Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session A09: Ferroic oxides - Domain and Domain WallsFocus
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Sponsoring Units: DMP Chair: Seiji Kojima, University of Tsukuba Room: LACC 301A |
Monday, March 5, 2018 8:00AM - 8:12AM |
A09.00001: Domain boundaries in hybrid improper ferroelectric layered perovskites Elizabeth Nowadnick Coupling or competition between spin, charge, orbital, and structural order parameters can lead to novel properties and functionality in materials. In the hybrid improper ferroelectric n=2 Ruddlesden-Popper oxides, the polarization is coupled to two octahedral rotation distortions of different symmetries. This coupling not only enables new functionality, but also stabilizes a fascinating domain topology of different types of domain boundaries coupled together at domain wall vortices and antivortices. However, the precise way in which the multiple order parameters in hybrid improper ferroelectrics evolve across the domain boundaries, and their atomic-scale structure, is still an open question. In this talk, I will utilize a combination of group theoretic methods, Landau theory, and density functional theory calculations to present scenarios for the local structure at domain boundaries in the hybrid improper ferroelectric Ca3Ti2O7 and related A3B2O7 materials. |
Monday, March 5, 2018 8:12AM - 8:24AM |
A09.00002: An analysis of the symmetry evolution and domain structure in RbFe(MoO4)2 near its ferroaxial phase transition Wencan Jin, Elizabeth Drueke, Kara Mattioli, Siwen Li, Alemayehu Admasu, Jae Wook Kim, Yazhong Wang, Sang-Wook Cheong, Liuyan Zhao The physics of frustrated magnets can be modeled as a two-dimensional triangle lattice antiferromagnet (2D TLA). One of the first such 2D TLA candidates discovered was RbFe(MoO4)2. Interest in this material has recently been renewed due to the discovery of ferroelectricity in the vicinity of antiferromagnetism (AFM) around 3.8K, which leads to a multiferroic state. The magnetic structure of RbFe(MoO4)2 has a structural phase transition at temperature TC≈190K which leads to a ferroaxial magnetic structure, but the nature of this ferroaxial phase transition and its domain distribution are not yet know. This is important because current understanding of the ferroelectricity in RbFe(MoO4)2 depends on the AFM order hosted on the ferroaxial crystal lattice. In this talk, I present an analysis using an ultrafast rotation anisotropy and second harmonic generation (RA-SHG) experiment to investigate the symmetry evolution around TC and wide-field SHG imaging to resolve the domain distribution of the ferroaxial structure order. |
Monday, March 5, 2018 8:24AM - 8:36AM |
A09.00003: Evolution of a1/a2 Domains in Strained Ferroelectric Thin Films Desheng Ma, Lixin Yang, Yinlian Zhu Ferroelectric domains are of great importance in both scientific and application aspects [1]. Tailoring their novel configurations and understanding their structural evolution are crucial to better controlling the domain configurations for future devices. We grow ferroelectric PbTiO3 films with various thicknesses on scandate substrates by Pulsed Laser Deposition (PLD) technique. By means of Cs-corrected Transmission Electron Microscopy (TEM) , the domain structures were characterized in PbTiO3 thin films. It is found that PbTiO3 films grown on SmScO3 substrates are domain oriented consisting of dominant a1/a2 domains. The a1/a2 domains distribute periodically and the width increases with increasing film thickness. Further increasing film thickness, a/c domains appear. The critical thickness for the formation of a1/a2 domains is around 2 nm. Cs-corrected STEM imaging demonstrates that the domain walls of a1/a2 domain structure have the rotation characteristic of 90° ferroelastic domain wall. |
Monday, March 5, 2018 8:36AM - 8:48AM |
A09.00004: Self-strain-induced fragmentation of Z8 vortex domains in (Nd,Tb,Sr)3Fe2O7 Fei-Ting Huang, Yanbin Li, Lunyong Zhang, Jae Wook Kim, Yazhong Wang, Kai Du, Sang-Wook Cheong (Nd,Tb,Sr)3Fe2O7 crystals, n=2 Ruddlesden-Popper ferrite, exhibit dense networks of topological defects (eight-state vortex-antivortex pairs), associated with four oxygen octahedral tilts at domains and another four different oxygen octahedral tilts at domain walls. Here, utilizing dark-field transmission electron microscopy (TEM), we show experimentally that the formation of eight-state vortex domains follows a universal behavior captured within the Kibble-Zurek scaling mechanism. In addition, a self-strain-induced fragmentation of such vortex domains occurs when long-range ferroelastic couplings become dominant. We develop a complete picture of the topological defect evolution through 1st-order and 2nd-order phase transitions, affecting significantly the condensation of topological defect types. How the resulting microscopic domain structures influence macroscopically phenomena will also be discussed. |
