板上的樣品則顯示出不同應力表現，YIG樣品中觀察到雙層結構對應拉伸與壓縮應力，而TmIG樣品則為壓縮應力，並隨退火溫度上升逐漸釋放，歸因於Ga³⁺與Fe³⁺半徑相近，使擴散效應微弱。高溫退火主要以應變鬆弛及缺陷修復為主，應變逐步釋放。磁性方面，隨著退火溫度升高，成長於 YAG 與 GGG 基板的 YIG 與 TmIG 薄膜，其飽和磁化量（Ms）均明顯下降，推測主因為高溫退火導致鐵離子向基板擴散，造成磁性離子缺失，進而削弱整體磁性表現。磁易軸方面，YIG/YAG 薄膜的磁易軸由垂直逐漸轉變為無明顯易軸，TmIG/YAG 與 TmIG/GGG 薄膜在各退火條件下皆無明顯磁易軸，而 YIG/GGG 薄膜則始終保持平行磁易軸。矯頑場（Hc）方面，成長於 YAG 基板之薄膜與 TmIG/GGG 薄膜皆隨退火溫度升高而增加，顯示其磁性由軟磁性逐漸轉為硬磁性，唯有 YIG/GGG 薄膜之Hc對退火溫度變化不具明顯趨勢。磁光分析顯示，所有樣品的法拉第旋轉角及磁圓二色性強度均隨退火溫度升高而下降，並觀察到對應O–Fe能階躍遷的吸收峰逐漸消失，佐證了鐵離子擴散現象。綜合而言，退火溫度為影響REIG薄膜結構與磁性的重要關鍵參數。適度退火有助於改善結晶品質及應變釋放，但過高溫度會導致結構劣化及性能下降。本研究結果有助於 REIG 薄膜磁異向性及磁光性能的進一步調控，並為其在自旋電子學與磁光元件之應用提供重要參考。
In this study, yttrium iron garnet (YIG) and thulium iron garnet (TmIG) thin films were fabricated on (111)-oriented YAG and GGG substrates using pulsed laser deposition (PLD). The effects of post-annealing temperature on the films’ crystal structure, magnetic properties, and magneto-optical characteristics were systematically investigated. X-ray diffraction results showed that all films exhibited heteroepitaxial growth along the (111) direction, with distinct (444) diffraction peaks. For films grown on YAG substrates, high-temperature annealing led to the inward diffusion of Al³⁺ ions from the substrate, resulting in lattice contraction and increased compressive strain. In contrast, the GGG-based samples showed different strain behaviors: the YIG films exhibited a bilayer structure corresponding to tensile and compressive stress components, while the TmIG films exhibited compressive strain that gradually relaxed with increasing annealing temperature. This relaxation is attributed to the comparable ionic radii of Ga³⁺ and Fe³⁺, which limits interdiffusion and allows strain release and defect repair to dominate at high temperatures.Magnetic measurements revealed that the saturation magnetization (Ms) of all YIG and TmIG films decreased significantly with increasing annealing temperature, which is attributed to Fe ion diffusion into the substrate and the consequent loss of magnetic ions. Regarding magnetic anisotropy, the YIG/YAG films exhibited a transition from out-of-plane to no clear easy axis; both TmIG/YAG and TmIG/GGG films showed no defined magnetic easy axis under any annealing condition. In contrast, the YIG/GGG films consistently exhibited in-plane magnetic anisotropy. Coercivity (Hc) increased with annealing temperature for YAG-based films and TmIG/GGG films, indicating a transition from soft to hard magnetic behavior. However, YIG/GGG films showed no clear correlation between Hc and annealing temperature.Magneto-optical analysis showed that both the Faraday rotation angle and magnetic circular dichroism (MCD) strength decreased with increasing annealing temperature. Furthermore, the gradual disappearance of absorption peaks corresponding to O–Fe electronic transitions provided additional evidence for Fe ion diffusion.In conclusion, annealing temperature plays a critical role in determining the structural, magnetic, and magneto-optical properties of REIG thin films. While moderate annealing improves crystallinity and strain relaxation, excessive annealing leads to structural degradation and performance deterioration. These findings offer valuable insight for the optimization of REIG thin films and their applications in spintronics and magneto-optical devices.
In this study, yttrium iron garnet (YIG) and thulium iron garnet (TmIG) thin films were fabricated on (111)-oriented YAG and GGG substrates using pulsed laser deposition (PLD). The effects of post-annealing temperature on the films’ crystal structure, magnetic properties, and magneto-optical characteristics were systematically investigated. X-ray diffraction results showed that all films exhibited heteroepitaxial growth along the (111) direction, with distinct (444) diffraction peaks. For films grown on YAG substrates, high-temperature annealing led to the inward diffusion of Al³⁺ ions from the substrate, resulting in lattice contraction and increased compressive strain. In contrast, the GGG-based samples showed different strain behaviors: the YIG films exhibited a bilayer structure corresponding to tensile and compressive stress components, while the TmIG films exhibited compressive strain that gradually relaxed with increasing annealing temperature. This relaxation is attributed to the comparable ionic radii of Ga³⁺ and Fe³⁺, which limits interdiffusion and allows strain release and defect repair to dominate at high temperatures.Magnetic measurements revealed that the saturation magnetization (Ms) of all YIG and TmIG films decreased significantly with increasing annealing temperature, which is attributed to Fe ion diffusion into the substrate and the consequent loss of magnetic ions. Regarding magnetic anisotropy, the YIG/YAG films exhibited a transition from out-of-plane to no clear easy axis; both TmIG/YAG and TmIG/GGG films showed no defined magnetic easy axis under any annealing condition. In contrast, the YIG/GGG films consistently exhibited in-plane magnetic anisotropy. Coercivity (Hc) increased with annealing temperature for YAG-based films and TmIG/GGG films, indicating a transition from soft to hard magnetic behavior. However, YIG/GGG films showed no clear correlation between Hc and annealing temperature.Magneto-optical analysis showed that both the Faraday rotation angle and magnetic circular dichroism (MCD) strength decreased with increasing annealing temperature. Furthermore, the gradual disappearance of absorption peaks corresponding to O–Fe electronic transitions provided additional evidence for Fe ion diffusion.In conclusion, annealing temperature plays a critical role in determining the structural, magnetic, and magneto-optical properties of REIG thin films. While moderate annealing improves crystallinity and strain relaxation, excessive annealing leads to structural degradation and performance deterioration. These findings offer valuable insight for the optimization of REIG thin films and their applications in spintronics and magneto-optical devices.
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脈衝雷射沉積（PLD）, 稀土鐵石榴石（REIG）, 退火溫度, 磁性各向異性, 磁光效應, Pulsed Laser Deposition (PLD), Rare-earth Iron Garnet (REIG), Annealing Temperature, Magnetic Anisotropy, Magneto-optical effect