電子掺雜對層狀不相稱的鈷氧化物Ca3-xYxCo4O9 物理性質之影響

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Title:	電子掺雜對層狀不相稱的鈷氧化物Ca3-xYxCo4O9 物理性質之影響
Other Titles:	Effect of electron doping on physical properties of misfit-layered cobaltite Ca3-xYxCo4O9
Authors:	潘俊傑;Pan, Jiun-jie
Contributors:	淡江大學物理學系碩士班林大欽;Ling, Dah-chin
Keywords:	磁電傳輸;強關聯費米液體;自旋密度波;鐵磁的關聯性;陶鐵磁性;spin-density-wave;ferromagneticcorrelation;ferrimagnetism
Date:	2006
Issue Date:	2010-01-11 02:21:25 (UTC+8)
Abstract:	我們詳細地研究了層狀不相稱的鈷氧化物Ca3-xYxCo4O9 (CYCO) 的物理性質。CYCO系統的電阻率隨著Y摻雜量的增加單調地遞增，意味著系統中的電洞濃度隨著Y3+對Ca2+部份取代的增加而遞減。在 T ~ Tmin 附近，電阻率有一個極小值。當T > Tmin, 電阻率呈現金屬的行為，同時遵循T2一直到 T，對於 x = 0, T ~ 170 K；x = 0.2, T* ~ 230 K，這明確地告訴我們CYCO在金屬態時是一個強關聯的費米液體。相對地，當T < Tmin, 電阻率呈現半導體的行為；值得注意的是Tmin隨著Y摻雜量的增加從62 K單調地遞增至120 K。更有趣的是與自旋密度波能隙相關的量dln(R)/d(1/T)在相對應的溫度出現一平台，同時dln(R)/d(1/T)的數值亦隨著Y摻雜量的增加而增加，這說明Tmin 與自旋密度波起始溫度成正比，並且Y摻雜量的增加伴隨著自旋密度波起始溫度的升高。另外，dln(R)/d(1/T)在與陶鐵磁性相關的溫度20 K附近開始隨溫度的降低逐漸遞減，意味著陶鐵磁性的出現對於自旋密度波的能隙有抑制的作用，這個現象在磁場下的dln(R)/d(1/T)對溫度關係圖中很清楚地表現出來。從磁傳輸性質隨Y摻雜量變化的關係來看，我們發現Y摻雜所引發的化學壓力與鈷價數的變化對於[Ca2CoO3] 與 [CoO2] 子系統之間的耦合有深遠的影響，進而導致系統中自旋密度波與陶鐵磁性的消長。 Physical properties of misfit-layered cobaltite Ca3-xYxCo4O9 (CYCO) with polycrystalline samples have been extensively investigated. Electrical resistivity of the Y-substituted sample monotonically increases with increasing Y content, which could be attributed to the decrease of the hole concentration by substitution of trivalent Y3+ for divalent Ca2+. The resistivity exhibits a broad minimum around T = Tmin. At T > Tmin, follows T2 dependence up to T* ~ 170 K for x = 0 and 230 K for x = 0.2 samples, indicating that CYCO is a strongly correlated Fermi liquid in metal state. Whereas T < Tmin, exhibits insulating-like behavior, ranging from 62 K with x = 0 up to 120 K with x = 0.2. The dln(R)/d(1/T), related to the energy gap of SDW, reveals a plateaus and increases with increasing Y content. It suggests that Tmin scales with the onset temperature of SDW and SDW is enhanced by the Y doping. Furthermore, the dln(R)/d(1/T) gradually decreases below a temperature T**, increasing with increasing field for x , at which ferrimagnetism sets in. The variation of interlayer coupling between the [Ca2CoO3] and [CoO2] subsystems caused by substitution-induced chemical pressure as well as valence state change of cobalt has profound influence on the correlated evolution of SDW and ferrimagnetism.
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