Tb1-xEuxMnO3多鐵電及結構相性研究

The magnetic and dielectric phase diagram of Tb1-xEuxMnO3

許憲銓(H.C.Hsu)

指導教授 ： 徐永源

國立臺灣師範大學/理學院/物理學系/碩士(2010年)

摘要

在Tb1-xEuxMnO3的物理特性和磁電相圖中，我們反映了兼具順電及傾斜反鐵磁(Eu)到包含螺旋式磁鐵電有序的多鐵電(Tb)之間在低溫的相變。
在本文中，Tb1-xEuxMnO3 (0 ≤ x ≤ 1, Eu-Tb) 的相圖和之前所報導的Eu1-xYxMnO3 (Eu-Y)和Tb1-xGdxMnO3 (Gd-Tb)的系統皆有鐵電性是經由Dzyalosinski-Moriya (DM) 交互作用發生在複雜電性轉換的極化方向邊界。而Tb1-xEuxMnO3的優勢是近似平均離子半徑包含(Gd-Tb)系統且避免GdMnO3的不確定相；另一方面，穩定且充分研究的TbMnO3在Eu-Tb的系統相較於YMnO3在不穩定的Eu-Y的系統更可提供確切的系統訊息。
Rietveld方法分析說明了求得Mn-O2-Mn鍵角在ab平面隨著x的增加而變大。已觀察到反鐵磁磁有序的Neél溫度大約在44到52 K。介電係數在28 K左右的波峰也說明此溫度以下進入了鐵電相。此外，Tb1-xEuxMnO3 (0 ≤ x ≤ 0.5)的等溫磁滯曲線在所有多鐵電材料中顯示存有似迴圈的異常磁性。此外，為了研究聲子模式隨著不同的Eu濃度在正交多晶晶格Tb1-xEuxMnO3的變化，我們也做了有關拉曼方面的測量。

關鍵字

順電及傾斜反鐵磁 ； 螺旋式磁鐵電有序 ； Rietveld方法 ； 多鐵電

並列摘要

The physical properties and electromagnetic phase diagram of Tb1-xEuxMnO3 (0 ≤ x ≤ 1) system is reported, which undergoes transitions from canted-antiferromagnetic paraelectric state (Eu-side) to spiral-ordered magnetic, ferroelectric state (Tb-side), also known as multiferroic state, at low temperature.
The phase diagrams of Tb1-xEuxMnO3 (0 ≤ x ≤ 1, Eu-Tb) is similar to those reported for , Eu1-xYxMnO3 (Eu-Y) and Tb1-xGdxMnO3 (Gd-Tb) systems in the literatures, whose ferroelectricities are due to Dzyalosinski-Moriya (DM) interaction with complicated polarization re-orientation near the ferroelectric phase boundary. The advantage of the Tb1-xEuxMnO3 system is that the average can cover the Gd-Tb system and avoid the uncertain state of GdMnO3; on the other hand, the stable and well-studied end member TbMnO3 of Eu-Tb system can provide more reliable systematic information than the unstable orthorhombic YMnO3 in Eu-Y system.
The Rietveld refinement analysis indicates that the ab-plain Mn-O2-Mn bond angle increases smoothly as x increases. The observed antiferromagnetic ordering temperature, TN, varies from 44 to 52 K. The dielectric constant ε’(x,T) having peaks around 28 K indicates system enters ferroelectric phase below these temperatures. In addition, the isothermal magnetic hysteresis of Tb1-xEuxMnO3 (0 ≤ x ≤ 0.5) showed anomalous meta-magnetism like loops in all multiferroic samples. In order to investigate the Eu content x dependence of the phonon modes we also employ room temperature Raman scattering on orthorhombic polycrystalline Tb1-xEuxMnO3 (0 ≤ x ≤ 1).

並列關鍵字

canted-antiferromagnetic paraelectric state ； spiral-ordered magnetic, ferroelectric state ； Rietveld method ； multiferroic

參考文獻

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