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Special magnetic phenomena in heavily doped La_(0.7-x)Dy_xSr_(0.3)MnO_3 system

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science china(Physics,Mechanics & Astronomy) 2008年第1期51卷 90-97页

作者： LIU Ning 1,2 ,YAN GuoQing 1,3 ,CAI ZhiRang 1 ,PI Li 2 ,ZHANG Bei 2 &TONG Wei 2 1 Department of Physics,Suzhou College,Suzhou 234000,china 2 structure research laboratory,university of science and technology of china,hefei 230026,china 3 National laboratory of Solid State Microstructures,Physics Department,Nanjing university,Nanjing 210093,china 1. Department of Physics Suzhou College Suzhou 234000 China 2. structure research laboratory University of Science and Technology of China Hefei 230026 China 3. National laboratory of Solid State Microstructures Physics Department Nanjing University Nanjing 210093 China

The magnetism in heavily Dy doped La0.7-xDyxSr0.3MnO3(0.40≤x≤0.70)system is studied in this *** M-T relation seems to be complicated with the increase of *** sample with x=0.40,AFM behavior exists at T≤TN and M-T curves under zero field cooling(ZFC)and field cooling(FC)exhibit typical behavior of spincluster glass state above *** the sample with x=0.50,the M-T curve under ZFC exhibits a valley at a low temperature while the M-T curve under FC exhibits the negative magnetization below *** samples with x=0.60,0.70,their ZFC M-T curves are similar to that of x=0.50,but the FC M-T curves do not exhibit negative values any *** the peculiar phenomena above are well explained by Néel double-lattice model combined with M-H relation at typical *** molecular field theory fits well the negative magnetization for x=0.50.

关键词： heavily doped special magnetic phenomena double-lattice model

research on charge ordering and magnetic properties in La_(0.3)Ca_(0.7)Mn_(1-x)W_xO_3 system

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Rare Metals 2007年第4期26卷 317-322页

作者： PENG Zhensheng GUO Huanyin YAN Guoqing MAO Qiang Physics Department Suzhou College Suzhou 234000 China structure research laboratory University of Science and Technology of China Hefei 230026 China

The perovskite manganite sample La0.3Ca0.7Mn1-xWxO3 （x = 0.08, 0.12） was prepared by the solid-state reaction method. The effect of W doping on the Mn site to La0.3Ca0.7MnO3 charge ordering phase and the changing process of magnetic properties were studied through the measurement of the M-T curve, M-H curves, and ESR curves of the sample. The results showed that when x = 0.08, the charge ordering （CO） phase exists in the system, the transition temperature Tco= 275 K, and the system exhibits PM when T 〉 275 K. The system transforms from spin-disordering paramagnetism to spin-ordering antiferromagnetism in the charge ordering state with the temperature decreasing from 275 K to 230 K. The long-range antiferromagnetism forms and AFM/CO states coexist between 230 K and 5 K. There is a little ferromagnetic component in the AFM/CO background in a low temperature range. When x = 0.12, the CO phase in the system has almost melted completely. There is a little remnant of the CO phase below 150 K. The system exhibits paramagnetism when T 〉 150 K and transforms from paramagnetism to ferromagnetism when T〈 150 K.

关键词： condensed matter physics charge ordering melting solid-state reaction method magnetic properties

高聚物薄膜表面堆起结构的变温原子力显微术研究

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物理学报 2003年第3期52卷 656-663页

作者：王晓平石勤伟中国科学技术大学物理系合肥230026 中国科学技术大学结构分析开放实验室合肥230026

利用原子力显微镜研究了不同温度 (室温至 5 8℃ )及扫描速率 (1— 2 0 μm s)对高聚物PtBuA薄膜 (厚度为133nm)表面上形成的突起结构和周期状堆起结构的影响 .发现较快的扫描速率或较低的温度易产生随机的团状突起 ,较慢的扫描速率或... 详细信息

利用原子力显微镜研究了不同温度 (室温至 5 8℃ )及扫描速率 (1— 2 0 μm s)对高聚物PtBuA薄膜 (厚度为133nm)表面上形成的突起结构和周期状堆起结构的影响 .发现较快的扫描速率或较低的温度易产生随机的团状突起 ,较慢的扫描速率或较高的温度则易形成周期状突起结构 (周期宽度约为 10 0nm) ,且温度和扫描速率对周期状堆起结构的影响定性满足高聚物的时温等效关系 .此外 ,当温度低于高聚物的玻璃化转变温度Tg 时 ,表面粗糙度随扫描次数的增加而增加 ;高于Tg 时 ,表面粗糙度基本不变 .实验表明堆起结构的形成需要高聚物有较大的模量、较小的粘附力和较弱的分子弛豫能力 ,因此该类结构主要在玻璃态才能形成 .

