Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P37a: Dielectric and Ferroelectric Oxides VFocus
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Sponsoring Units: DMP Chair: Sang Cheong, Rutgers University Room: 383 |
Wednesday, March 15, 2017 2:30PM - 3:06PM |
P37a.00001: Photostriction in ferroelectric and multiferroic materials from first principles Invited Speaker: Charles Paillard The so-called Bulk Photovoltaic Effect (BPVE), occurring in materialslacking inversion symmetry, has attracted interest for the design of new solar cells. Hence, non-centrosymmetry of ferroelectrics makes themnatural candidates to the design of suchsolar cells. Itis also fundamental to their piezoelectric properties, $i.e.$the coupling of their electric polarization to strain. Therefore, ferroelectrics offer a natural route towards the realization of light-induced actuators among the class of photostrictive materials. Experimental evidences towards this goal have appeared, with intense studies of the photostriction in bismuth ferrite, in which both thesteady state response andthe transientgiant shear strain induced by femtoseconds laser pulses wereattributed to the conjunction of the BPVE and the piezoelectric effect. However, theory has not investigated the coupling of light with electromechanical properties of ferroelectrics on a microscopic scale. To tackle this problem, we employ a $\Delta $-SCF scheme in which the occupation numbers of the Kohn-Sham orbitals are constrained. We apply this method to various prototypical ferroelectric and multiferroic materials, such as bismuth ferrite. This scheme yields a photostrictioneffect of the same order of magnitude than the ones recently observed. It also predicts a strong dependence of photostrictive response on both the reached conduction state and the crystallographic direction (along which this effect is determined). In particular, according to our results, BFO should shrink along its pseudo-cubic and polarization axes, with the pseudo-cubic angle getting closer to 90\textdegree , while the directions perpendicular to the polarization, such as [110]$_{pc}$, stretches under excitation of electrons in the conduction band. Another of our main results is that photostriction is found to originate from the combination of screening of the polarization at the unit cell scale by the photoexcited carriers, and converse piezoelectric effect. [Preview Abstract] |
Wednesday, March 15, 2017 3:06PM - 3:18PM |
P37a.00002: Tailoring the properties of 3d transition metal perovskite oxides through strain: a first-principles study Oswaldo Di\'eguez, Jorge \'I\~niguez In this talk I will present our recent computational work on how strain can stabilize phases that are higher-energy local minima of the bulk material of 3d transition metal perovskite oxides. Particular examples will include BiMnO$_3$, that is a ferromagnet paraelectric in bulk, but we predict that it is a paramagnet ferroelectric as an epitaxial film, and Bi$_2$NiMnO$_6$, which we predict that is a ferroelectric ferromagnet when grown under epitaxial tension. We will also compare the behavior in bismuth transition-metal oxides with that in other perovskites such as BaTiO$_3$ and PbTiO$_3$. [Preview Abstract] |
Wednesday, March 15, 2017 3:18PM - 3:30PM |
P37a.00003: Inner structure of topological defects in hexagonal manganites Konstantin Shapovalov, Megan Holtz, Julia Mundy, David Muller, Zewu Yan, Edith Bourret-Courchesne, Dennis Meier, Andres Cano The diverse opportunities inspired by the properties of topological defects in solid-state systems have triggered the broad interest in this rapidly evolving field. Particularly promising are topological defects in electrically and magnetically ordered materials -- robust nanoscale objects that can readily be controlled by external fields, opening innovative pathways in active nanoelectronics and related areas. Hexagonal manganites (RMnO$_3$, R = Sc, Y, In, Dy -- Lu) host an explicitly large variety of topological defects, including neutral and charged domain walls, multiferroic vortices, thus providing new fertile ground for the investigation of topology-related phenomena. Despite the growing interest, very little is known about the inner structure and local symmetry of the topological defects in RMnO$_3$. In this work, we quantify the vortices and domain walls emerging in these systems combining the scanning transmission electron microscopy and Landau-theory-based analytical calculations. Thus we observe and reproduce key novel features of the topological defects such as the emergence of a continuous U(1) symmetry at the vortex cores, and link these features to fundamental properties characterizing the material such as the correlation lengths. [Preview Abstract] |
