鐠系與鉍系龐磁阻材料結構、電性、磁性間的互動關係研究; Interplay among the structural, transport, and magnetic behaviors in Pr-based and Bi-based CMR material.

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题名:	鐠系與鉍系龐磁阻材料結構、電性、磁性間的互動關係研究;Interplay among the structural, transport, and magnetic behaviors in Pr-based and Bi-based CMR material.
作者:	楊仲準;Chun-Chuen Yang
贡献者:	物理研究所
关键词:	磁有序;磁結構;電荷有序;龐磁阻;中子繞射;CMR;Neutron Scattering;Magnetic ordering;Magnetic structure;Charge ordering
日期:	2004-06-04
上传时间:	2009-09-22 10:54:33 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	Pr0.65Ca0.25Sr0.1MnO3的晶體結構已透過中子與X光繞射實驗分析。在室溫下PCSMO屬於斜方晶系的Pbnm空間群，並且發現在200 K附近發生了楊-泰勒扭曲。在高解析度中子繞射譜圖、比熱、磁化率、與電阻率實驗均發現在190 K時，系統進入的電荷有序態。在此一溫區外加超過2 T的磁場後，系統會進入電荷去局域化態。可能的原因為磁致伸縮效應改變晶體的扭曲程度造成場致CO-CD轉變。溫度低於180 K，Mn原子的磁矩開始形成p-CE型反鐵磁有序。在100 K至80 K間，磁矩發生部分自旋反轉的現象。25 K之下Pr亦呈現發生磁有序。本研究得以獲得磁場對溫度的相圖，呈現Pr0.65Ca0.25Sr0.1MnO3系統的物理特性。室溫下Bi1-xCaxMn0.95Cr0.05O3(x=0.5、0.6)皆為斜方晶系的Pbnm空間群。x=0.5與0.6的樣品分別在285 K與在280 K時發生楊-泰勒扭曲。兩個樣品電阻率的實驗皆可以使用不定域跳躍的電阻率理論：ρVHR=ρ0exp[(T/T0)^1/4]來加以描述。這顯示了BCMCO系統中電子-聲子強烈的耦合。在90 K與80 K時，x=0.5與0.6的樣品分別發生Mn的磁有序。兩樣品磁結構均呈現叢集與鍊狀結構交錯的相分離現象。Cr摻雜破壞Mn-O-Mn的相關性，造成電荷有序態的抑制與Mn磁有序溫度降低。 Crystall structure of Pr0.65Ca0.25Sr0.1MnO3 at room temperature was revealed by using x-ray and neutron diffraction technologies. It crystallized into an orthorombic Pbnm phase at room temperature, and Jahn-Teller distortion was observed at 200 K. All high resolution neutron diffraction experiment, heat capacity, ac susceptibility, and resistivity measurements reveal a charge ordered state at 190 K, which can be transformed into the charge delocalized state by an applied magnetic field of strength larger then 2 T. We believed that it is the magnetostriction effect that transforms the CO state into the CD one. Below 180 K, the Mn moment becomes ordered into the p-CE AFM arrangement. A spin reorientation occurs between 100 K and 80 K. The Pr moments were also found to be ordered at 25 K. We obtained an H-T phase diagram for describing the thermo-magneto properties of Pr0.65Ca0.25Sr0.1MnO3. Both Bi1-xCaxMn0.95Cr0.05O3, with x=0.5 and 0.6 crystallized into an orthorombic Pbnm phase at room temperature. The Jahn-Teller distortion were observed at 285 K and 280 K of the x=0.5 and 0.6 compounds, respectively. The resistivity can be described by variable range hopping mechanism, where ρVHR=ρ0exp[(T/T0)^1/4], indicating a strong electron and phonon coupling for the present BCMCO system. The Mn were orderd at 90 K and 80 K for x=0.5 and 0.6 compounds, respectively. Phase separation, where Mn4+ clusters were surrounded by Mn3+ ions, was revealed in the ordered spin arrangement at low temperatures.
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