Monday, March 5, 2018 8:48AM - 9:00AM |
A09.00005: Universality of Topological Vortex Domains in Layered Perovskites Sang-Wook Cheong, Fei-Ting Huang, Bin Gao In numerous functional materials, such as steels, ferroelectrics and magnets, new functionalities can be achieved through the engineering of the domain structures, which are associated with the ordering of certain parameters within the material. The recent progress in technologies that enable imaging at atomic-scale spatial resolution has transformed our understanding of domain topology: along with simple stripe-like or irregularly shaped domains, intriguing vortex-type topological domain configurations often appear in complex materials. It turns out that vortex domains are rather common in layered perovskites such as Ca3-xSrxTi2O7. In Ca3-xSrxTi2O7, the vortex domain formation, associated with the existence of abundant Néel-type ferroelectric walls, results in the presence of numerous conducting charged walls. The relationship between two distinct vortex domains and the emergence of polar-antipolar order at domain walls will be also discussed. |
Monday, March 5, 2018 9:00AM - 9:12AM |
A09.00006: Improper Ferroelectricity at antiferromagnetic domain walls of Perovskite oxides Wei Ren, Yali Yang SmFeO3 (SFO) was reported to present ferroelectric order at high temperature 670 K, an effect which is still unclear and under debate. We are motivated to explore if a specific mechanism can generate an electrical polarization in SmFeO3 or, more generally, in perovskites possessing magnetic ordering. In this work, first-principles calculations have been performed on a variety of (initially paraelectric) Xn-m magnetic multidomains in SmFeO3, with X= G, C, A or F being the predominant magnetic ordering existing inside each domain. These calculations allow us to reveal that (i) domains with even n and m integers become polar and thus multiferroic, with a polarization pointing along the b-axis; (ii) the polarization of these even n and m domains decreases as the sum of n and m increases for a given predominant magnetic ordering X; and (iii) this improper polarization is related to the motions of oxygen ions at the domain walls. A unified model for the spin-order induced ferroelectricity demonstrates that the polarization arises from symmetric magnetic exchange striction interactions due to magnetic domain walls. |
Monday, March 5, 2018 9:12AM - 9:48AM |
A09.00007: Athermal domain-wall creep near a ferroelectric quantum critical point Invited Speaker: Fumitaka Kagawa Ferroelectric domain walls that separate regions with distinct electric-polarization directions are typically stationary because of the presence of a pinning potential. Nevertheless, thermally activated, irreversible creep motion can occur under a moderate electric field, thereby underlying rewritable and non-volatile memory applications. Conversely, as the temperature decreases, the occurrence of creep motion becomes less likely and eventually impossible under realistic electric field magnitudes. Here, we show that such frozen ferroelectric domain walls recover their mobility under the influence of quantum fluctuations. Non-linear permittivity and polarization retention measurements of an organic charge-transfer complex reveal that ferroelectric domain-wall creep occurs via an athermal process when the system is tuned close to a pressure-driven ferroelectric quantum critical point (QCP). Despite the heavy masses of material building blocks such as molecules, the estimated effective mass of the domain wall is comparable to the proton mass, indicating the realization of a ferroelectric domain wall with a quantum-particle nature near the QCP [1]. |
Monday, March 5, 2018 9:48AM - 10:00AM |
A09.00008: Dielectric Properties of Relaxor-based Ferroelectrics with Landau-Ginzburg-Devonshire Theory and Domain Effects Masahito Sayanagi, Julian Irwin, Shane Lindemann, Chang-Beom Eom, Mark Rzchowski Magnetoelectric coupling observed in relaxor-based ferroelectrics makes them attractive for a wide variety of sensing and information technology applications. We study the polarization dynamics and dielectric properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) thin films grown by RF sputter deposition. Using independent polarization and permittivity measurements, we analyze the permittivity as a function of the polarization, and compare to behavior extracted from Landau-Ginzburg-Devonshire theory in single and multiple domain models. We use this to determine the electric field and polarization ranges dominated by single and multiple domain effects, and investigate the electric field dependence of the permittivity, and the effect on magnetoelectric coupling. We also examine the effect of crystallographic orientation on the dielectric properties. |
Monday, March 5, 2018 10:00AM - 10:12AM |
