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Exploration of topological defects in ferroelectrics

铁电体拓扑缺陷的探索

基本信息

批准号：
2279492
负责人：
金额：
--
依托单位：
Queen's University Belfast
依托单位国家：
英国
项目类别：
Studentship
财政年份：
2019
资助国家：
英国
起止时间：
2019 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=studentship-2279492
关键词：
Exploration topological defects ferroelectrics

项目摘要

Ferroelectrics (FEs) are materials which exhibit spontaneous polarisation below a certain temperature, and have two or more stable polarisation states, reversibly accessible by application of external fields. Previous applications have involved domains -regions of the FE with a consistent sense of polarisation- as the functional part of the material. Recent focus has switched to the domain walls (DWs), the nanoscale membrane-like structures that separate domains. DWs have been shown to exhibit properties distinct from the domains surrounding them. This project aims to investigate two areas of this evolving field: domain wall conduction and FE skyrmions.Enhanced electrical conductivity at DWs in an otherwise insulating bulk(1) has now been demonstrated in many materials. Also, since the polarisation is reversible with the application of external fields, DWs can be moved and controlled, even created and removed, giving rise to the idea of a new kind of reconfigurable circuitry, where the domain wall is a mobile electrical connection(2). Conduction varies, but characterising the conduction is key to realising domain wall nanoelectronics, and is one of the main aims of the project. Work is under way to obtain a measurement for the carrier mobility of conducting DWs in lithium niobate (LN) by measuring the geometric magnetoresistance- a change in resistivity upon application of a magnetic field. This effect arises due to the unique conical geometry of the DWs that can be written in LN thin films(1), making a novel measurement of mobility in domain walls possible. Furthermore, plans are in place to make some of the first direct measurements of the electronic band structure specifically at conducting DWs. Using a large facility X-Ray source to excite carriers locally at the DWs, energy and momentum of carriers can be measured. These parameters comprise the electronic band structure, giving insight into the mechanism behind the enhanced conductivity.Another aspect of the project is to investigate a FE analogy to the magnetic skyrmion. A magnetic skyrmion is a confined spin pattern, described as being 'topologically protected', meaning it cannot be continuously deformed and removed, and is somewhat stable. Their promise comes from their nanometer size, making them ideal for high density data storage applications, such as the recently envisioned racetrack memory(3). An electric counterpart, where polarisation replaces spin, has been theoretically predicted(4) and observed(5) in complex structures, but the general case is yet to be seen(4). If found, FE skyrmions could be controlled by fields in a similar way to the DWs mentioned above, and thus hold promise as functional elements(4). This project seeks to use focussed ion beams to cut thin slices of FE lead titanate, write a domain pattern which is expected to be skyrmionic, and use atomic resolution transmission electron microscopy (in collaboration with University of Limerick), to verify this. If observed, we could move forward into using novel atomic force microscopy methods to write, move and control these polarisation patterns with applied fields, investigating their response and transport properties, exploring their physical origin and ultimately characterising them for potential application.1. Schröder, Mathias, et al. "Conducting domain walls in lithium niobate single crystals." Advanced Functional Materials 22.18 (2012): 3936-3944.2. McQuaid, Raymond GP, et al. "Injection and controlled motion of conducting domain walls in improper ferroelectric Cu-Cl boracite." Nature communications 8 (2017): 15105.3. Tomasello, Riccardo, et al. "A strategy for the design of skyrmion racetrack memories." Scientific reports 4 (2014): 6784.4. Gonçalves, MA Pereira, et al. "Theoretical guidelines to create and tune electric skyrmion bubbles." Science advances 5.2 (2019):eaau7023.5. Das, Sujit, et al. "Observation of room-temperature polar skyrmions." Nature 568.7752 (2019): 368.

铁电体（FE）是在一定温度以下表现出自发极化的材料，并且具有两个或更多个稳定的极化状态，通过施加外部场可逆地可访问。以前的应用涉及域-具有一致偏振感的FE区域-作为材料的功能部分。最近的焦点转向了畴壁（DWs），即分隔畴的纳米级膜状结构。DWs已经显示出与其周围的域不同的特性。本项目旨在研究这一不断发展的领域的两个领域：畴壁传导和FE skyrmions。在绝缘体中的DW处增强的电导率（1）现在已经在许多材料中得到证实。此外，由于极化在施加外部场的情况下是可逆的，所以DW可以被移动和控制，甚至被创建和移除，从而产生了一种新的可重构电路的想法，其中畴壁是移动的电连接（2）。传导各不相同，但表征传导是实现畴壁纳米电子学的关键，也是该项目的主要目标之一。目前正在开展工作，通过测量几何磁阻-施加磁场后电阻率的变化-来测量锂酸盐（LN）中导电DW的载流子迁移率。这种效应是由于可以写入LN薄膜中的DW的独特圆锥形几何形状而产生的（1），从而使畴壁中的迁移率的新测量成为可能。此外，还计划对电子能带结构进行一些首次直接测量，特别是在传导DW处。利用一个大型的X射线源在DW上局部激发载流子，可以测量载流子的能量和动量。这些参数组成了电子能带结构，使我们能够深入了解导电性增强背后的机制。该项目的另一个方面是研究与磁skyrmion的FE类比。磁skyrmion是一种受限的自旋模式，被描述为“拓扑保护”，这意味着它不能连续变形和移除，并且有点稳定。它们的承诺来自于它们的纳米尺寸，使它们成为高密度数据存储应用的理想选择，例如最近设想的赛道存储器（3）。在复杂结构中，已经在理论上预测（4）和观察（5）了一个电对应物，其中极化取代了自旋，但一般情况还有待观察（4）。如果发现，FE skyrmions可以通过类似于上述DW的方式由场控制，因此有望作为功能元素（4）。该项目旨在使用聚焦离子束切割FE钛酸铅薄片，写入预期为skyrmionic的畴图案，并使用原子分辨率透射电子显微镜（与利默里克大学合作）来验证这一点。如果被观察到，我们可以使用新的原子力显微镜方法来写入，移动和控制这些偏振模式，研究它们的响应和传输特性，探索它们的物理起源，并最终表征它们的潜在应用。Schröder，Mathias等人，《锂酸盐单晶中的导电畴壁》。“Advanced Functional Materials 22.18（2012）：3936-3944.2. McQuaid，Raymond GP等人，“在不适当的铁电Cu-Cl硼酸盐中导电畴壁的注入和受控运动。《自然通讯》8（2017）：15105.3。Tomasello，Riccardo，et al.“A strategy for the design of skyrmion racetrack memories.科学报告4（2014）：6784.4。Gonçalves，MA佩雷拉等人，“创建和调整电skyrmion气泡的理论指南。科学进展5.2（2019）：eaau7023.5。Das，Sujit，et al.“Observation of room-temperature polar skyrmions.《自然》568.7752（2019）：368。

项目成果

期刊论文数量（7）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

Anisotropic, meandering domain microstructure in the improper ferroelectric CsNbW2O9

DOI：
10.1063/5.0026040
发表时间：
2020-10
期刊：
APL Materials
影响因子：
6.1
作者：
S. McCartan;P. Turner;J. A. McNulty;J. R. Maguire;C. J. McCluskey;F. Morrison;J. Gregg;I. MacLaren
通讯作者：
S. McCartan;P. Turner;J. A. McNulty;J. R. Maguire;C. J. McCluskey;F. Morrison;J. Gregg;I. MacLaren

Polarization Topology at the Nominally Charged Domain Walls in Uniaxial Ferroelectrics