关键词：高聚物薄膜表面堆起结构变温原子力显微术纳米技术

用电泳法制备Zn_xMg_(1-x)O薄膜及其特性研究

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物理学报 2004年第11期53卷 3924-3928页

作者：汪壮兵许小亮陈莹莹周世铭孔宁郭嘉刘洪图施朝淑合肥工业大学物理系合肥230009 中国科学技术大学结构分析开放实验室合肥230026 中国科学技术大学物理系合肥230026

用电泳法制备了一系列ZnxMg1 -xO薄膜 .对ZnxMg1 -xO薄膜的光致发光研究表明 ,在薄膜发射谱的紫外区域有两个显著的峰 ,分别对应自由激子和激子间碰撞的发光 .在可见光区域 ,发射谱的强度基本保持恒定 ,没有发现通常报道的绿光发射 ,说... 详细信息

用电泳法制备了一系列ZnxMg1 -xO薄膜 .对ZnxMg1 -xO薄膜的光致发光研究表明 ,在薄膜发射谱的紫外区域有两个显著的峰 ,分别对应自由激子和激子间碰撞的发光 .在可见光区域 ,发射谱的强度基本保持恒定 ,没有发现通常报道的绿光发射 ,说明生长的薄膜中氧与其他元素保持很好的化学配比 ,抑制了基于氧空位的绿带发射机理 .另一方面 ,薄膜成分中Mg含量的变化和退火温度的变化对薄膜的发射谱有显著的影响 ,表现在ZnxMg1 -xO的紫外发射峰随Mg含量的增加向短波方向移动。

关键词：发射谱薄膜可见光区绿光发射紫外区激子发光发射机短波紫外发射

La_(0.7-x)Dy_xSr_(0.3)MnO_3 (0.00≤x≤0.70)的TCR研究

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中国稀土学报 2004年第6期22卷 760-764页

作者：蔡之让刘宁童伟张裕恒宿州学院材料研究室安徽宿州234000 中国科学技术大学结构分析开放实验室

研究了La位Dy掺杂对La0.7-xDyxSr0.3MnO3(0 00 x 0 70)电阻温度系数(TCR)的影响。实验结果表明:Dy掺杂将引起电阻率曲线的急剧变化,导致出现大的TCR;随Dy掺杂的增加,TCR在x=0.30出现峰值,然后随掺杂量的增加逐步降低。体系出现大的TCR,... 详细信息

研究了La位Dy掺杂对La0.7-xDyxSr0.3MnO3(0 00 x 0 70)电阻温度系数(TCR)的影响。实验结果表明:Dy掺杂将引起电阻率曲线的急剧变化,导致出现大的TCR;随Dy掺杂的增加,TCR在x=0.30出现峰值,然后随掺杂量的增加逐步降低。体系出现大的TCR,来源于Dy掺杂引起的晶格畸变和额外磁性耦合。

关键词：凝聚态物理电阻温度系数额外磁性耦合超大电阻变化稀土

用C-13核磁共振谱测定高聚物中微量异种结构单元的探讨

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分析测试学报 2001年第6期20卷 58-60页

作者：庞文民范成高朱清仁朱原中国科学技术大学结构研究开放实验室安徽合肥230026 中国科学技术大学电子工程与信息科学系安徽合肥230026

通过高低工作频率的高分辩率核磁共振谱仪(型号分别为GX_400和FX_90Q)对含有不同微量异种结构单元的聚乙烯样品作了 13C谱测量和比较分析;结果表明 13C谱在较高磁场频率 (100.4MHz)条件下可检测灵敏度达到0.5个支化点/10000个碳原子(0.5... 详细信息

