共掺杂BiFeO3薄膜铁电、铁磁性能及磁电耦合的研究

Multiferroic materials have broad applications in sensor, spintronics, information storage and the like. BiFeO3, which simultaneously exhibits ferroelectricity and antiferromagnetic ordering at room temperature, has been widely studied in recent years. One difficult point of current research is how to simultaneously improve the ferroelectricity, ferromagnetism and magnetoelectric coupling in BiFeO3. The subject closely combines with the experimental progress that ferroelectricity can be improved by using A-site and B-site doping (such as A=La, B=Mn) in BiFeO3 and magnetism can be produced by using N doping in SrTiO3 and BaTiO3, grasping the new idea that ferromagnetism and magnetoelectric coupling are improved by using 2p light elements (N, C) doping at O-site in BiFeO3 film, using first-principles to explore the influence of La and N(C) codoping, Mn and N(C) codoping, native defects and doping concentration on the ferroelectricity, ferromagnetism and magnetoelectric coupling in codoping BiFeO3 films. Through analyzing on the geometric configuration, electronic structure and bonding mechanism of the system, getting the microscopic physical model and physical pictures, which can supply theoretical analysis basis and experimental guide for simultaneously improving the ferroelectricity, ferromagnetism and magnetoelectric coupling effect.

室温下同时具有铁电性和反铁磁性的BiFeO3多铁材料在传感器、自旋电子学、信息存储等方面有广阔的应用前景，近来备受人们的关注。如何同时提高BiFeO3材料的铁电、铁磁及磁电耦合性能是当前研究的一个难点。本项目紧密结合BiFeO3中A位掺杂、B位掺杂(如A=La，B=Mn)能大大提高体系的铁电性以及SrTiO3和BaTiO3中N掺杂O位能产生磁性的实验进展，抓住BiFeO3薄膜中利用O位掺杂2p轻元素(N、C)来提高体系铁磁及磁电耦合的新思路，用第一性原理计算方法探索La和N(C)共掺杂、Mn和 N(C)共掺杂、及本征缺陷和掺杂浓度对BiFeO3薄膜铁电、铁磁及磁电耦合性能的影响。通过对体系的几何构型，电子结构及成键机制的分析，获得微观物理模型和物理图像，为同时提高BiFeO3材料的铁电、铁磁及磁电耦合性能提供理论分析基础和实验指导。

如何提高BiFeO3 (BFO)材料的多铁性能是当前学术界研究的一个难点。本课题主要从La、Mn、N等元素掺杂方面对BFO的多铁性能进行了系统的研究。在三年的资助期间，本项目主要完成了以下重要成果：(1) 我们对非磁性N元素掺杂R3c空间结构的BFO体系的磁性能进行了系统的研究，发现N掺杂促使体系显示出铁磁性，进一步研究发现Bi本征缺陷增强了掺杂体系的磁性能而O缺陷大大减弱了体系的磁性能；(2) 我们对P4mm 结构的BFO掺杂La、Mn、N元素的磁性能进行了系统的研究，发现Mn和N掺杂BFO体系均表现出铁磁性，而La掺杂体系无磁性。Mn和N共掺杂BFO表现出更为稳定的铁磁性，而La和N共掺杂和单独的N掺杂BFO结果基本一致。(3) 我们深入研究了La、Mn、N元素掺杂P4mm 结构的BFO的自发极化变化，发现自发极化值由原来未掺杂的149.2 µC/cm2分别改变为154.4µC/cm2，145 µC/cm2和147.3 µC/cm2。Mn、N共掺杂及La、N共掺杂BFO的极化值分别为136.9 µC/cm2和177.88 µC/cm2。本课题的研究结果揭示了不同元素掺杂影响BFO体系多铁性能的微观物理机制，对BFO材料在掺杂改性方面具有一定的指导意义。