Asymmetric flux-closure domains in compositionally graded nanoscale ferroelectrics and unusual switching of toroidal ordering by an irrotational electric field
Asymmetric flux-closure domains in compositionally graded nanoscale ferroelectrics and unusual switching of toroidal ordering by an irrotational electric field
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DOI：
10.1016/j.actamat.2019.08.025
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发表时间：
2019-10-15
期刊：
影响因子：
9.4
通讯作者：
Van-Hai Dinh
中科院分区：
文献类型：
--
作者：
Le Van Lich;Minh-Tien Le;Van-Hai Dinh
铁电纳米结构中的反转极化涡旋畴对于下一代电子纳米器件具有重要作用。然而，在铁电体中的极化涡旋状域的直接切换是一个不平凡的任务，因为环向力矩是共轭的卷曲电场，而不是均匀的。这项工作是致力于开发一种方法，直接开关的环形有序下的无旋（均匀）电场与使用成分梯度铁电（cgFE）纳米点。材料组成的变化诱导了额外的空间反转对称性在超越晶胞水平的尺度上被破坏，从而导致在cgFE纳米点中形成不对称的磁通闭合域（FCD）。更有趣的是，这种非对称特性有助于通过无旋电场实现FCD的开关。特别地，极化的旋转可以直接从逆时针旋转切换到顺时针旋转，反之亦然，而在切换过程期间不形成中间畴结构。这种切换行为是区别于同质同行。我们进一步证明，材料成分的变化剪裁的静电和总自由能的分布在cgFE纳米点，可以控制湮灭/引发过程下的无旋电场FCD，提供了根本原因的直接切换的环矩。另一个有趣的问题是，发现施加的电场的幅度和频率强烈影响FCD在cgFE纳米点的开关行为。(C)2019 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
A reversal of polarization vortexlike domains in ferroelectric nanostructures plays important roles for next generations of electronic nanodevices. However, a direct switching of the polarization vortexlike domains in ferroelectrics is a nontrivial task since the toroidal moment is conjugated to a curled electric field rather than a homogeneous one. This work is dedicated to developing an approach to directly switch the toroidal ordering under an irrotational (homogeneous) electric field with the use of compositionally graded ferroelectric (cgFE) nanodots. The variation in material compositions induces an additionally broken spatial inversion symmetry at a scale beyond unit-cell level, giving rise to a formation of asymmetric flux-closure domain (FCD) in a cgFE nanodot. More interestingly, such an asymmetric character facilitates to a switch of FCD by an irrotational electric field. In particular, the rotation of polarization can be directly switched from counter-clockwise to clockwise rotations and vice versa without a formation of intermediate domain structures during the switching process. This switching behavior is distinguished from that in homogeneous counterparts. We further demonstrate that the variation in material compositions tailors the distributions of electrostatic and total free energies in the cgFE nanodot that can control the annihilation/initiation process of FCD under irrotational electric field, providing fundamental reason for the direct switching of the toroidal moment. Another interesting issue is found that both the amplitude and frequency of applied electric field strongly affect the switching behavior of FCD in cgFE nanodot. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.