新型多铁材料SrMnO3薄膜的量子调控

During the past decade, multiferroics and related magnetoelectric coupling have attracted intense research interest in both condensed matter physics and materials science due to the wide range of physics insights and associated promising functionalities. Recently, First-principles calculations and experimental results on bulk single crystal have suggested a novel class of multiferroic materials, AMnO3 (A=Ca, Sr, Ba), which have strongly coupled ferroelectric and magnetic orderings due to the spin-phonon interaction. Here we propose a systematic study of the quantum manipulation of the multiferroic orderings in strained SrMnO3 thin films and related functionalities. Using epitaxial strain, we first investigate how the lattice structure can influence the polar instability through spin-phonon coupling, so as to induce ferroelectricity in this magnetic material. Detailed study of ferroelectric properties will be performed to understand the essential mechanism involved. Subsequently, we will study the magnetoelectric coupling in this single phase multiferroic by investigating the influence of magnetic phase transition as well as magnetic field perturbation on the dielectric and ferroelectric properties. We will also explore the possibility to manipulate the magnetic ground state through the epitaxial strain and/or the application of external electric field. Finally, using this novel multiferroic as a model system, we will explore the novel properties and functionalities in the quantum confined and well-designed ferroelectric domain walls. We believe that this project will open a novel pathway to the study of multiferroic and magnetoelectric coupling.

近年来，多铁性材料及其磁电耦合效应因其蕴含的丰富物理和广阔应用前景而吸引了广泛关注。最近，第一原理计算和实验研究揭示了一类全新的单相多铁材料，AMnO3 (A=Ca, Sr, Ba)。因为自旋和声子的相互作用，该材料呈现出与磁序强烈耦合的铁电序。本课题将对应变SrMnO3薄膜中多铁序的量子调控进行系统研究。我们首先通过调节衬底与薄膜之间的应力来了解结构改变与晶格极化畸变的关联以及由此而产生铁电序的物理特性。我们将研究这个体系中的磁电耦合机制；既探索利用磁场控制介电和铁电性质以及利用应力或外加电场控制磁性的可能性。最后基于该模型系统，我们将对铁电畴壁等量子受限系统中的局域导电、磁阻效应等进行研究。我们预期本项研究将为多铁性研究开辟一个全新的道路。

多铁材料及其磁电耦合效应因所蕴含的丰富物理特性和广阔应用前景而吸引了广泛的关注。最近，第一原计算和实验研究揭示了一类全新的单向多铁材料，AMnO3 (A=Ca, Sr, Ba)。因为自旋和声子的相互作用，该材料呈现出与磁序强烈耦合的铁电序。受此启发，本课题围绕应变SrMnO3薄膜的多铁序的量子调控进行系统研究。在本项目的支持下，课题组目前已经完成对于SrMnO3高质量薄膜的制备，有效的解决了国际上众多研究小组所广泛面临的氧缺陷问题的苦扰；在国际上首次实现了对于该样品的本征铁电极化的测量；通过对于该薄膜样品的外延应力依赖研究，发现了应力诱导下的SrMnO3反铁磁基态的演变以及其对于铁电特性的影响。在此基础上，课题组还在本项目的支持下进一步拓展了研究的方向，在铁酸铋中发现了电场诱导的铁电结构相变，不但突出地揭示了多铁性模型体系铁酸铋中尚未发现的巨大的电场可调的弹性特性以及显著的压电特性，为未来的铁电和多铁研究开辟了一个全新的发展空间。同时通过近场扫描微波阻抗谱测量解决了当前铁电畴壁研究中，直流电流小、不易观测等问题，并且这一手段由于微波信号与畴壁的耦合较小，而对畴壁不存在破坏性，能够实现畴壁信号的非破坏性读取。这一研究使铁电畴壁向着新型电子器件应用这一目标又跨出了一步，同时也为其它材料微观导电性研究提供了一种新型的手段。项目执行期间共发表学术论文7篇。在国际会议上作邀请报告9次。