A09.00009: Domain walls in strontium titanate C Stephen Hellberg, Madeleine Phillips The crystal structure of SrTiO3 transforms below 105 K from cubic to tetragonal. An applied gate voltage can be used to move the domains in samples with a thin epitaxial LaAlO3 film. We present the atomic and electronic structure of domain walls in SrTiO3 based on density functional calculations. We compute the effects of a LaAlO3 film on the domains at the interface. We examine how doping at the interface modifies the domain structure. The importance of domains on electron pairing without superconductivity in this system will be discussed. |
Monday, March 5, 2018 10:12AM - 10:24AM |
A09.00010: Structural Dynamics and Electrical Conduction of Ferroelectric Domain Walls in Hexagonal (Sc,Lu)FeO3 Xiaoyu Wu, Kai Du, Lu Zheng, Di Wu, Sang-Wook Cheong, Keji Lai Electrical conduction due to mobile carriers in ferroelectric domains and domain walls has been extensively studied in recent years for their potential applications in nano-electronics. On the other hand, the dielectric loss due to dipolar relaxation and domain wall oscillations is of paramount important for ferroelectric devices working at radio and microwave frequencies. Using a combination of conductive atomic force microscopy (C-AFM) and scanning microwave impedance microscopy (MIM), we demonstrate the local conductivity mapping at both dc and GHz frequencies in hexagonal (Sc,Lu)FeO3 single crystals. Interestingly, while free carriers are responsible for the contrast observed at oppositely polarized domains, the MIM signals at the DWs are clearly dominated by a localized vibrational mode. In particular, the effective GHz conductivity of the DWs, which shows little dependence on the tip bias, is 2 ~ 3 orders of magnitude higher than that at zero-frequency. Our results provide new impetus to incorporate the nanometer-sized ferroelectric DWs into novel high-frequency devices. |
Monday, March 5, 2018 10:24AM - 10:36AM |
A09.00011: Polarization Switching Kinetics in Si Doped HfO2 Thin Films Tae Yoon Lee, KyoungJun Lee, Seung Chae Recently, HfO2 based ferroelectric thin films have attracted attention as a promising candidate for ferroelectric random access memories (FRAM). A lot of researches demonstrated robust ferroelectricity with large polarization value comparable with conventional ferroelectric perovskites, e. g., BaTiO3. In addition, an enhancement of remnant polarization, namely, wake-up effect was reported after external electric field cycling which usually cause the decrease of remnant polarization. Elucidation of ferroelectric switching dynamics is required to clarify an underlying mechanism for practical device applications. |
Monday, March 5, 2018 10:36AM - 10:48AM |
A09.00012: Nonvolatile Memory based on Reconfigurable Ferroelectric Domain Walls Pankaj Sharma, Qi Zhang, Daniel Sando, Chi-Hou Lei, Yunya Liu, Jiangyu Li, Valanoor Nagarajan, Jan Seidel Interfaces and boundaries between competing phases and materials have gathered immense interest as potential nanoelectronic elements. IBM is currently developing ‘race-track memories’ in which the high-density digital information is encoded in the form of magnetic domain walls, which can be injected and moved controllably along 3 dimensional ferromagnetic nanowires. Only recently, analogous research in ferroelectric materials has seen tremendous interest, because of much smaller domain wall sizes and the potential of electric field induced wall movement that could enable ultralow-power electronics. |
Monday, March 5, 2018 10:48AM - 11:00AM |
A09.00013: Electric Configuration of the Topological Textures in a Ferroelectric Nanoplate by Partial Domain Switching Kwangeun Kim, Seuri Jeong, Kanghyun chu, Jin Hong Lee, Gi-Yeop Kim, Fei Xue, Tae-Yeong Koo, Long-Qing Chen, Si-Young Choi, Ramamoorthy Ramesh, Chan-Ho Yang Vortices in ferroic materials have not only provided a new perspective for describing collective orders in matter but also given potential applications for high density non-volatile information storage. However, creation of stable isolate ferroelectric vortex states and electric configuration of the topological invariant in dielectrics are experimentally still veiled. Here, we show an epitaxial ferroelectric square nanoplate of bismuth ferrite subject to a large strain gradient associated with misfit strain relaxation enables five discrete levels for the ferroelectric topological invariant of the entire system as a consequence of the peculiar radial strain relaxation and the domain wall chirality. The total winding number of the nanoplate can be configured from -1 to 3 by selective non-local electric switching of the radial-quadrant domains. By using position-sensitive angle-resolved piezoresponse force microscopy, we directly identify the existence of vortices and anti-vortices, observe pair creation and annihilation, and manipulate the total net number of vortices. Our findings offer a useful concept to stabilize and control the ferroelectric vortices for multi-level topological defect memory. |
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