標題: 以時間解析光譜研究鑭鍶錳氧/鐵酸鉍異質結構之各向異性超快動力學
Anisotropic Ultrafast Dynamics in La0.67Sr0.33MnO3 /BiFeO3 Heterostructure Studied by Time-Resolved Spectroscopy
作者: 羅晟
Luo, Cheng
羅志偉
Luo, Chih-Wei
電子物理系所
關鍵字: 鑭鍶錳氧/鐵酸鉍;各向異性;超快動力學;金屬絕緣相變;紅外反射光譜;小極化子;相分離;La0.67Sr0.33MnO3 /BiFeO3;Anisotropy;Ultrafast Dynamics;Metal-Insulator Transition;Infrared Reflectance Spectrum;Small Polaron;Phase Separation
公開日期: 2013
摘要: 在本論文中,我們用光學的方法探討由BiFeO3所操控之La0.67Sr0.33MnO3 的各向異性。此樣品的兩軸向([001]、[1-10])的電阻值有很大差異,並且有不同的金屬─絕緣轉變溫度。從紅外光譜我們觀察到小極化子吸收峰,證明BiFeO3使La0.67Sr0.33MnO3電子的雙交換機制增強。並且從變溫紅外光譜可知,載子濃度隨溫度降低會逐漸增加,在160 K以下達到飽和,與[1-10]的金屬─絕緣轉變溫度相符。我們也利用時間解析的反射光譜研究各向異性,在低溫下,光譜有一個明顯的負值訊號,我們推論來源是La0.67Sr0.33MnO3鐵磁的訊號。並且我們得到電子自旋─晶格的弛緩時間(~100 ps)和磁有序的回復時間(~ns)對溫度的關係。從趨勢上可以知道兩軸向的電子自旋─晶格的弛緩時間在其金屬─絕緣相變溫度會有斜率的轉折。而磁有序的回復時間也在此溫度點以上發散以致無法量測。綜合以上各點,我們觀察到兩軸磁的各向異性。
In this thesis, we discuss the anisotropy of La0.67Sr0.33MnO3 manipulated by BiFeO3 by optical method. There is a large difference in resistance along two axises([001],[1-10]), and two metal-insulator transition temperatures(TMI). By IR reflectance spectrum, We observe small polaron absorption in La0.67Sr0.33MnO3 which is upon BiFeO3. It proves that BiFeO3 enhances the double-exchange mechanism between electrons of La0.67Sr0.33MnO3. We also observe carrier concentration increase with lowering temperature, and saturate below 160 K. It matches TMI along [1-10]. We also use time-resolved reflectance spectroscopy to investigate anisotropy. At low temperature, it appears a negative component, and we demonstrate this is from ferromagnetism of La0.67Sr0.33MnO3. By fitting, we obtain temperature dependent spin-lattice relaxation time(~100 ps) and magnetic reordering time(~ ns). For spin-lattice relaxation time, there exists sharp change at TMI in slope. For magnetic reordering time, it also diverges at TMI. In conclusion, it presents the magnetic anisotropy along two axises.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT070052014
http://hdl.handle.net/11536/73978
Appears in Collections:Thesis