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    Title: 三角晶格反鐵磁石CuCr1 : xO2 (0≤x≤0.1) 物理性質的研究
    Other Titles: An investigation of physical properties of triangular lattice antiferromagnets CuCr1 : xO2 (0≤x≤0.1)
    Authors: 江昌文;Chiang, Chang-wen
    Contributors: 淡江大學物理學系碩士班
    林大欽
    Keywords: 銅鐵礦;磁性頓挫;磁電效應;delafossite;magnetic frustration;ME (magnetoelectric) effect
    Date: 2010
    Issue Date: 2010-09-23 16:05:12 (UTC+8)
    Abstract: 我們利用固態反應法製作了CuCr1-xO2 (0≤x≤0.1) 的多晶塊材樣品
    ,並且有系統對其作了結構、電性、磁性、熱電性質與介電性質的量測。從X-ray精算分析結果發現,Cr含量減少造成Cu-O鍵長變短,這意味著Cu的3d 電子軌域與O的 2p 電子軌域重疊增加,因此樣品電阻率隨著Cr 含量減少而降低。從吸收譜與磁性量測數據可知,隨著Cr含量減少,樣品中Cr離子仍為三價,部分的Cu離子由Cu+ 轉變成Cu2+
    ,這代表摻雜電洞在Cu的位置上。此外可以發現樣品的磁轉變溫度皆維持在26 K附近,這顯示Cr缺少誘發的電洞與二維CrO2三角晶格中Cr3+ 的局域化自旋,兩者間沒有很密切的關係。由熱傳導率數據可發現,隨著Cr含量減少,樣品的載子數目變多,且樣品的 Seebeck 係數皆為正數,這證實了樣品多數傳導載子為電洞。由探討介電性質可以發現,因磁結構相變造成溫度在低於 23.5 K 後,樣品具有強烈的磁電耦合。隨著 Cr 含量減少,樣品晶格缺陷影響了 Cr 離子自旋受挫程度,而改變系統的磁電耦合強度,導致樣品的物理性質受到影響。從電性傳導機制彌合結果與介電常數隨溫度與磁場變化的數據可發現,CuCr1-xO2 (0≤x≤0.1) 樣品的物理性質以x = 0.04為分界分成兩類。
    We have investigated the structural, magnetic, transport, thermoelectric, and dielectric properties of polycrystalline delafossite oxides, CuCr1-xO2 (0≤x≤0.1). The Cu-O bond distance decreases with decreasing Cr content. The shorter Cu-O bond distance results in the increase in the overlapping integral between Cu 3d and O 2p orbitals. Because of the increase in the overlapping
    integral between the electronic orbitals caused by the topological reason and the increase in the number of hole carriers in the Cu site, the decrease Cr content samples exhibited a lower resistivity than the parent compound CuCrO2. In contrast, the Néel temperature (TN ~ 26 K) of parent compound CuCrO2 is very robust, indicating that the doped holes and the antiferromagnetically coupled local spin of Cr3+ in the two-dimensional CrO2 triangular lattice are not intimately correlated. The deduced effective moment, monotonically decreasing with an decrease of Cr content, is in good agreement with theoretical value based upon the presence of a mixture state of Cu+/Cu2+, suggesting that the doped holes are at the Cu site. Based on thermal conductivity data, we found that the carrier quantities increased with Cr decreasing. Moreover, the Seebeck coefficients of sample are always positive. Thus, it showed us that majority carriers are holes in our samples. That is to say, the sample is p-type semiconductor. After we observe the dielectric properties, there are obvious electromagnetic coupling effect in our samples at the T < 23.5 K caused by magnetic phase transition. With decreasing Cr, the crystal defect will affect the spin frustration of Cr ions. Therefore, the intensity of electromagnetic coupling will be changed. It will result in different physical characteristics. According to the result of the transport mechanism and the data of dielectric constant, we found that the sample CuCr1-xO2 (0≤x≤0.1) can be divided into two types by x=0.04.
    Appears in Collections:[物理學系暨研究所] 學位論文

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