BTO-(111)NZFO复相多铁薄膜结构及磁电耦合性能的调控机制研究

Multiferroics composite has attracted great attention because of the excellent properties and great application potential. At present, the BTO-(100)NZFO composite thin film with 1-3 like structure prepared by simple 0-3 process exhibit a strong magnetoelectric coupling, due to the anisotropy of percolation threshold in low dimension materials and strain transmission in 1-3 structure. Although this composite thin film promotes the development of multiferroics, the lattice strain cannot be utilized mostly by the (100) orientated NZFO. To address this issue, the BTO-(111)NZFO composite thin film prepared by 0-3 process on induced layer is proposed. The magnetoelectric coupling is improved by controlling the angle between magnetic dipoles and external field, promoting the rotation rate of dipoles in distorted NZFO lattice, when the high anisotropic contact and strain transfer between constituent phases is retained. For now, it has been preliminarily proved that the (111) oriented NZFO in composite thin film can form due to the induced effect (001)Al2O3/(111)Pt. Later on, the systematic study will be performed on the growth mechanism of BTO-(111)NZFO composite thin film and the control of magnetoelectric coupling by NZFO’s orientation. By revealing effect of NZFO’s orientation on the contact between constituent phases and establishing the model describing the rotation of dipoles in distorted lattice, the structure and magnetoelectric coupling of multiferroic composite thin film is controlled effectively and the magnetoelectric coupling strength is improved efficiently.

复相多铁材料因优异的性能和巨大的应用前景而广受关注。目前，利用渗流通道在低维材料中形成及晶格应变在1-3结构中传递的各向异性，0-3工艺成型的类1-3型BTO-(100)NZFO薄膜初步实现了高磁电耦合性能和简单制备工艺的统一。但NZFO的(100)取向并不能最大限度地将晶格的各向异性应变转化为磁电耦合性能。针对此问题，本项目提出通过0-3工艺和晶格匹配诱导作用制备BTO-(111)NZFO薄膜，在维持两相间高各向异性接触和应变传递的基础上，调整偶极子与外场间的夹角，加快偶极子在形变晶格中的转动速率，提升材料磁电耦合性能。在初步证实(111)NZFO可通过(001)Al2O3/(111)Pt诱导形成的基础上，深入研究BTO-(111)NZFO薄膜的结构和磁电耦合效应的取向调控机制，掌握NZFO取向对两相接触方式的影响规律，建立偶极子在形变晶格中的转动模型，实现材料磁电耦合性能的巨大提升。

1-3型复相多铁性材料具有尺寸小以及强磁电耦合性能的优势。为以简易方式制备出具有高磁电耦合效应的1-3型复相多铁材料，本研究开展了以BaTiO3(BTO)-Ni0.5Zn0.5Fe2O4(NZFO)复相薄膜为对象的研究，取得了以下主要结论：.1、通过溶胶凝胶法循环旋涂循环热处理法可成功在单晶硅(111)基板上制备NZFO(111)取向生长的BTO-NZFO复相薄膜。改变热处理温度及复相薄膜的配比，可使组成相晶粒尺寸、杂质相以及取向度可控。NZFO晶粒尺寸最大可调控为600 nm；当热处理温度升高至1100℃时，杂质相Ba2TiSi2O8(BTSO)消失；当热处理温度为1050℃，0.9NZFO-0.1BTO薄膜中NZFO取向度高达799.6。.2、BTO-NZFO复相薄膜的取向生长与单晶硅衬底的外延诱导无关。NZFO相沿(111)晶面取向生长是Ti4+离子掺杂诱导调控的。通过调控NZFO相的Ti4+离子掺杂浓度以及复相薄膜的组成相配比可改变薄膜与基板之间的界面能和接触角、改变薄膜异相成核势垒，使其保持最低值，从而使薄膜中NZFO相的结晶成核能力最佳。在异相成核模式下，NZFO原子迁移至最低能量面而实现(111)取向生长。当热处理温度为1100℃，复相薄膜中NZFO相含量为0.9时，薄膜的接触角为最小值~10或低于此值，NZFO的取向度为300.97。.3、基于分相控制复相薄膜中(111)取向的NZFO晶相以一维柱状微结构排布。高温热处理的BTO-NZFO复相薄膜因体系中能量的涨落起伏导致旋解分解，诱发 BTO和NZFO发生分相行为。毗邻单晶硅基板的第一层薄膜为晶种分相层，可为后续逐层复相薄膜起到诱导取向作用，使得逐层复相薄膜中的NZFO晶粒在沿(111)晶面生长。.4、BTO 纳米晶二次填充法可成功制备1-3型BTO-NZFO复相薄膜。BTO纳米晶有效填入到NZFO柱状阵列的间隙中，使NZFO柱状结构被纳米级BTO相间隔和包覆，最终实现了在单晶硅基板原位制备出一维NZFO晶相埋入三维BTO 基体相的1-3结构薄膜。此结构复相薄膜的磁电耦合效应高达44.8%。当BTO在居里温度点经历铁电-顺电相变时，BTO的晶格应变通过应力的形式传递给与之接触的NZFO相，(111)取向生长的NZFO晶格受到各向异性应力后的晶格形变量达到最大，其磁矩的改变量也达到最大。