掺杂对双钙钛矿多层薄膜的结构和电磁性能的影响及第一性原理研究

For a series multilayer films of the ordered and doped half-metallic double-perovskite A2BB'O6（A=Sr, Ba；B=Mn, Fe, Co；B'=Mo, Re）, we will inspect the effect of the microstructures (including modulate periods, grain sizes and their distributions, defect types and densities, etc.) on the mechanisms and rules of the electronic and magnetic properties of the double-perovskite multilayer films; The optimized structural parameters and fabrication technologies will be determined for obtaining the high-quality double-perovskite multilayer films with high Curie temperature (Tc), high magnetoresistance (MR), low saturation magnetic field (Hs) and low resistance-temperature dependent characters; The electronical structures of the corresponding double-perovskite multilayer films will be calculated by using the first-principles and compared with the measured results of the x-ray absorption spectroscopy (XAS), ultra-violet photoelectron spectroscopy (UPS) and electron energy loss spectroscopy (EELS); The experimetal results will be explained by using the Hund’s rules, Pauli exclusion principle, crystal field theory, Jahn-Teller effect, double-exchange and superexchange mechanisms together with first-principles calculations as well as the scattering of the spin electrons inside of the grains (including ponit defects and dislocations) and the insulating layers as well as on the grain boundaries, film-substrate and film-insulating interfaces; The theoretical fundations of the electromagnetism will be set up for double-perovskite multilayer films and used as a theoretical supporting and technical guidance for theory developments and device applications, respectively.

针对有序和掺杂半金属双钙钛矿A2BB'O6（A=Sr、Ba；B=Mn、Fe、Co；B'=Mo、Re）系列多层薄膜，考察调制周期、晶粒尺寸及分布、缺陷类型和密度等微观结构对双钙钛矿多层薄膜的电磁性能的影响机理及规律；确定制备高居里温度Tc、高磁电阻MR、低饱和磁场强度Hs和低电阻-温度依赖的双钙钛矿多层薄膜的最佳结构参数及制膜工艺；采用第一性原理计算相应结构双钙钛矿多层膜的电子结构并与对应样品的XAS、UPS和EELS的测量结果比较；同时考虑自旋电子在晶粒内部（包括点缺陷和位错）以及晶界、膜-基界面、膜-分隔层界面、分隔层等中的散射作用，根据洪德定则、泡利不相容原理、晶体场理论、Jahn-Teller效应、双交换和超交换机理并结合第一性原理计算对实验结果进行分析；建立双钙钛矿薄膜材料的电磁学理论基础，为自旋电子学的理论发展及器件应用提供理论支持和技术指导.

双钙钛矿（A2BB'O6）因其半金属铁磁性及其高居里温度Tc广泛用于磁阻和自旋电子学器件中。考虑到实际材料中不可避免的存在缺陷以及以薄膜形式应用的实际情况，本项目针对Sr2FeMoO6，Sr2FeReO6，Pb2FeMoO6，Pb2FeReO6等双钙钛矿材料，研究了各种缺陷和各种截止薄膜对这些双钙钛矿材料的结构，电子和磁性的影响机理和规律。如对双钙钛矿Pb2FeMoO6（001）取向薄膜的3个可能截止的研究发现：近表面几层向外弛豫，PbO层的弛豫分数皱褶s比相邻FeMoO4层的大，且二者均有从表面层到内部层的减小趋势。无论是平行于或垂直于表面，Mo-O键长总是短于相邻的Fe-O键长。半金属铁磁（HM-FM）特性确保了双钙钛矿Pb2FeMoO6（001）取向的3个可能截止薄膜在磁阻和自旋电子学器件中的潜在应用。FeMoO4第一层上的Fe原子周围自旋电荷密度的非局域分布导致FeMoO4第一层上的Fe原子的磁矩比内部Fe原子的小。根据洪德定则、泡利不相容原理、晶体场理论、Jahn-Teller效应、双交换和超交换机理并结合第一性原理计算建立了双钙钛矿薄膜材料的电磁学理论基础，其结果对于自旋电子学的理论发展及器件应用具有一定理论意义和实用价值。