多铁纳米岛的畴结构及磁电耦合调控

Multiferroics have potential applications in high speed, low power consumption, and ultrahigh density data storage and data processing. One the other hand, the size effects in low dimensional nanoscale multiferroics can greatly affect their domain structures and magnetoelectric properties, which can be considered as a powerful tool to tailor their physical properties. However, the investigations on nanoscale multiferroics are still in a preliminary stage. In this work, we proposed the study of domain structures and magnetoelectric properties in epitaxial multiferroic nanostructured islands. The objectives are: (1) to fabricate well-expiaxial, size and shape controllable, high quality BiFeO3, as well as BiFeO3/CoFe2O4 and BiFeO3/Co multiferroic nano-island array; (2) to study the effects of size and substrate strain on the nano-domain structures and related mechanisms in single phase multiferroic nanoislands, and to obtain stable and controllable domain structures (especially topological domains); (3) to study the size effects on magnetoelectric properties and related mechanisms in mulitferroic heterostructured nanoislands, and to achieve a controllable electric induce magnetization reversal of nanomagnets; (3) to explore their domain related novel physical properties, such as conductivity and optical properties. These studies may deepen our understandings on size effects on domain structures and magnetoelectric couplings and related mechanisms, and brings us high quality multiferroic nanoislands with superior properties, which may promise for high density recording devices.

多铁性材料有望用于高速、低能耗、高稳定性、超高密度的新型存储及逻辑器件。低维纳米点尺寸效应可显著影响多铁性电畴结构和磁电耦合特性，成为性能调控的有力手段。但相关研究还处在初期阶段，有待深入。本项目力图在前期工作基础上，开展单一多铁纳米岛内畴结构和磁电耦合调控研究，在此基础上推广到高密度纳米岛阵列上。主要目标为：(1) 制备高品质外延且形状和尺寸可控制的BiFeO3纳米岛、BiFeO3/CoFe2O4及BiFeO3/Co纳米岛阵列；(2) 研究尺寸效应和衬底应变对纳米岛内畴结构的调控，厘清调控机制，获得稳定可控的畴结构(尤其是拓扑畴结构)；(3) 研究复合多铁异质结纳米岛内磁电耦合的调控和增强机制，实现纳米磁畴可控反转；(4) 探索畴结构相关新颖物性，如光学、电导特性等。本项目有望深入了解纳米尺度下多铁畴结构、磁电耦合调控机制及相关新颖物性，获得高性能材料，为高密度存储器件应用打下基础。

多铁性材料有望用于高速、低能耗、高稳定性、超高密度的新型存储及逻辑器件，从而成为当前前沿热点。由于低维纳米点尺寸效应可显著影响多铁性电畴结构和磁电耦合特性，成为性能调控的有力手段。本项目的研究工作严格按照基金委审核通过的任务书进行研究，在四年的研究过程中取得了一系列成果，超额完成全部研究任务。主要成果包括：1）制备了高品质外延且形状和尺寸可控制的BiFeO3纳米岛、BiFeO3/ CoFe2O4 及BiFeO3/Co纳米岛阵阵列；2）获得了稳定可控的畴结构，包括中心型和涡旋型拓扑畴，并实现往复翻转与擦写；3）在多铁异质结中实现了可控的电控三角形磁畴120o畴反转，以及电场调控斯格明子等实现非失性、稳定的的多拓扑态翻转；4）揭示了中心型拓扑畴形成的电荷缺陷的影响机制、电控磁翻转的调控应变机制，并提出构筑铁电拓扑畴器件原型。成果为开发基于铁电和多铁材料的新型高密度及低能耗的存储与逻辑器件提供了理论和技术基础。.共发表SCI论文28篇，包括1篇Nature Communications，1篇Science Advances，1篇Advances Materials，1篇Advanced Functional Materials 封面论文，1篇National Science Review，4篇ACS Appl. Mater. Interfaces，1篇ACS Nano等，其中影响因子>10的论文6篇；申请与授权发明专利12件；组织举办了国际会议1次（2019AFM2，项目负责人任大会共同主席）；培养毕业博士研究生4名，毕业硕士研究生12名，博士后1名；引进青年骨干人才3名，培养青年珠江学者1名，广州市珠江新星1名，项目负责人先后获省级和国家级人才计划的支持，并获2020 国际先进材料协会（IAAM Scientist Award）奖。