摻鐵釔錳氧化物的磁性研究

Abstract

在本論文研究使用固態燒結法來製備YMn1-xFexO3(x=0, 0.1, 0.2, 0.3)化合物時，其晶體結構與磁性和鐵摻雜的關係。當三價的鐵離子Fe3+摻雜在六方晶系結構的YMnO3中時，摻雜的鐵會取代Mn，由於兩者的離子半徑的不同，摻雜會導致晶格扭曲，最後並造成相轉變。本實驗發現YMnO3六方晶系結構在X >0.2以上時，即有轉變成正交結構的情形，這樣的轉變是受到離子的特性和離子半徑影響。藉由脈衝雷射鍍膜(Pulse Laser Deposition，PLD)的技術，我們在(111)YSZ的基板上成長C軸方向的YMn1-xFexO3(x=0, 0.1, 0.2)薄膜，並使用X光繞射(X-ray diffraction，XRD)與超導量子干涉儀(Superconducting Quantum Interference Device，SQUID)來研究薄膜的晶體結構與磁性，以進一步比較摻雜Fe3+的效應。結果發現Fe3+ 離子在YMn1-xFexO3 (x=0, 0.1, 0.2, 0.3)的粉末中表現出順磁的特性，而在YMn1-xFexO3 (x=0, 0.1, 0.2)薄膜中則是呈現反鐵磁性，顯示基板與薄膜間的應力，可能在材料的磁性作用中，扮演極為關鍵的角色。

The compounds of YMn1-xFexO3 (x=0, 0.1, 0.2, 0.3) studied in this thesis were synthesized by conventional solid state reaction method. The substitution of trivalent cation Fe3+ for Mn in the hexagonal YMnO3 may lead to phase transition when exceeding certain concentration. In this study, we succeed that the hexagonal structure of YMn1-xFexO3 can only sustain to X≦0.2. Such a transition usually depends on the cation nature and ionic radius . Epitaxially c-axis oriented thin films of YMn1-xFexO3 (x = 0,0.1, 0.2) were grown on (111) YSZ substrates by pulsed laser deposition technique .The crystalline structure and magnetic measurement of the compounds were studied to delineate the effect of doped Fe3+. We observe that the magnetic properties of the bulk powders are quite different from that of the films with similar composition ,indicating that the substrate strain may also play an important role. The Fe3+ ion in the YMn1-xFexO3 (x=0, 0.1, 0.2, 0.3) powder exhibits a paramagnetic characteristics while in the YMn1-xFexO3(x=0, 0.1, 0.2) thin films antiferromagnetism was observed.