基于极化调控氧空位的BaTiO3/Fe3O4多铁异质结磁电耦合机理研究

Multiferroics with room-temperature magnetoelectric coupling ability has great application potential in future memory with high density and low power consumption. Ionic gating has been employed as a novel method to achieve magnetoelectric coupling, becoming a frontier topic in multiferroic field. Here, it is proposed to deposit BaTiO3/Fe3O4 multiferroic heterostructure and realize room-temperature magnetoelectric coupling via polarization modulated oxygen vacancies. Meanwhile, the in-situ dynamic observation will be carried out to study the physical mechanism of magnetoelectric coupling. The content of this proposal includes as following: Firstly, focusing on the localized regions of interface in BaTiO3/Fe3O4 cross-section sample, atomic force microscopy will be used to in-situ observe the evolution and correlation of polarization-oxygen vacancy-magnetic domain under external electric field. Then, the polarized neutron reflection will be used to quantitatively analyze the correlation of oxygen vacancies and magnetize evolution. Finally, nano-size Fe3O4 array will be deposited on BaTiO3 to realize single magnetic domain state and its magnetoelectric coupling. Based on above mentioned studies, we will clarify the physical mechanism of BaTiO3/Fe3O4 magnetoelectric coupling, providing guidances for magnetoelectric coupling via ionic gating and the development of multiferroic devices.

室温磁电耦合多铁性材料在高密度低功耗存储器领域极具应用潜力，而通过离子调控多铁性材料磁电耦合已成为该领域的前沿与热点。本项目拟制备BaTiO3/Fe3O4多铁异质结，通过铁电极化调控氧空位实现室温磁电耦合，并原位研究其耦合动态演化过程，阐明其微观机理。研究内容包括：（1）运用原子力显微镜原位定性观测外加电场下BaTiO3/Fe3O4截面样品界面处局域的极化-氧空位-磁畴的分布演化和翻转；（2）运用极化中子反射原位定量分析BaTiO3/Fe3O4异质结电致氧空位运动及其磁性关联；（3）以此为基础，制备BaTiO3/Fe3O4纳米阵列，实现Fe3O4单磁畴态及其电控翻转。本项目将深入阐明BaTiO3/Fe3O4磁电耦合的物理机理，为离子调控多铁性材料磁电效应提供新的思路，并为多铁性器件研发提供指导和依据。

项目围绕BaTiO3（BTO）、Fe3O4外延薄膜及其异质结构为主要研究对象，深入研究薄膜厚度、纳米颗粒尺寸及应力应变对极化起源与翻转、铁电场效应、磁畴分布、磁电耦合等现象的调控机制，致力于推动多铁性器件研发与应用。项目研究成果主要包括：（1）通过溶胶-凝胶基的两步溶液处理法制备了(1-x)BiTi(1-y)/2FeyMg(1-y)/2O3–(x)CaTiO3（BTFM-CTO）单晶薄膜，结合极化中子反射原位定量分析明确BTFM-CTO存在室温磁性，通过外磁场实现了BTFM-CTO的极化翻转，证实其存在磁电耦合行为，并对磁电耦合机理进行了分析；进一步引入柔性云母衬底，制备出柔性BTFM-CTO薄膜，观察到力-磁-电耦合现象，实现多场调控铁电极化翻转特性；相关成果发表在National Science Review 2020。（2）通过脉冲激光沉积法制备了无衬底应力束缚的Fe3O4单晶薄膜，证实柔性自支撑Fe3O4薄膜具有优异的弯曲性能，其最小弯曲半径可达7.18 um，同时其磁畴能够通过施加磁场进行可逆地调控，且在摆脱衬底应力束缚后仍然能够维持稳定的磁性能，相关成果发表在Advanced Functional Materials 2020。（3）基于模板法构建了不同尺寸Fe3O4纳米阵列，证实其优异的导电性能；进一步通过自组装法构建了以CoFe2O4（CFO）为纳米点阵的BTO-CFO自组装纳米结构，并发现了室温多铁性，这对于多铁性材料磁电效应的实现提供了新的思路，为多铁性器件研发提供指导和依据；相关成果发表在Nano Energy 2020。项目执行期间在包括Advanced Functional Materials、Nano Energy、Small和Acta Materialia等国际重要学术期刊发表学术论文13篇，申请国家发明专利4项（2项已授权）。