鏑鐵錳氧鈣鈦礦中之晶格、電子自旋、及電子結構的異向性

Lattice, Spin, and Electronic Anisotropies in DyFe1-x MnxO3 Perovskites

蔣復國(Fu-Kuo Chiang)

指導教授 ： 朱明文 ； 陳福榮

國立清華大學/原子科學院/工程與系統科學系/博士(2011年)

https://doi.org/10.6843/NTHU.2011.00141

摘要

本研究探討了鏑鐵錳氧 (DyFe1-xMnxO3) 鈣鈦礦的晶體結構（斜方晶，空間群定義為 Pbnm）、磁性、以及電子結構，並完成了磁性相圖，其中在錳摻雜含量(X)為 0.5~0.9 的成分中發現了一個還未曾被提出的“磁場引發弱鐵磁”相（field-induced weak ferromagnetism，亦即磁矩方向沿晶格 b 軸為反鐵磁排列，同時向 c 軸傾斜）。在此晶體系統中，隨著錳的添加，由錳離子所誘發的楊-泰勒畸變(Jahn-Teller distortion)會導致晶格沿 bc 面形變並在錳含量大於(含等於) 0.5 時引發有效電子軌域(the effective onset of orbital ordering)的排列；這些晶格特性(同時在電子結構上也被觀察到)，分別由晶格及電子軌域自由度而引起主要在 bc 面上鏑-錳(鐵)間的異向性電子作用以及在 ab 面上的電子異向性，在錳含量為 0.5 時相互競爭，而這些因不同的晶格、電子軌域、以及相關的電子特性所引發的電子基態競爭還有電子異向性間的緊密作用，導致可觀的電子自旋挫折，至終歸結於一沿 a 軸的加洛辛斯基-摩利亞(Dzyaloshinskii-Moriya)作用，與過去所發現的(沿 b 軸)大異其趣，因此可定義並解釋上述”磁場引發弱鐵磁”相的磁矩方向位在 bc 面上。以上這些因子之間的複雜關係在文中將被討論，並且可完滿的解釋此材料系統所呈現的複雜、但未被詳細探討過的磁性相圖。

關鍵字

鈣鈦礦 ； 錳化物 ； 鐵化物 ； 鏑 ； 電子自旋 ； 電子能譜損失

並列摘要

The structural, magnetic properties and electronic structures of the rare-earth perovskites, DyFe1-xMnxO3 (space group, orthorhombic Pbnm), were studied, and the magnetic phase diagram of the solid solution was investigated, which unveiled an unexplored hidden field-induced weak ferromagnetism (antiferromagnetically ordered along b-axis and canted along c-axis) in the material system for x = 0.5~0.9. In the solid solution, the Jahn-Teller distortion contributed by Mn3+ gives rise to the predominance of the bc-plane sublattice with increasing Mn and also the effective onset of orbital ordering in ab-plane for x = 0.5 and above. These distinct features in the respective lattice and orbital degrees of freedom induce the Dy-(Fe,Mn) electronic interaction anisotropy primarily in bc-plane and the growing in(ab)-plane electronic anisotropy, which were simultaneously endorsed by the electronic structures, also effectively competing to each other above x = 0.5. The aroused competition of intrinsic ground states and close entanglement of those anisotropies introduced by the various lattice, orbital, and correlated electronic characters results in considerable spin frustration and eventually the favoring of the Dzyaloshinskii-Moriya interaction dictating along a-axis, in contrast to the conventionally observed b-axis and accounting for the hidden field-induced canted magnetic ordering in bc-plane. The complex interplays of these multiple factors are discussed in the work and satisfactorily explain the rich magnetic phase diagram of the solid solution, which was not investigated in details before.

並列關鍵字

Perovskite ； DyFeMnO3 ； strongly correlated ； structure ； spin ； EELS

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