Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y70: New Order in Ferroelectrics and MultiferroicsFocus Recordings Available
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Sponsoring Units: DMP Chair: Minseong Lee, Los Alamos National Lab Room: Hyatt Regency Hotel -Jackson Park B |
Friday, March 18, 2022 8:00AM - 8:36AM |
Y70.00001: Exploring non-collinear magnetic textures in multiferroics Invited Speaker: Bertrand Dupé Magnetic skyrmions are localized, non-collinear chiral magnetic textures which are envisioned to play a major role in spintronics [1] and neuromorphic computing [2] applications. Thanks to their topological properties that enhance their stability, ferromagnetic (FM) skyrmions in metals have been the subject of intense research in metals since the last 10 years. |
Friday, March 18, 2022 8:36AM - 8:48AM |
Y70.00002: A new antiferroelectric ground state for PbZrO3 and PbHfO3: dipolar vortices and octahedral super-tilting versus quantum suppression Jack S Baker, David R Bowler, Mike Glazer, Bin Xu, Gustau Catalan, Roman Burkovsky, Kane Shenton, Pablo Vales-Castro, Jirka Hlinka, Pavel Marton, Marek Pasciak, Krystian Roleder, Nan Zhang PbZrO3 and PbHfO3 are still considered the antiferroelectric (AFE) archetypes despite their shared complex crystal structure and plethora unresolved questions regarding the paraelectric to AFE phase transition. In this work, we question the the nature of the ground state AFE phase of both materials. That is, first principles density functional theory (DFT) simulations of AFE PbZrO3 and PbHfO3 reveal a dynamical instability in the phonon spectra of their purported low temperature Pbam ground states. This instability doubles the c-axis of Pbam and condenses five new small amplitude phonon modes giving rise to an 80-atom Pnam structure. Compared with Pbam, the stability of this new structure is slightly enhanced and highly reproducible as demonstrated through using different DFT codes and different treatments of electronic exchange & correlation interactions. Remarkably, one unstable mode condenses dipolar vortex-antivortex pairs reminiscent of those observed in PbTiO3/SrTiO3 superlattices and ultrathin PbTiO3 films. Our findings suggest one of three things: (i) Pnam is the correct space-group below the AFE phase transition temperature and previous assignments were incomplete, missing small amplitude symmetry-breaking components (ii) Pnam is the result of a new transition at super-cryogenic temperatures or, most likely, (iii) these new phonon modes are suppressed by quantum fluctuations making PZO and PHO members of a class of quantum suppressed crystals. We rationalize each of these possibilities through pairing experimental and theoretical arguments. With this Pnam phase, we bring parity between the supposed AFE archetypes and recent observations of a very similar phase in doped or electrostatically engineered BiFeO3. |
Friday, March 18, 2022 8:48AM - 9:00AM |
Y70.00003: Flexoelectricity in Antiferromagnetic Nickel Oxide John Cavin, James M Rondinelli Flexoelectricity describes the coupling between electric polarization and strain gradient. Because it is represented by a rank 4 tensor, it is not prohibited by the presence of inversion symmetry in a crystal in the same way as piezoelectricity. Despite being a ubiquitous phenomenon among dielectric materials, the set of materials whose flexoelectric effects have been studied is sparse. Here, we present a first-principles study on the flexoelectric coupling of antiferromagnetic NiO. We employ density functional perturbation theory to probe its bulk flexoelectric effect and utilize a recently developed technique to examine the mean-inner-potential contribution to flexoelectricity [1]. We report on magnetic contributions to the flexoelectric response in NiO and the possibility of a spin-polarized flexoelectric tensor. In addition to the applications of NiO in flexoelectric nanogenerators, we describe the relevance of flexoelectricity to corrosion of Ni-based alloys. |
Friday, March 18, 2022 9:00AM - 9:12AM Withdrawn |