Wednesday, March 15, 2017 3:30PM - 3:42PM |
P37a.00004: Optical Investigation on the Effect of Vortex Domains on Electronic Transitions in HoMnO3 Single Crystals T. D. Kang, Nara Lee, H. Y. Choi, Y. J. Choi, S. C. Chae We investigated on the effect of vortex domain on the electronic transitions of HoMnO3 using optical spectroscopy. We observed different characteristics for d-d and p-d electronic transitions, which are centered near 1.7 eV and 5 eV at room temperature, respectively. The band edge energy of the p-d transition with vortex domains appears to show a clear increase which is attributed to the reduced hybridization between O p and Mn d states, while characteristics of the d-d transition does have distinct difference between vortex and normal states. However, from temperature dependent measurement, on the contrary, we observed the peak position of the d-d transition varying significantly with temperature between 10K to 300K, while the edge energy of the p-d transition is almost invariable. Such huge shifts of the d-d transition peak energy with temperature is known due to the antiferromagnetic superexchange interaction between nearest-neighbor Mn ions separated by oxygens. [Preview Abstract] |
Wednesday, March 15, 2017 3:42PM - 3:54PM |
P37a.00005: Effect of Electromechanical Properties in Mn-doped BaTiO$_3$ Hiroyuki Takenaka, R.E. Cohen Experimental studies reported that Mn doping in BaTiO$_3$ could improve their electromechanical properties. In addition, ageing process gives rise to a significant reversible strain effect. Performing density functional theory (DFT) calculations, we find that Mn dopant with oxygen vacancy induces local electric field of 20 MV/m in 2x2x2 (39 atom) supercell. In order to understand effects of the electromechanical properties from phenomenological point of view, we optimize electric enthalpies in Landau-Devonshire model, parametrized from DFT results, under applying electric fields. We show dielectric constant and piezoelectric coefficients from the optimized polarization paths. [Preview Abstract] |
Wednesday, March 15, 2017 3:54PM - 4:06PM |
P37a.00006: Mn$_{1-x}$Co$_x$WO$_4$: From x = 0.05 to x = 0.17- a study of the multiferroic state under high pressure Melissa Gooch, Narayan Poudel, Bernd Lorenz, Kao-Chen Liang, Yaqi Wang, Y. Y. Sun, Jinchen Wang, Feng Ye, Jaime Fernandez-Baca, Ching-Wu Chu It is well understood for multiferroic materials that small perturbations from chemical substitution, magnetic and electric fields, or external pressure can result in new states with different magnetic orders and ferroelectric properties. One such system is Mn$_{1-x}$Co$_x$WO$_4$, which has an interesting and complex phase diagrams where two multiferroic phase coexist at x = 0.15. At this boundary on the phase diagram the conical spin extends to lower temperature, in addition to the a-c spiral spin structure forming below 7 K. On either side of the boundary we have a spiral spin structure for x $<$ 0.15 and a conical spin for x $>$ 0.15. To gain further insight into this system, high pressure polarization and dielectric measurements up to 18 kbars, as well as high pressure neutron experiments were conducted. The effect of external pressure on the Mn$_{1-x}$Co$_x$WO$_4$ system can be described as similar to Co doping. Suggesting we have a polarization flop, where the a-c spiral is stabilized into the conical spin leading to the increased polarization that is observed for the x = 0.135. [Preview Abstract] |
Wednesday, March 15, 2017 4:06PM - 4:18PM |
