钙钛矿锰氧化物/铁电体二维异质结构在应力作用下的界面耦合及光响应特性

Enhancing magnetoelectric coupling always is hot issue for multiferroic research, and response to external field of multiferroics is also of great concern. In this project, the ferroelectric control of spin ordering at interface will be explored by structuring ultrathin magnetoelectric heterostructure (e.g. short-period superlattices) to generate the reconsitution of interface electronic states in perovskite manganites, using the first principles based on density function theory as well as nonequilibrium green's function. Then, we will further investigate magnetoelectric effects as lattice strain (i.e., epitaxial strain) changes for these two-dimension multiferroic systems, especially ferroelectric modulation of spin ordering, orbital magnetization and spin-polarized carrier mobility at interface. These studies are helpful to develop the ferroelectric and strain control-mechanisms of interface magnetization in perovskite manganites. The effects of epitaxial strain and electric polarization on the optical response will be studied systematically, exploring the technological approaches for modulating optical response via lattice stress and interface coupling in the two-dimension multiferroic systems with strong magnetoelectric coupling. This research not only will be of scientific significance for the active controls of low-dimension interface electron states and physical properties of strongly-correlated electron systems, but also can provide theoretical guidance for development of the multifunctional field control and spintronics devices in magnetoelectric materials.

有效强化多铁材料铁电序-磁序参量耦合一直是多铁性研究的热点问题，多铁材料外场响应的研究也备受关注。本项目拟采用基于密度泛函理论的第一性原理和非平衡格林函数方法探索通过构造钙钛矿锰氧化物基磁电异质结构（如超晶格），产生多铁界面电子态重构，以实现局域自旋序的铁电控制。进一步研究此异质界面二维体系在晶格应力（即外延应力）畸变下的磁电耦合效应—包括铁电极化对界面自旋序、轨道磁矩、自旋极化载流子迁移特性等方面的影响，阐明钙钛矿锰氧化物界面磁化的铁电、应力双调控原理和方法；研究外延应力和铁电极化对此二维多铁系统光响应特性的影响规律，揭示其微观机制，探索通过晶格应力、界面耦合对二维多铁系统光响应进行调制的技术途径。研究结果不仅对深刻认识电子强关联体系低维界面电子态和物理性质的主动控制具有科学意义，而且能够为此类磁电材料的多功能外场调控及自旋电子器件的研制提供理论指导。

强化磁性材料电荷—自旋参量耦合多年来一直备受关注，如何方便、高效地实现磁性的外场调控仍然是材料工程领域的研究热点。使用基于密度泛函理论的第一性原理方法，本项目中我们研究了短周期SrMnO3/BaTiO3/LaMnO3 (001)三色超晶格、超薄La2/3Sr1/3MnO3/SrTiO3 (001)异质结等体系的磁电耦合性质。获得的主要结果如下：（i）自旋轨道耦合计算模式下，(SrMnO3)2/BaTiO3/(LaMnO3)2 (001)超晶格铁电极化翻转诱导了体系的磁性重构，界面Mn原子实现了自旋翻转，超薄LaMnO3层由反铁磁基态转变为铁磁基态。磁各向异能（MAE）计算结果显示电极化翻转对MAE的影响较弱，轨道磁矩亦如此。光学计算结果显示，铁电极化对三色超晶格光吸收特性具有潜在的调控效应。随着铁电极化从P(z)态翻转为P(-z)态，体系在近红外区的吸收得到明显改善，红外区响应更加局域化。（ii）对于La2/3Sr1/3MnO3（记为LSMO）层厚度n＜10 u.c.的超薄(La2/3Sr1/3MnO3)n/SrTiO3 (001)异质结，依赖于膜厚和界面原子层堆垛结构，二维体系表现为顺磁性或反铁磁性，与近期实验结果符合。探究电场对异质结磁性的影响，发现在较小外场作用下不易调控(La2/3Sr1/3MnO3)3/SrTiO3 (001)异质结和(La2/3Sr1/3MnO3)4/SrTiO3 (001)异质结的自旋序。而对于n=5 u.c.的超薄异质结而言，当沿[001]正方向的电场强度大于0.4 V/Å时，体系可能从顺磁（或反铁磁）转变为铁磁，因此展现了强烈的电磁耦合。部分相关工作（n≥6 u.c）有待于进一步开展。所得结果有望为发展新一代多态信息存读、多功能自旋电子学材料和器件探索新的技术途径，具有一定的科学意义。