手性(chiral)磁性是很特別的物理性質，例如自旋冰/液體磁序、拓樸絕緣體和磁電偶..等，都與其有所關聯。而這些獨特的現象中，最讓人感興趣的地方在於存在著不尋常的自旋排列。
　　而本篇研究的主要樣品Cu2OSeO3本身就是為手性磁結構，而且還具有很特別的磁矩螺旋排列稱為skyrmion。而Cu2OSeO3在溫度56K左右時具有亞鐵磁性，而當增添適度的外加磁場，會從螺旋態(helical state)經過中間的skyrmion phase到達錐形態(conical state)。我們主要在研究等價離子的摻雜效應對Cu2OSeO3中skyrmion現象會有什麼影響，利用固態合成法製作多晶樣品(Cu1-xNix)2OSeO3 (x = 0.0 ~ 0.1)，並進行一連串的磁性研究。
　　磁性方面，從ac -T的量測中發現隨著鎳摻雜比例的提升，轉變溫度朝低溫偏移，且注意到鎳摻雜比例超過0.03時，有第2個尖峰的產生。之後從M-H的量測中，隨著鎳摻雜比例提升強度沒明顯的改變，我們推測出Cu¬(I)和Cu(II)兩個位置，鎳都會進行取代。最後進行一系列的不同溫度下χ´ac-H的量測，我們畫出一系列的相圖，並進行比較，發現幾個明顯的改變。首先觀察到在T = 45 K時Conical state的邊界有些微增加，從806.22 Oe (x = 0) 變成 996.42 Oe (x = 0.1)，而Helical state邊界值隨著摻雜增加有一些減少。最令人感興趣的是skyrmion系統受到Ni強烈的影響，隨著摻雜的增加直到x = 0.06，都有系統的讓skyrmion區域增大。當摻雜濃度超過x = 0.08時發現具有分裂的現象。從我們實驗結果發現磁性離子對Cu2OSeO3的Cu(I)和Cu(II)形成強大的磁性交互作用，從相圖中也可以看到對skyrmion相產生影響。

Chiral magnetic lattice shows exotic physical properties such as spin ice/spin liquid order, topological insulators, magneto-electric coupling, and so on. Essentially, all these fascinating phenomena have strongly related to their peculiar spin arrangement, i.e. spiral, conical and helical. The chiral magnetic lattice of Cu2OSeO3 exhibit such kind of unique magnetic ordering where spins configured into a vortex-like pattern called as skyrmion. Cu2OSeO3 exhibits ferrimagnetic ordering around 56 K. Below magnetic ordering, under moderate magnetic field the spin orientation transfer from helical to conical phase via intermediate skyrmions phase. In this thesis, we study the influence of isovalent doping on the Skyrmion phase of Cu2OSeO3.
The polycrystalline (Cu1-XNiX)2OSeO3 (x = 0.0 to 0.1) samples were prepared by standard solid-state method. Temperature (T) and field (H) dependent AC susceptibility (ac) technique was employed to study the H-T phase diagram. From ac vs. T measurement, we found the transition temperature (TC) shifts to low temperature as the Ni doping level increases. A second magnetic peak noticed below TC for doping concentration x > 0.03. Field dependent magnetization (M-H) curves indicate the nominal change of saturation magnetization, which hints the Ni randomly occupy the Cu(I) and Cu(II) positions. H-T phase diagram for all the samples constructed using the ac vs. H curves at the different temperatures. Several significant changes noticed from the H-T phase diagram. First, the conical phase boundary enhances from 806.22 Oe (x = 0) to 996.42 Oe (x = 0.1) at 45 K, whereas small decrease in helical boundary noticed with increase of Ni doping concentration. Interestingly, Ni doping strongly influence the skyrmion zone, the skyrmion zone systematically enhances with the doping concentration x = 0.06. For x ≥ 0.08, a split in the skyrmion zone has been noticed. Our detailed experimental results signifies that the magnetic ion doping in the Cu2OSeO3 strongly modulate the complex magnetic interaction of Cu(I) and Cu(II) that stabilize the skyrmion phase in wider temperature interval in the H-T phase diagram.

論文審定書+i
論文公開授權書+iii
致謝+iv
論文摘要+v
Abstract+vi
目錄+viii
圖目錄+x
表目錄+xiii
第一章:簡介+1
1-1 Skyrmion+1
1-2 Cu2OSeO3簡介+7
1-3研究動機+15
第二章:實驗儀器與方法+17
2-1 粉末繞射分析儀D2 Phaser+17
2-2 磁性量測儀器+19
2-2-1 超導量子干涉磁量儀+19
2-2-2 磁性量測方法+22
第三章:實驗結果與討論+24
3-1 (Cu1-xNix)2OSeO¬3，x = 0 to 0.1樣品製備+24
3-2 (Cu1-xNix)2OSeO¬3，x = 0 to 0.1 X-ray結構分析+26
3-3 磁性實驗結果與討論+35
第四章:結論+55
參考文獻+57

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