基于渗流效应的高磁电耦合铁电/铁磁多铁复相薄膜形成及其机理研究

In general, for high efficient magnetoelectric coupling in the ferromagnetic/ferroelectric composite thin film, the special microstructure, such as 1-3 structure which has 1-dimentianal parallel ferromagnetic phase wires assigned in ferroelectric matrix phase along the normal direction of the thin film, must be designed for generating anisotropy distortion of the ferromagnetic phase while stressed by the homogeneous dispersed ferroelectric matrix. The issue of difficult realization of magnetoelectric coupling in traditional composite systems, limit the practical and high quality application of multi-ferroic composite thin films. This project proposed to solve the problems by systematically studying the fundamental issues of multiferroic and the magnetoelectric coupling. In order to achieve highly efficient magnetoelectric coupling in the composite thin film prepared by conventional deposition methods, the anisotropy percolation threshold in different orientations of thin film is introduced to form strings of stacked ferromagnetic nano crystalline phase particles and the single-crystal substrate is adopted to control the growth of magnetic phase in special orientation in the composite thin film. The 1-3 like topological structure can be well controlled to realize with conventional technologies, such as RF sputtering which are widely used for preparation of traditional composite thin film, in which the two step processes of forming amorphous phase initially and then crystalline phase based on nucleation/crystallization mechanism. In this case, the problem that magnetoelectric coupling is hard to realize in the traditionally prepared composite thin film can be solved successfully by generating the anisotropy distortion of the ferromagnetic phase while stressed by the homogeneous dispersed ferroelectric matrix. Hence, high magnetoelectric coupling will be obtained in the multiferroic composite thin film prepared by conventional method. It is obvious that this project will promote the development of the multiferroic composite thin films and be beneficial to new applications of multifunctional electronic devices. Beside, very promising preliminary result which is almost the same as the best one reported by using the special designed 1-3 structure has been obtained to prove the idea concerned.

项目针对复相多铁薄膜,考虑铁相间高效磁电耦合通常仅在经特殊的复杂结构设计后能通过两相间产生各向异性应力传递的体系中产生，而不易在传统方法制备的复合体系中获得等难题,提出了在复相薄膜中通过引入渗流效应，利用简单的传统原位沉积工艺制备高耦合特性多铁复合薄膜的新观点。项目以这种新型复合薄膜为目标,基于复相中渗流效应产生以及渗流阈值的方位各向异性控制特点, 利用如磁控溅射等传统薄膜生长技术, 经先控制形成非晶再成核/析晶的两步法过程并利用基板诱导铁磁相取向生长，实现在原位随机生长的两相复合薄膜中形成取向铁磁相纳米串，且原位形成的纳米串沿薄膜法向排列并镶嵌于铁电相基体中，最终形成在两相间具有各向异性应力传递特点的类1-3结构复合多铁薄膜, 以解决目前无法在传统两相复合多铁体系中产生高磁电耦合的难题。初步结果已经获得了与目前报道的最佳性能相当的高磁电耦合性能，研究对复相多铁薄膜的发展和应用具重要意义。

由一维取向的铁磁相埋入三维铁电相本体中制成的1-3微结构复相多铁薄膜，受到各向异性作用力而产生良好的磁信号响应。然而，如何解决在薄膜中不通过人工植入单晶的或取向的一维阵列等复杂工艺而直接利用简单的原位制备技术制备薄膜是真正能拓展其在新型多功能器件中广泛应用的关键。.本项目分别利用NZFO 和BTO作为铁磁相和铁电相原料在半导体行业最常用的单晶硅基板上制备铁电铁磁复相薄膜材料。.项目成功通过溶胶凝胶法并利用相分离技术，原位生长了均匀分散于薄膜中且被成功控制沿（111）取向生长的单晶微柱状NZFO阵列，得到了（111）取向生长的NZFO相微柱阵列复相薄膜。利用薄膜中NZFO和BTO分别掺杂有Ti和Fe离子的特征，调制使晶相形成过程中与基板的接触角及异相成核势垒变小，并同时将首层膜厚度控制得极薄，使NZFO易沿平面扩展生长的同时，再结合利用立方相的NZFO本身（111）晶面具有相对低表面能的特性，控制NZFO在极薄膜层中以（111）晶面取向生长，从而获得NZFO相为（111）取向生长的首层薄膜。最后经逐层诱导在硅基板上获得原位生长（111）取向NZFO相微柱阵列复相薄膜。在其铁电相BTO居里温度的~398K附近，薄膜的磁化强度变化达到～40%。.项目还基于渗流理论，成功利用在不同维度系统中渗流阈值不同的效应，通过磁控溅射方法，利用传统制备0-3形复合薄膜的方法成功在硅基板上原位制备了类1-3型NZFO-BTO复相薄膜。其中NZFO相被巧妙控制形成了纳米晶粒相互接触且沿法向排列的一维纳米晶串，获得了类1-3结构NZFO-BTO复相薄膜。同时，利用硅基板晶格的外延控制，实现了（100）取向生长。薄膜同样表现出了很强的ME耦合特性，在约400K时，其磁场强度变化依然达10%以上。尽管可能由于其实际为类一维磁相，且为不同于NZFO易磁化轴（111）方向的（100）取向，而未表现出最强的磁化强度变化。.综上，这类NZFO/BTO复相薄膜表现出了很大的ME耦合特性，甚至比已有报道的硅基板上薄膜的性能要高得多，有望在以硅基板为主的半导体行业内作为高效ME耦合多铁薄膜材料在新一代功能器件中得到广泛应用。

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