P37a.00007: Prediction of new ferroelectrics and multiferroics Hongjun Xiang Ferroelectrics, whose spontaneous electric polarization can be switched electrically, are useful for a range of applications, such as memory or sensing devices. However, relatively few naturally occurring materials are ferroelectric. Available theoretical methods for designing new ferroelectrics are usually restricted to high symmetric systems. We have developed a more general computational approach that can be applied to any system, and have used it to identify previously unrecognised classes of ferroelectrics [1]. With this approach, we show that the R-3c perovskite structure can become ferroelectric by substituting half of the B-site cations. ZnSrO$_{\mathrm{2}}$ with a non-perovskite layered structure can also be ferroelectric through the anion substitution. Moreover, our approach can be used to design new multiferroics as illustrated in the case of fluorine substituted LaMnO$_{\mathrm{3}}$. In addition, we predict that two-dimensional P$_{\mathrm{2}}$O$_{\mathrm{3}}$ adopt two possible stable ferroelectric structures (P$_{\mathrm{2}}$O$_{\mathrm{3}}$-I and P$_{\mathrm{2}}$O$_{\mathrm{3}}$-II) as the lowest energy configurations within a given layer thickness. Their electric polarizations are perpendicular and parallel to the lateral plane, respectively. We propose that P$_{\mathrm{2}}$O$_{\mathrm{3}}$ could be used in a novel nanoscale multiple-state memory device [2]. References: 1. Ke Xu, Xue-Zeng Lu, and H. J. Xiang, arXiv:1602.07439 (2016) (To be published in npj Quantum Materials). 2. Wei Luo and H. J. Xiang, Angew. Chem. Int. Ed \textbf{55}, 8575 (2016). [Preview Abstract] |
Wednesday, March 15, 2017 4:18PM - 4:30PM |
P37a.00008: Investigating Magnetism in the Multiferroic RA$_{\mathrm{3}}$(BO$_{\mathrm{3}})_{\mathrm{4}}$ System at Low Temperature T. Yu, H. Zhang, L. N. Bezmaternykh, K. Page, Y.-S. Chen, T. A. Tyson The Multiferroic system HoAl$_{\mathrm{3}}$BO$_{\mathrm{3}})_{\mathrm{4}}$ is known to exhibit a strong coupling of magnetic field to the electrical polarization at low temperature. The nature of magnetic order and Ho site at low temperature is not known. However measurements reveal magnetic ordering in Ho site in HoFe$_{\mathrm{3}}$(BO$_{\mathrm{3}})_{\mathrm{4}}$ at low temperature. Our previous work revealed enhanced correlation between neighboring HoO$_{\mathrm{6}}$ polyhedra for magnetic fields up to 3 T. In this work, we further investigate the origin of the magnetoelectric effect of the RA$_{\mathrm{3}}$(BO$_{\mathrm{3}})_{\mathrm{4}}$ system by neutron scattering and structural optimization with DFT calculation. This work is supported by DOE Grant DE-FG02-07ER46402. [Preview Abstract] |
Wednesday, March 15, 2017 4:30PM - 4:42PM |
P37a.00009: Theoretical study of domain wall dynamics in multiferroic hexagonal manganites Urko Petralanda, Sergey Artyukhin, Xiaoyu Wu, Sang-Wook Cheong, Keji Lai Multiferroic hexagonal manganites are antiferromagnetic improper ferroelectrics where unit-cell-tripling buckling of oxygen bipyramids induces polarization and, in some compounds, weak ferromagnetism. Understanding the dynamical effects controlling motion of clamped structural, ferroelectric and magnetic domain walls (DW) in these materials is critical to design devices based on controlled switching of DWs. However, the study of DW dynamics in realistic multiferroics has been mainly focused on proper ferroelectrics and ferromagnetic materials so far, and for multiferroics was mostly limited to estimating switching barriers [1,2]. We develop a model Hamiltonian to describe the driven dynamics of DWs in hexagonal manganites, with parameters extracted from ab-initio calculations. \newline \newline [1] Yu Kumagai, N. A. Spaldin Nature Communications 4, 1540 (2012) \newline \newline [2] N. A. Benedek and C. J. Fennie, Phys. Rev. Lett. 106, 107204 (2011) [Preview Abstract] |
Wednesday, March 15, 2017 4:42PM - 4:54PM |
P37a.00010: Interstitial oxygen as a source of p-type conductivity in RMnO$_{\mathrm{3\thinspace }}$hexagonal manganites Sandra Helen Skjærvø, Espen T. Wefring, Silje K. Nesdal, Nikolai H. Gaukås, Gerhard H. Olsen, Julia Glaum, Thomas Tybell, Sverre M. Selbach We use a combination of experiments and first principles electronic structure calculations to elucidate the effect of interstitial oxygen anions, O$_{\mathrm{i}}$, on the electrical and structural properties of h-YMnO$_{\mathrm{3}}$. Hexagonal manganites, h-$R$MnO$_{\mathrm{3}}$ ($R =$ Sc, Y, Ho-Lu) have been intensively studied for their multiferroic properties, magnetoelectric coupling, topological defects and electrically conducting domain walls. Although point defects strongly affect the conductivity of transition metal oxides, the defect chemistry of h-$R$MnO$_{\mathrm{3}}$ has received little attention. Enthalpy stabilized interstitial oxygen anions are shown to be the main source of $p$-type electronic conductivity, without reducing the spontaneous ferroelectric polarization. A low energy barrier interstitialcy mechanism is inferred from Density Functional Theory calculations to be the microscopic migration path of O$_{\mathrm{i}}$. Since the O$_{\mathrm{i}}$ content governs the concentration of charge carrier holes, controlling the thermal and atmospheric history provides a simple and fully reversible way of tuning the electrical properties of h-$R$MnO$_{\mathrm{3}}$. [Preview Abstract] |
