Intrinsic and extrinsic effects on the electrotoroidic switching in a ferroelectric notched nanodot by a homogeneous electric field
Intrinsic and extrinsic effects on the electrotoroidic switching in a ferroelectric notched nanodot by a homogeneous electric field
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DOI：
10.1039/c9cp04676c
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发表时间：
2019-12-07
影响因子：
3.3
通讯作者：
Kitamura, Takayuki
中科院分区：
文献类型：
--
作者：
Hai Dinh-Van;Le Van Lich;Kitamura, Takayuki
铁电体中拓扑缺陷的控制，特别是通过均匀电场的控制，已经成为一个活跃的研究方向。极化涡旋是铁电纳米点中形成的一种基本拓扑缺陷，最近已被证明可以通过使用低对称性纳米点控制内置电分布来由均匀电场进行切换。这种电转矩开关被研究用于接近理想的系统，例如，独立的纳米点。然而，电致伸缩开关可能受到几个因素的影响，例如，挠曲电的纳米级效应（本征效应）、外延应变和施加场的频率（非本征效应）。在本研究中，研究了均匀电场下缺口纳米点中极化涡旋的开关。重点比较了内、外效应对涡旋开关的影响。结果表明，由于切口的出现，涡旋开关通过交替的涡旋-极性和极性-涡旋转换发生。虽然挠曲电性在极化转变过程中破坏了缺口纳米点中极化场的对称性，并引起了偏离缺口纳米点对称轴的涡核的不寻常行为，但这种内在效应在极化涡的切换行为中起着相对不显著的作用。与本征效应相比，有趣的是，非本征效应强烈地影响着涡旋的切换行为。具体地，所施加的电场的频率可以改变环形磁滞回线的形状和涡旋切换的域变换过程。此外，在衬底约束下，发生涡旋-极性和极性-涡旋转变的矫顽电场的大小随着应变的增加而线性减小。本研究提供了有益的信息，有效地控制偏振涡，这是由外在因素，而不是内在的。
The control of topological defects in ferroelectrics, in particular by a homogeneous electric field, has emerged as an active research direction. A polarization vortex, which is a fundamental topological defect formed in ferroelectric nanodots, has recently been demonstrated to be switchable by a homogeneous electric field through the control of the built-in electrical distribution using low-symmetry nanodots. Such electrotoroidic switching is investigated for nearly ideal systems, e.g., free-standing nanodots. However, the electrotoroidic switching may be impacted by several factors, for instance, the nanoscale effect of flexoelectricity (intrinsic effect), epitaxial strain and the frequency of the applied field (extrinsic effects). In the present study, the switching of the polarization vortex in a notched nanodot under a homogeneous electric field is investigated. The emphasis is put on a comparison between intrinsic and extrinsic effects on the vortex switching. The results show that the vortex switching takes place through alternate vortex-to-polar and polar-to-vortex transformations due to the appearance of the notch. Although the flexoelectricity breaks the symmetry of the polarization field in the notched nanodot during the polarization transformation and gives rise to an unusual behavior of the vortex core, which departs from the symmetry axis of the notched nanodot, this intrinsic effect plays a relatively insignificant role in the switching behavior of the polarization vortex. In comparison to the intrinsic effect, interestingly, the extrinsic effects strongly influence the vortex switching behavior. Specifically, the frequency of the applied electric field can alter both the shape of the toroidal hysteresis loop and the domain transformation process of the vortex switching. In addition, under substrate constraints, the magnitude of the coercive electric fields at which the vortex-to-polar and polar-to-vortex transformations occur linearly decreases with the increase of strain. The present study provides instructive information on the efficient control of a polarization vortex, which is dominated by extrinsic factors rather than intrinsic ones.