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1. Domain-wall magnetoelectric coupling in multiferroic hexagonal YbFeO3 films

   https://doi.org/10.1038/s41598-023-28365-x  

   Li, Xin; Yun, Yu; Thind, Arashdeep Singh; Yin, Yuewei; Li, Qiang; Wang, Wenbin; N’Diaye, Alpha T.; Mellinger, Corbyn; Jiang, Xuanyuan; Mishra, Rohan; et al (December 2023, Scientific Reports)

   Abstract Electrical modulation of magnetic states in single-phase multiferroic materials, using domain-wall magnetoelectric (ME) coupling, can be enhanced substantially by controlling the population density of the ferroelectric (FE) domain walls during polarization switching. In this work, we investigate the domain-wall ME coupling in multiferroic h-YbFeO₃thin films, in which the FE domain walls induce clamped antiferromagnetic (AFM) domain walls with reduced magnetization magnitude. Simulation according to the phenomenological theory indicates that the domain-wall ME effect is dramatically enhanced when the separation between the FE domain walls shrinks below the characteristic width of the clamped AFM domain walls during the ferroelectric switching. Experimentally, we show that while the magnetization magnitude remains same for both the positive and the negative saturation polarization states, there is evidence of magnetization reduction at the coercive voltages. These results suggest that the domain-wall ME effect is viable for electrical control of magnetization. 

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2. Polarization pinning at antiphase boundaries in multiferroic YbFeO ₃

   https://doi.org/10.1088/1674-1056/ad8cbc  

   Ren, Guodong; Omprakash, Pravan; Li, Xin; Yun, Yu; Thind, Arashdeep S; Xu, Xiaoshan; Mishra, Rohan (November 2024, Chinese Physics B)

   Abstract The switching characteristics of ferroelectrics and multiferroics are influenced by the interaction of topological defects with domain walls. We report on the pinning of polarization due to antiphase boundaries in thin films of the multiferroic hexagonal YbFeO₃. We have directly resolved the atomic structure of a sharp antiphase boundary (APB) in YbFeO₃thin films using a combination of aberration-corrected scanning transmission electron microscopy (STEM) and total energy calculations based on density-functional theory (DFT). We find the presence of a layer of FeO₆octahedra at the APB that bridges the adjacent domains. STEM imaging shows a reversal in the direction of polarization on moving across the APB, which DFT calculations confirm is structural in nature as the polarization reversal reduces the distortion of the FeO₆octahedral layer at the APB. Such APBs in hexagonal perovskites are expected to serve as domain-wall pinning sites and hinder ferroelectric switching of the domains. 

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3. Electronic structure orientation as a map of in-plane antiferroelectricity in β′-In ₂ Se ₃

   https://doi.org/10.1126/sciadv.ado2136  

   Spellberg, Joseph L; Kodaimati, Lina; Joshi, Prakriti P; Mirzajani, Nasim; Liang, Liangbo; King, Sarah B (June 2024, Science Advances)

   Antiferroelectric (AFE) materials are excellent candidates for sensors, capacitors, and data storage due to their electrical switchability and high-energy storage capacity. However, imaging the nanoscale landscape of AFE domains is notoriously inaccessible, which has hindered development and intentional tuning of AFE materials. Here, we demonstrate that polarization-dependent photoemission electron microscopy can resolve the arrangement and orientation of in-plane AFE domains on the nanoscale, despite the absence of a net lattice polarization. Through direct determination of electronic transition orientations and analysis of domain boundary constraints, we establish that antiferroelectricity in β′-In₂Se₃is a robust property from the scale of tens of nanometers to tens of micrometers. Ultimately, the method for imaging AFE domain organization presented here opens the door to investigations of the influence of domain formation and orientation on charge transport and dynamics. 

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4. Influence of oxygen vacancies on the domain wall stability in BiFeO ₃

   https://doi.org/10.1111/jace.19752  

   Zhang, Mao‐Hua; Tan, Yueze; Yang, Tiannan; Chen, Long‐Qing (February 2024, Journal of the American Ceramic Society)

   Abstract Oxygen vacancy is the most common type of point defects in functional oxides, and it is known to have profound influence on their properties. This is particularly true for ferroelectric oxides since their interaction with ferroelectric polarization often dictates the ferroelectric responses. Here, we study the influence of the concentration of oxygen vacancies on the stability of ferroelectric domain walls (DWs) in BiFeO₃, a material with a relatively narrow bandgap among all perovskite oxides, which enables strong interactions among electronic charge carriers, oxygen vacancies, and ferroelectric domains. It is found that the electronic charge carriers in the absence of oxygen vacancies have essentially no influence on the spatial polarization distribution of the DWs due to their low concentrations. Upon increasing the concentration of oxygen vacancies, charge‐neutral DWs with an originally symmetric polarization distribution symmetric around the center of the wall can develop a strong asymmetry of the polarization field, which is mediated by the electrostatic interaction between polarization and electrons from the ionization of oxygen vacancies. Strongly charged head‐to‐head DWs that are unstable without oxygen vacancies can be energetically stabilized in the off‐stoichiometric BiFeO_3−δwithδ∼ 0.02 where ionization of oxygen vacancies provides sufficient free electrons to compensate the bound charge at the wall. Our results delineate the electrostatic coupling of the ionic defects and the associated free electronic charge carriers with the bound charge in the vicinity of neutral and charged DWs in perovskite ferroelectrics. 

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5. A Predictive Theory for Domain Walls in Oxide Ferroelectrics Based on Interatomic Interactions and its Implications for Collective Material Properties

   https://doi.org/10.1002/adma.202106021  

   Samanta, Atanu; Yadav, Suhas; Gu, Zongquan; Meyers, Cedric_J G; Wu, Liyan; Chen, Dongfang; Pandya, Shishir; York, Robert A; Martin, Lane W; Spanier, Jonathan E; et al (February 2022, Advanced Materials)

   Abstract Domain walls separating regions of ferroelectric material with polarization oriented in different directions are crucial for applications of ferroelectrics. Rational design of ferroelectric materials requires the development of a theory describing how compositional and environmental changes affect domain walls. To model domain wall systems, a discrete microscopic Landau–Ginzburg–Devonshire (dmLGD) approach with A‐ and B‐site cation displacements serving as order parameters is developed. Application of dmLGD to the classic BaTiO₃, KNbO_3,and PbTiO₃ferroelectrics shows that A–B cation repulsion is the key interaction that couples the polarization in neighboring unit cells of the material. dmLGD decomposition of the total energy of the system into the contributions of the individual cations and their interactions enables the prediction of different properties for a wide range of ferroelectric perovskites based on the results obtained for BaTiO₃, KNbO_3,and PbTiO₃only. It is found that the information necessary to estimate the structure and energy of domain‐wall “defects” can be extracted from single‐domain 5‐atom first‐principles calculations, and that “defect‐like” domain walls offer a simple model system that sheds light on the relative stabilities of the ferroelectric, antiferroelectric, and paraelectric bulk phases. The dmLGD approach provides a general theoretical framework for understanding and designing ferroelectric perovskite oxides. 

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