Wednesday, March 15, 2017 4:54PM - 5:06PM |
P37a.00011: Exploration of the Structure of the High Temperature Phase of the Hexagonal RMnO$_{\mathrm{3}}$ System T Wu, T. A. Tyson, H. Zhang, T. Yu, K. Page, S. Ghose Temperature dependent structural studies of the high temperature phase of hexagonal RMnO3 systems have been conducted. Both long range and local structural probes have been utilized. Discussions of the appropriate space groups and local distortions relevant to length scale will be given. Ab initio MD simulations are used to interpret the observations. This work is supported by DOE Grant DE-FG02$-$07ER46402. [Preview Abstract] |
Wednesday, March 15, 2017 5:06PM - 5:18PM |
P37a.00012: Low-energy Structural Dynamics of Multiferroic Domain Walls in Hexagonal Rare-earth Manganites Xiaoyu Wu, Urko Petralanda, Lu Zheng, Yuan Ren, Rongwei Hu, Sang-Wook Cheong, Sergey Artyukhin, Keji Lai Multiferroic domain walls (DWs), the natural interfaces between domains with different order parameters, usually exhibit unconventional functionalities. For instance, recent discovery of the ferroelectric DW conduction highlights its extraordinary electronic structure that is absent in bulk domains. The structural dynamics of individual DWs in the microwave regime, however, have not been fully explored due to the lack of spatially resolved studies. Here, we report the broadband (10$^{\mathrm{6}}$--10$^{\mathrm{10}}$ Hz) scanning impedance microscopy results on the interlocked anti-phase boundaries and ferroelectric DWs in hexagonal rare-earth manganites. Surprisingly, the effective conductivity of the (001) DWs displays a 10$^{\mathrm{6}}$-fold increase from dc to GHz frequencies, while the effect is absent on surfaces with in-plane polarized domains. First-principles and model calculations indicate that the frequency range and selection rules are consistent with the periodic sliding of the DW around its equilibrium position. This DW acoustic-wave-like mode, which is associated with the synchronized oscillation of local polarization and apical oxygen atoms, is localized perpendicular to the DW but free to propagate along the DW plane. Our results break the ground to understand structural DW dynamics and exploit new interfacial phenomena for novel devices. [Preview Abstract] |
Wednesday, March 15, 2017 5:18PM - 5:30PM |
P37a.00013: Vortex Ferroelectric Domains, Large-loop Weak Ferromagnetic Domains, and Their Decoupling in Hexagonal LuFeO3 Kai Du, Bin Gao, Yazhong Wang, Rongwei Hu, Fei-Ting Huang, Sang-Wook Cheong The direct domain coupling of spontaneous ferroelectric polarization and magnetic moment can result in giant magnetoelectric coupling, which is essential to achieve mutual controls and real applications of multiferroics. Recently, the possible bulk domain coupling of ferroelectricity(FE) and weak ferromagnetism(WFM) has been theoretically predicted in hexagonal LuFeO3(h-LuFeO3). Thus, it is important to experimentally study the possibility of this effect. Here, we report the successful growth of Sc-stabilized h-LuFeO3 single crystals, as well as the first time visualization of their cloverleaf pattern of vortex FE domains and large-loop WFM domains. FE and WFM domains are distinct regarding the size and shape. There exists no interlocking of FE and WFM domain walls. These demonstrate the decoupling between FE and WFM in h-LuFeO3, which is in contrast to the theoretical prediction. This domain decoupling can be explained as the consequence of the structure-mediated coupling between polarization and in-plane antiferromagnetic spins. Our results indicate the magnetic topological charge tends to be identical with structural topological charge. These discoveries could provide new insights into inducing direct domain coupling between FE and WFM mediated through structural distortion. [Preview Abstract] |
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