鑭鈣錳氧-鎳鐵氧奈米複合結構鐵磁性薄膜顯微結構與物理性質

Abstract

本論文是以X光繞射分析儀(X-ray diffractometry, XRD)、穿透式電子顯微鏡(Transmission electron microscopy, TEM)，導電原子力顯微鏡(Conductive atomic force microscopy, C-AFM)，物理性質量測系統(Physical property measurement system, PPMS)，震動樣品磁度儀(Vibrating sample magnetometer, VSM)，X光磁圓偏振二向性(X-ray magnetic circular dichroism, XMCD)，與光電子激發顯微鏡(X-ray photoemission electron microscopy, X-PEEM)探討退火製程對鑭鈣錳氧(La0.67Ca0.33MnO3，LCMO)-鎳鐵氧(NiFe2O4,NFO)奈米複合結構鐵磁性薄膜顯微結構與物理性質之影響。 此磁性薄膜是以脈衝雷射沉積於(001)單晶鍶鈦氧(SrTiO3，STO)基板上。利用兩相結構不互溶所引發的自組裝(self-assemble)特性，使得具尖晶石(spinel)結構的NFO與具鈣鈦礦(perovskite)結構的LCMO相分離，又因兩相結構表面能差異進而得到以LCMO為基底，內嵌NFO奈米結構之鐵磁性複合結構薄膜。經由XRD、C-AFM和TEM觀察結果確定，退火製程（1100℃,12小時）有助於LCMO和NFO兩相確實分離，且提高相結構之結晶性。此外，PPMS、VSM和XMCD的結果分別指出，退火使得薄膜的室溫片電阻降低約50%；室溫磁化率提高約100%。 綜合以上結果可知，透過適當薄膜成長與退火製程可改善此類奈米結構元件之顯微結構，進而有效地提昇其物理性質。本論文對於LCMO-NFO元件之開發與物理性質分析結果，將有助於未來以LCMO為基底的奈米結構元件的相關研究。

In this research, we use x-ray diffractometry, transmission electron microscopy, conductive atomic force microscopy, physical property measurement system, vibrating sample magnetometer, x-ray magnetic circular dichroism, and x-ray photoemission electron microscopy to investigate La0.67Ca0.33MnO3(LCMO) -NiFe2O4(NFO) microscopy and physical property of magnetic thin film by annealing process. The film is deposited on SrTiO3(001) by pulsed laser deposition. Two phases self-assemble character makes NFO, which is spinel structure, and LCMO, which is peroskite structure, phase separation. Also, the difference of surface energy between NFO and LCMO makes LCMO matrix and NFO inlaid nanostructure. From XRD, C-AFM, and TEM, annealing process is able to improve two phase complete separation and crystallization. Besides, PPMS, VSM, and XMCD figure out that by annealing process, resistance at room temperature decreases about 50% and magnetization at room temperature increases about 100%. From above-mentioned results, using adequate thin film growth and annealing process could improve microstructure of nanostructure device. And then improve the physical properties efficiently. The result of developing LCMO-NFO device and analyzing physical properties of this study will help researches about nanostructure device which LCMO is matrix in the future.