论文标题:双掺杂CMR薄膜的结构和光电特性研究
Investigations of Light-induced Photorefractive Spatial Channel Waveguides
论文作者 汪世林
论文导师 宋宙模,论文学位 硕士,论文专业 光学工程
论文单位 西北工业大学,点击次数 95,论文页数 79页File Size3861k
2003-03-01论文网 http://www.lw23.com/lunwen_61180142/ 特大磁电阻效应;钙钛矿结构;双交换作用;杨-特勒效应;薄膜光响应;电子自旋;负阻效应;磁控溅射;液氮低温
CMR,Perovskite structure,Double exchange,Photoinduced effect,Electronic spin,Magnetron sputtering,Liquid nitrogen low temperature
依次用固相反应法和射频磁控溅射法成功制备了双掺杂钙钛矿CMR锰氧化物La_(2／3)(Ca_(1-x)Sr_x)_(1／3)MnO_3系列(x=0，1／3，2／3和1)块状晶体和薄膜。XRD测试表明两种方法制备的材料均为钙钛矿结构。 对薄膜的XRD分析、伏安特性、电阻率-温度特性、磁电阻效应以及光致电阻率变化效应显示，Ca、Sr双掺杂可实现对钙钛矿锰氧化物特性的可操作性控制，为此类材料在室温范围的应用提供重要的参考思路。所制备的样品中，La_(2／3)Ca_(1／3)MnO_3薄膜连续激光光诱导信号极大值(ΔR／R_(opt))_(max)达到43.5％，据我们所知，已经属于国内外先进水平。调制激光脉冲实验表明，光致电阻变化率ΔR／R_(opt)的强度和温度及偏置电流之间表现为强烈非线性关系：(ΔR／R_(opt))_(max)为偏置电流的二次函数，而极大值对应的温度和偏置电流成线性关系，同时，光响应有一个截止温度，对于La_(2／3)Ca_(1／3)MnO_3薄膜，存在最佳光响应条件(偏置电流I=24.7mA和温度T=229K)。 根据薄膜的伏安特性负阻现象，磁场、光场、温度场的响应特性的实验结果比较发现，CMR薄膜材料在电场、温度、磁场和光场几种外场作用时的特性变化可能存在共同的内部机制：都是由于Mn离子3d轨道e_g↓巡游电子状态受到外场调制作用所引起。
Perovskite crystals and thin films of La2/3(Ca1-xSrx)1/3MnO3 with x ranging from 0 to 1 have been prepared with solid state reaction and RF magnetron sputtering method, investigated by various techniques:XRD analysis, resistivity in low temperature scope, magnetoresistance, cw laser and modulated laser pulse induced resistivity changing, etc.Experiments phenomena show that the properties of these materials are related with the Ca and Sr double doping level greatly, especially in photoelectrical characteristics. All samples exhibit phase transition (FM-PM) when temperature of them is increased. It is showed that the maximum of photoinduced resistivity changing ratio (ΔR/Ropt)max and its appearing temperature respectively decreases and increases when the doping level x changes from 0 to 2/3. (Δ R/Ropt)max reaches 43.5% when x is 1 ,which is an exciting figure in this research field. Experiment results show that ( ΔR/Ropt)max is strongly dependent on bias current and temperature, and the relationship among them shows a nonlinear behavior. What is more,there exists an optimal bias current and temperature condition for optical response in La2/3Ca1/3MnO3 thin film.The results of our experiments suggest that there maybe exist a common mechanism in resistivity-temperature property, CMR effect and photoinduced effect: the state of down spin eg carriers in spin order system.
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