六方锰氧化物薄膜多铁性能的第一原理设计与研究

Multiferroic materials have a great and potential research value for applications in multiple-state memory elements, electric-field-controlled ferromagnetic resonance devices, spintronics, etc. Recently, multiferroic manganite is one of the most important families in multiferroic materials who has excellent properties, richness and complexity of physical phenomena. In the project, we will choose the hexagonal RMnO3(R=Y, Ho, Lu, etc) thin films as the object of study because they have potential applications and good prospects in the field of multiferroics materials. On consideration of heteroepitaxial constraints (such important variables as strain, interface termination, etc.), we will investigate the multiferroic properties of manganite films with various substrates by means of first principles methods based on density functional theory, combined with high resolution transmission electron microscopy and molecular dynamics simulation. To study the effect of microstructure defects on the multiferroic properties of manganite films, we will lay emphasis on finding the dominant factors to significantly increase the antiferromagnetic Néel temperature. To reveal the microscopic mechanisms responsible for coupling between ferroelectric and ferromagnetic order parameters of hexagonal manganites, we attempt to work out a close association between density functional theoretical design and experimental film control. After implementing the project, we will not only have gained an insight into the coupled behaviors and interactions between the charge, spin, orbital, and lattice degrees of freedom of multiferroic films, we will also have provided the theoretical references for evaluation of great potential applications of hexagonal manganite thin films in the field of new-type functional materials and device designs.

多铁性材料在多态存储器元件、电场控制铁磁谐振装置、自旋电子学等方面有着巨大潜在的研究价值。近年来，多铁性锰氧化物因其优异的性质、丰富的物理现象成为多铁材料家族中的核心力量。 本项目拟以在多铁性材料领域中有着重要潜在应用价值的六方RMnO3(R = Y、Ho、Lu等)薄膜为研究对象，采用基于密度泛函理论第一原理方法为主要手段、并与高分辨透射电子显微术和分子动力学计算相结合，考虑异质外延约束限制(如应变、界面终止面等重要变量)，通过研究不同类型衬底薄膜多铁性性质，探讨微观结构缺陷对薄膜多铁性能影响，重点寻找能够显著提高薄膜反铁磁奈尔温度主导因素，建立理论设计和实验薄膜控制之间密切联系，揭示六方锰氧化物铁电性和铁磁性互相耦合微观机制。项目的完成不仅有助于探索多铁性薄膜电荷、自旋、轨道和晶格自由度之间耦合和相互作用，而且也为六方锰氧化物薄膜在新型功能材料与器件设计领域中应用潜力的评估提供理论参考。

项目运行期间，我们利用第一原理计算对多铁材料六方锰氧化物中的代表YMnO3的原子结构、铁电性、磁性以及磁电耦合进行了研究，发现Gamma3型反铁磁结构具有与实验相符的能隙,各种磁结构的铁电极化并不相同，这意味着YMnO3具有较强的磁电耦合作用，可以通过调控磁结构来改变材料的铁电性能。通过第一原理计算不同应变条件下以及La原子掺杂的YMnO3的磁交换作用，我们发现张应变可以提高YMnO3的奈尔温度，La原子掺杂则会更进一步的提高温度，这些发现对于研究六方锰氧化物的磁性相变、开发室温多铁材料等方向具有积极的指导意义。在实验方面，我们成功的在不同衬底上生长了YMnO3薄膜，利用透射电镜对界面结构进行观察，这对于薄膜材料的制备提供了有益的指导。此外，我们还对异质多铁材料Fe/BaTiO3界面上的空位进行了研究，发现当复合薄膜体系的界面存在一定量的空位时，不仅可以增加界面结构的成键强度，更为重要的是没有改变该体系的磁电耦合性质。项目执行期间在Journal of Applied Physics、Computational Materials Science等国际知名学术期刊上发表多篇学术论文。