摻雜銩元素的釔鐵石榴石結構與磁性探討

Abstract

本研究利用脈衝雷射沉積法，在 GGG(111) 和 YAG(111) 基板上生長摻雜銩元素的釔鐵石榴石(TmYIG)薄膜，並探討在室溫下的結構、表面形貌、磁性和磁光特性。膜厚由表面輪廓儀測量，鍍膜靶材鍍率具有沉積時間和薄膜厚度的線性關係，代表鍍膜速率為定值。薄膜結構由X 射線繞射測量，光譜顯示在 GGG(111)呈現雙層結構，薄膜的應變從壓縮轉為拉伸，其中唯一拉伸應變佔據主導性的薄膜是TmIG。此雙層結構中具拉伸應變的薄膜靠近GGG基板，壓縮應變的薄膜則在最上層。在YAG(111)基板上的薄膜晶格常數(lattice constant)則隨著 Tm 含量的增加而減小。YAG(111)基板上的TmYIG薄膜皆表現出壓縮應變。AFM 量測結果間接證實TmYIG/GGG具有雙層結構，而且以層狀+島狀的形式生長；TmYIG/YAG則以島狀的形式生長。VSM的檢測發現磊晶於兩種基板上的TmYIG薄膜在平行與垂直磁場下的矯頑場都會隨著Tm 摻雜量的增加而增大，從0 Oe增大到150 Oe。方正度則表明隨著Tm含量增加磁矩趨向法線方向，TmIG/GGG唯一具有垂直磁異向性(PMA)，代表TmIG/GGG具有拉伸應變與XRD結果中TmIG惟一由拉伸應變主導的薄膜相符。TmYIG薄膜的磁光法拉第效應在波長 300 和 500 nm 之間最強。飽和法拉第旋轉角在 2 到 24 mrad 之間，其中在 GGG(111) 上生長的薄膜具有稍大的飽和法拉第旋轉角。磁性和磁光檢測表明只有 TmIG/GGG 表現出可能的PMA，與VSM的結果相同。In this study, TmxY3-xFe5O12 (TmYIG) thin films were grown on GGG(111) and YAG(111) substrates by pulsed laser deposition. Structural, surface topography, magnetic and magneto-optical properties are measured at room temperature. The film thickness is measured by a profilometer, and a linear relationship between the deposition time and the film thickness is observed, that the thin film deposition rate is a constant value. The film structure is measured by X-ray diffraction. The spectra shows that TmYIG/GGG(111) thin film have a double-layer structure. The only film has dominant tensile strain is TmIG. In addition, the film peak which has tensile strain is on the GGG substrate, and the film which has compressive strain is at the top. The lattice constant of the film on the YAG(111) substrate decreases with the increase of Tm content. TmYIG films on YAG(111) substrates all exhibit compressive strain. AFM measurements indirectly confirmed that TmYIG/GGG has a double-layer structure and grows in the form of layers + islands, while TmYIG/YAG grows in the form of islands. VSM found that the coercivity of the TmYIG film epitaxial on the two substrates under in plane and out plane will increase with the increase of the Tm content, from 0 to 150 Oe. The squareness indicates that as the Tm content increases, the magnetic moment tends to the normal direction, and TmIG/GGG is the only has perpendicular magnetic anisotropy. This means that TmIG/GGG has tensile strain. It matches that TmIG is the only film of dominat tensile strain in XRD results. The magneto-optical Faraday effect of TmYIG thin films is strongest between the wavelengths of 300 and 500 nm. The saturated Faraday rotation angles range from 2 to 24 mrad, with films grown on GGG(111) having slightly larger saturated Faraday rotation angles. Magnetic and magneto-optical examinations indicated that only TmIG/GGG exhibited a possible PMA, identical to the results of VSM.