多磁體RMnO3 (R=Ho, Er, Tm, Yb, Lu and Y)的物性研究

The study on the physical properties of multiferroic RMnO3 (R=Ho, Er, Tm, Yb, Lu and Y)

林美君(Mei-Chung Lin)

指導教授 ： 林昭吟 ； 陳政弦

國立臺灣大學/理學院/物理研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.02668

摘要

在固態反應合成下，稀土錳氧化物RMnO3 ( R = 稀土元素或釔 )依據R3+ 離子半徑的大小可形成二種晶體結構，分別為：（1）當R為半徑較大的La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy時，則會形成正方結構的RMnO3；（2）當R為半徑較小的Ho、Er、Tm、Yb、Lu、Y，則會形成六方結構的RMnO3。這個研究利用固態反應法備製了一系列六方結構的RMnO3（R = Ho、Er、Tm、Yb、Lu、Y）的樣品，藉由X光繞射儀斷定其結構，繼而測量其磁性、電性和比熱的特性，探討不同R3+離子對於整個化合物的物性影響。
研究發現，在磁性的數據中顯示，只有在YMnO3、YbMnO3和LuMnO3清楚出現了反鐵磁的轉變溫度，分別為73 K、87 K和83 K；而由比熱的量測發現，磁性轉變溫度清楚的反應在比熱的性質中，由比熱的轉變溫度可以歸納出，轉變溫度隨R的離子半徑變小而增高。在介電常數的量測中，發現在所有磁轉變溫度附近都出現不正常的轉折現象，證實磁和電性的強關聯性。综而言之，我們的這個研究提供了重要的實驗數據，有助於未來多磁體的理論發展。

關鍵字

多磁體 ； 稀釷氧化物 ； 六角柱

並列摘要

The rare earth manganites RMnO3 (R = rare earth element or Y) exhibit strong magnetic exchange interactions between the magnetic moments of the Mn3+ ions as well as some of the magnetic R3+. Depending on the size of rare earth ion, RMnO3 crystallizes into two different structures：（1） orthorhombic phase for R = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, or Dy which has a larger ionic radius compared with that of Ho；and （2）hexagonal phase for R = Ho, Er, Tm, Yb, Lu or Y which possesses a smaller ionic radius. In this work, we have prepared a series of hexagonal RMnO3 with R = Ho, Er, Tm, Yb, Lu and Y and employed the techniques of X-ray powder diffraction, magnetic susceptibility, heat capacity and dielectric permeability in order to systematically study their R-dependent structural, magnetic and electric properties.
In the data of magnetic susceptibility of these six samples, only YMnO3, YbMnO3 and LuMnO3 show antiferromagnetic transitions near 73 K, 87 K and 83 K respectively. However, the magnetic transition temperatures of all samples are clearly observed in the data of specific heat. It is found that the transition temperature increases with decreasing the radius of R-ion, which is attributed to the enhancement of exchange interaction between Mn3+-ions. In the data of temperature dependent dielectric permeability vs. temperature, anomalies appear near TN in all samples, implying a strong coupling between ferroelectric and magnetic orders in the hexagonal RMnO3 compounds. The results of this study provide important information for the future development of theoretical model for multiferroism.

並列關鍵字

multiferroic ； RMnO3 ； hexagonal

參考文獻

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