自旋失措结构CuFeO2基材料微结构对多铁性能影响机理的正电子实验研究

Multiferroic material CuFeO2 (CFO) with spin frustration structure exhibits extraordinary magnetic structure and strong magnetoelectric coupling effects. It has attracted considerable attention due to its rich physical implications and potential application prospect. However, the ferroelectric property of this material is weak and its electromagnetic tuning mechanism remains unclear. Based on the strong electron correlation between the electrical/magnetic properties and electron structure, defects characteristics in CFO system, this project is meant to adopt the positron annihilation and other techniques to probe into the following issues: ① To study the relevance of the microstructure and the ferroic orders near the antiferromagnetic transitions temperature region, and to clarify the spin-lattice coupling mechanism of CFO system; ② To explore the effect of doping ions and occupied position on the crystal structure, magnetic structure, electron structure, defect characteristic and the electron-phonon coupling of CFO system, to reveal the mechanism of ferroelectric polarization and magnetoelectric coupling behavior induced by the substituting ions; ③ To study the effects of the parameter of laser beam irradiation on the electron structure, defect evolution, electric/magnetic domain, spin and polarization order of CFO films, to obtain the key factors to modulate the electrical/magnetic properties. Combined with the theoretical calculation, the mechanisms of microstructure on the electrical/magnetic properties of CFO system will be illuminated. This study can provide the basic experimental data for the explanation of multiferroic machnism and application of multiferroic material with spin frustration structure, meanwhile it can provide the experimental evidence for the application of positron annihilation technology on researching in these kind of materials.

自旋失挫结构的多铁材料CuFeO2 (CFO)独特的磁结构和强磁电耦合效应展示出丰富的物理内涵和潜在的应用前景。然而，其铁电性弱，且电磁调控物理机制尚不明朗。基于强关联电子体系CFO电磁性能与电子结构、缺陷特征密切相关，本项目拟采用正电子湮没等技术，①研究 CFO在反铁磁相变温区微结构与其铁性参数之关联规律，阐明体系自旋-晶格耦合机制；②探究掺杂离子特性和占位对体系晶体结构、磁结构、电子结构、缺陷特征及电-声耦合作用的影响，揭示离子掺杂对体系铁电极化的诱导机理和磁电耦合机理；③研究脉冲激光束辐照参数对CFO薄膜体系电子结构、缺陷演化、电/磁畴、自旋和极化序等微观参量的影响，得到调控体系电磁性能的关键因素。结合相关理论计算，阐明CFO材料微结构对体系电磁性能的影响规律及调控机制。本项目将为阐明具有失挫结构材料多铁机理研究及应用提供基础实验资料，为正电子技术对该类材料的研究提供实验例证。

多铁材料CuFeO2(CFO)独特的磁结构和强磁电耦合效应展示出丰富的物理内涵和潜在的应用前景。然而，其电磁调控物理机制尚不明朗。本项目将CFO作为研究对象，合成了多个系列的CFO陶瓷/薄膜实验样品，利用正电子湮没技术、X射线衍射、拉曼光谱等测试手段对各系列的CFO材料进行微结构表征，以研究体系微结构对体系多铁性能的调控和影响机理。在此基础上，拓展研究了CFO体系巨介电性能和光学性能机理。主要研究内容：①制备工艺对CFO体系微结构和磁/电性能的影响研究，发现在预烧温度为850-870℃、成型压力为100MPa、烧结温度/时间为1000℃/30h的制备条件下，易于形成单相CFO陶瓷。实验样品展示出良好的磁性能和巨介电性能(相对介电常数εr>10000)。②温度对CFO体系电子结构和缺陷演化以及磁/电性能的影响研究，发现在100K附近，体系从顺磁相转变到自旋液相与体系局域电子密度的突变有关。③离子掺杂对CFO体系微结构和磁/电/光性能的影响研究，制备了Fe位稀土离子和过渡金属离子、Cu位碱金属离子和碱土离子掺杂的多个系列实验样品，厘清了掺杂离子占位、尺寸、价态、浓度等因素对体系微结构、磁、电、光性能的影响规律。④制备条件和脉冲激光束辐照对CFO薄膜微结构和分子极化的影响研究，发现薄膜样品沉积时间在120-180min、800℃温度退火制备的CFO薄膜样品相结构单一，光学性能稳定；发现激光辐照改变了CFO的化学成分，产生了Fe2O3和CuO杂质；辐照改变了CFO薄膜的应力状态，增强了CFO体系Fe-O键和Cu-O键的分子极化程度。本项目研究结果为揭示CFO晶格畸变、微观形貌、缺陷特征、电子结构等微结构对体系磁/电/光性能的影响机理提供重要的实验数据；为正电子湮没技术对该体系物性的研究提供了实验支持，同时为正电子理论的完善提供基础研究资料。