利用同步輻射技術研究不同形貌之矽基板La0.7Sr0.3MnO3/Si對於磁性和錳價態之間交互作用的影響

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Title:	利用同步輻射技術研究不同形貌之矽基板La0.7Sr0.3MnO3/Si對於磁性和錳價態之間交互作用的影響
Other Titles:	Studying interplay between Mn valency and magnetization in Si nanosubstrate-modified La0.7Sr0.3MnO3 thin films by x-ray absorption spectroscopy
Authors:	方楚涵;Fang, Chu-Han
Contributors:	淡江大學物理學系碩士班彭維鋒
Keywords:	鑭鍶錳氧;吸收光譜;X光吸收之圓二向性;LSMO;XANES;EXAFS;XMCD
Date:	2016
Issue Date:	2017-08-24 23:38:01 (UTC+8)
Abstract:	本文主要利用X光光譜探討不同形貌之矽基板對La0.7Sr0.3MnO3/Si的影響。由場效發射式掃描電子顯微鏡 (SEM) 及超導量子干涉儀 (SQUID) 之結果推測樣品晶粒尺寸的變化與其飽和磁化強度以及磁化現象有所關連。進一步藉由錳L3, 2-edge以及氧K-edge近邊吸收光譜得知由氧缺陷所造成的錳二價離子以非等量的形式存在於不同形貌矽基板的常態錳三、四價樣品中。另一方面，由錳L3, 2-edge邊磁圓偏振光譜中發現此錳二價離子會因為含量的不同，產生相異的磁耦合作用。藉由以上量測包含SEM, X光光譜以及磁性相關技術，推斷樣品在不同形貌矽基板中所導致不同的邊界或缺陷效應，會造成錳二價與錳三、四價離子兩者之間的含量比例在不同樣品中的差異。而此含量比例與樣品中飽和磁化強度並非呈現完全的線性關係，這暗示錳二價在樣品中會造成磁性不穩定的狀態，除了降低鐵磁性的效應, 如: 磁死層(magnetic dead layer)之外，尚存在其他影響磁耦合的因子。 This investigation of x-ray spectroscopy is focused on the series samples of La0.7Sr0.3MnO3/n+-Si with different morphology. The results of scanning electron microscope (SEM) and superconducting quantum interference device (SQUID) show that the magnetism is basically associated with the grain size of each sample. The existence of the various amount of Mn2+ between these generally Mn3+/4+-doped samples is observed by Mn L3, 2-edge and O K-edge x-ray absorption near edge structure (XANES). Based on XANES, this amount of Mn2+ is strongly related to the oxygen defect. On the other hand, Mn L3, 2-edge X-ray magnetic circular dichroism (XMCD) was carried out for the magnetic coupling which is sensitive to amount of Mn2+. According to the measurements above including SEM, x-ray and magnetism related techniques, the Si substrates with different morphology cause the change of Mn valence state with more or less amount of Mn2+ in each sample via the various defects or boundary conditions. However, the incompletely linear relationship between ferromagnetism and amount of Mn2+ implies that this amount of Mn2+ induces a magnetically unstable state. Except the reduction of ferromagnetic coupling, e.g. magnetic dead layer (MDL), there are still some other factors left to influence magnetic coupling.
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