Y70.00004: Flexoelectricity and Ferroelectric Domain Walls: Landau Theory from Density-Functional Theory Calculations Oswaldo Dieguez, Massimiliano Stengel Domain walls between two ferroelectric regions of a perovskite oxide with antiparallel polarization vectors are, in many of these materials, atomically thin. Despite of this, simple continuum Landau models where a thermodynamic potential is expanded as a function of strain, polarization, and the gradient of polarization give good predictions of wall energy, wall thickness, and atomic displacements. In the work presented in this talk, we developed Landau models for six different perovskites and we computed the coefficients of those models, some of which are related to the flexoelectric properties of the oxide. In the process, we addressed the role of some arbitrary choices that one faces regarding the definition of local strain, polar distortion pattern, and flexoelectric tensor, which have an impact in the predictions of the model---and we describe criteria that ensure physically meaningful results. We finally show that the solutions produced in this way agree very well with our full density-functional theory calculations. |
Friday, March 18, 2022 9:12AM - 9:24AM |
Y70.00005: Lattice Distortions and Ferroelectricity in Antiperovskites and Antiperovskite-like Structures He Zhu, Turan Birol Perovskite and perovskite-like ferroelectrics have been intensively studied owing to their promising applications in modern electronic devices. However, with the same crystal structure and assumably similiar versatility, antiperovskites were rarely reported as potential ferroelectrics. In this work, we study structural instabilities of a series of tetrel antiperovskite oxides A3TtO (A = Ca, Sr, Ba; Tt = Si, Ge, Sn, Pb), as well as corresponding inverse double perovskites A6Tt'TtO2. Using first principles Density Functional Theory (DFT) calculations, we show that improper ferroelectricity induced by octahdedral rotations in layered inverse double perovskites is achievable, and that the dependence of the ferroelectric polarization on the tolerance factors of the parent phases displays trends similar to those observed in regular perovskite oxide heterostructures. |
Friday, March 18, 2022 9:24AM - 9:36AM |
Y70.00006: Direct observation of polar/non-polar phase coexistence in Ca2.9Sr0.1Mn2O7 Kishwar-E Hasin, Elizabeth A Nowadnick, Leixin Miao, Fei-Ting Huang, Parivash Moradifar, Debangshu Mukherjee, Ke Wang, Sang-Wook Cheong, Nasim Alem The n=2 Ruddlesden-Popper Ca3Mn2O7 exhibits several unusual properties including negative uniaxial thermal expansion and a complex domain structure and phase transition sequence. These properties can be tied to a polar/non-polar phase coexistence, however little is known about the atomic-scale structure of the phase coexistence or the underlying mechanism driving its formation. We combine electron microscopy measurements with density functional theory (DFT) calculations to directly image and understand the origin of coexisting polar and non-polar phases in Ca2.9Sr0.1Mn2O7 single crystals. At room temperature, we find that the atomic-scale structure of Ca2.9Sr0.1Mn2O7 consists of polar nano-phase regions of A21am symmetry embedded in a non-polar Acaa-symmetry matrix. Combining measurements of the local chemical environment with DFT calculations, we find that the polar nano-phase regions are stabilized by the substitution of Mn2+ dopants for some Ca2+ cations. Our calculations also show that it is energetically favorable for the Mn2+ dopants to cluster in a single rocksalt layer. These results provide insight into strategies to manipulate polar/non-polar phase coexistence and its associated properties. |
Friday, March 18, 2022 9:36AM - 9:48AM |
Y70.00007: First principles study of spin spirals in the multiferroic BiFeO3 Sebastian Meyer, Laurent Bellaiche, Bin Xu, Bertrand Dupé, Matthieu J Verstraete We carry out density functional theory (DFT) calculations to explore the antiferromagnetic (AFM) spin spiral in multiferroic BiFeO3. We calculate the spin spiral energy dispersion E(q) along the high symmetry directions of the pseudo-cubic unit cell, for four different structural phases: cubic, R-3c, R3m and R3c. In all cases, we find a large exchange frustration. The comparison provides detailed insight into how polarization and octahedral anti-phase tilting affect the different magnetic interactions and the magnetic ground state in BiFeO3. For the R3c structural ground state, we find an AFM spin spiral ground state with a periodicity of ∽80 nm in good agreement with experiments and previous findings. This spin spiral is driven by a Dzyaloshinskii-Moriya interaction stemming from the Fe–Bi ferroelectric displacement. The spiral appears to be stable because the anisotropy energy in R3c BiFeO3 is too small to enforce the collinear order. For all the four phases, we discuss the magnetic ground state and identify its stabilization mechanisms. |