通过高低工作频率的高分辩率核磁共振谱仪(型号分别为GX_400和FX_90Q)对含有不同微量异种结构单元的聚乙烯样品作了 13C谱测量和比较分析;结果表明 13C谱在较高磁场频率 (100.4MHz)条件下可检测灵敏度达到0.5个支化点/10000个碳原子(0.5/10000C) ;而较低磁场频率 (22.5MHz)只达到1个支化点/1000个碳原子(1/1000C)以上;综合分析所得结果 ,指出在用电磁体系列 (谱仪频率一般为90MHz或100MHz)核磁共振谱仪检测高分子量物质时 ,应注意有遗漏1/1000C以下浓度结构的可能性 ;分析了 13C谱可检测灵敏度与磁场强度等因素的关系 ,得到了可检测灵敏度S/N与磁场强度 (H0)间比较适合的关系式。

关键词：核磁共振高聚物异种结构单元测定碳13 聚乙烯

SOME FRACTAL structureS IN RAPIDLY SOLIDIFIED Al-Mn ALLOY

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Acta Metallurgica Sinica(English Letters) 1992年第3期5卷 203-205页

作者： FAN Chuanguang ZHANG Meng Jiangxi university structure research laboratory,university of science and technology of china,Academia Sinica hefei,chinaWANG Yuansheng WU Ziqin university of science and technology of china,hefei,china Jiangxi Univ China

The fractal structures formed in rapidly quenched Al_(86)Mn_(14)alloy have been observed on *** fractal dimensions are from 1.46 to *** principal phase examined by TEM and X-ray diffractometer is icosahedral quasicrystalline one with a small amount of Al phase. It is believed that these fractal structures are formed by many aggregated particles during the rapid-quenching process.

关键词： Al-Mn alloy rapid solidification fractal structure fractal dimension

REACTION MECHANISM OF BENZOPHENONE-PHOTOINITIATED CROSSLINKING OF POLYETHYLENE

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Chinese Journal of Polymer science 2002年第4期20卷 291-307页

作者： Bao-jun Qu State Key laboratory of Fire science and Department of Polymer science and Engineering university of science and technology of china hefei 230026 china Univ Sci & Technol china State Key Lab Fire Sci Hefei 230026 Peoples R China Univ Sci & Technol china Dept Polymer Sci & Engn Hefei 230026 Peoples R China

The radical intermediates, the crosslink microstructures, and the reaction mechanism of benzophenone (BP)-photoinitiated crosslinking of low-density polyethylene (LDPE) and model compounds (MD) have been reviewed in detail. The spin-trapping electron spin resonance (ESR) spectra obtained from the LDPE/BP systems with spin-trap agents show that two kinds of polymer radical intermediates are mainly formed: tertiary carbon and secondary carbon radicals. The spin-trapping ESR studies of MD/BP systems give further evidence that photocrosslinking reactions of PE predominantly take place a sites of tertiary carbon, secondary carbon, and especially allylic carbon when available. The high resolution C-13-NMR spectra obtained from LDPE and MD systems show that the crosslink microstructures have H- and Y-type links and that their concentrations are of the same order. The fluorescence, ESR, C-13 and H-1-NMR spectra from the PE and MD systems demonstrate that the main photoreduction product of BP (PPB) is benzpinacol formed by the recombination of two diphenylhydroxymethyl (K-.) radical intermediates. Two new PPB products: an isomer of benzpinacol with quinoid structure, 1-phenylhydroxymethylene-4-diphenylhydroxymethyl-2,5-cyclobexadiene and three kinds of alpha-alkyl-benzhydrols have been detected and identified. These results provide new experimental evidence for elucidating the reaction mechanism in the BP-photoinitiated crosslinking of polyethylene.

关键词： photocrosslinking mechanism polymer radical intermediates crosslink microstructures photolytic products of benzophenone polyethylene model compound

Epidemic dynamics on complex networks

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Progress in Natural science:Materials International 2006年第5期16卷 452-457页

作者： ZHOU Tao , FU Zhongqian, and WANG Binghong (Department of Electronic science and technology, university of science and technology of china, hefei 230026, china Department of Modern Physics, university of science and technology of china, hefei 230026, china) [a]Department of Electronic science and technology University of Science and Technology of China Hefei China

Recently, motivated by the pioneer work in revealing the small-world effect and scale-free property of various real-life networks, many scientists devote themselves to studying complex networks. One of the ultimate goals is to understand how the topological structures affect the dynamics upon networks. In this paper, we give a brief review on the studies of epidemic dynamics on complex networks, including the description of classical epidemic models, the epidemic spread on small-world and scale-free networks, and network immunization. Finally, perspectives and some interesting problems are proposed.

关键词： epidemic dynamics complex networks critical value immunization small-world effect scale-free property.