Friday, March 18, 2022 9:48AM - 10:00AM Withdrawn |
Y70.00008: Atomic and Electronic Structure Related to Polarization Domains in Hexagonal ABO3 Sizhan Liu, Kai Du, Xiaochen Fang, Sang-Wook Cheong, Jerzy T Sadowski, Trevor A Tyson Oxide ABO3 systems, such as the hexagonal manganites, exhibit complex polarization domain structures. Underlying these domains are unique atomic configurations that determine the polarization. We are examining the atomic-level structure utilizing electron and photon probes to determine how local structure and surface potential variations are connected to the observed polarization. Sub-micron 2D mapping with depth sensitivity is used to connect the polarization with variations in electronic and atomic structure. |
Friday, March 18, 2022 10:00AM - 10:12AM |
Y70.00009: Quantum fluctuation of ferroelectric order in polar metals Fangyuan Gu Polar metallic phase, a metallic phase with long-range ferroelectric (FE) order, has been widely observed in FE materials since the last decade. While it is less conventional, FE order as a spontaneous inversion symmetry breaking actually does not require a global FE polarization that can be effectively screened by merely a couple of percents of metallic carriers. Strangely, FE order is found to be strongly suppressed by metallic carriers and completely destroyed at moderate ~12% carrier density. Here, we propose a general mechanism, carrier-induced quantum fluctuation, to explain this effective destruction of FE order in polar metals. In essence, owing to the virtual kinetic effect of quantum particles, carriers are always dressed by polarizable medium to form larger polarons. Since the local FE correlation inside the polaron is disrupted, the long-range FE order can thus be destroyed when the size of polarons breach the percolation threshold. We demonstrate such polaron formation and its size growth via kinetic strength with a simple model using exact diagonalization, perturbation and quantum Monte Carlo approaches. This proposed quantum mechanism not only provides an intuitive picture for many experimental findings, but also advocates the importance of quantum physics in polar metals, which enables new possibilities in designing FE-based electronic devices. |
Friday, March 18, 2022 10:12AM - 10:24AM |
Y70.00010: "Domain-wall-induced electromagnons in magnetoelectric materials". S. Omid Sayedaghaee, Charles Paillard, Sergey Prosandeev1, Bin Xu, Sergei Prokhorenko, Yousra Nahas, Laurent Bellaiche Amongst the properties of multiferroic materials, magnetoelectric coupling, which provides a handle for controlling electrical dipole moments by applying magnetic fields (or magnetic moments by electric fields), is promising for the design of novel sensors and data storage media with lower power consumption and higher efficiency. In addition, the potential provided by the existence of electromagnons together with the topological defects such as domain walls opens the opportunity of enhancing the magnetoelectric response as well as creating electrically-driven configurable magnonic circuits. In this work, the observation of dynamical couplings between magnons and optical phonons in systems possessing ferroelectric domains is reported which leads to emergence of new hybrid quasi-particles, namely domain-wall-induced electromagnons and induces THz resonances in magnetoelectric responses. Such quasi-particles are preferentially localized either near the domain walls or near the middle of domains due to scatterings. As a result, larger magnetoelectric conversion is acquired that can be exploited to design more reliable and ultrafast magnetoelectric devices with less energy consumption. |
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