Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session L37a: Dielectric and Ferroelectric Oxides IVFocus
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Sponsoring Units: DMP Chair: Tomas Zac Ward, Oak Ridge National Laboratory Room: 383 |
Wednesday, March 15, 2017 11:15AM - 11:51AM |
L37a.00001: Multiferroic phase boundaries and properties of BiFeO$_{\mathrm{3}}$-based solid solutions Invited Speaker: Zuo-Guang Ye The presence of morphotropic phase boundary in ferroelectric solid solutions (FE-MPB) is known to be crucial for high piezoelectricity. Similarly, magnetic MPB (M-MPB) is found in a few ferromagnets and is proved to be greatly beneficial to the magnetostricitive response. One naturally asks if in multiferroics that exhibit both ferroelectricity and (ferro-/antiferro-)magnetism, the FE-MPB and M-MPB could exist simultaneously, and if so, what the relation between these two kinds of MPB would be, and how they would affect the properties. In this paper, we report the studies of ferroelectric and magnetic double morphotropic phase boundaries in BiFeO$_{\mathrm{3}}$-based multiferroics. The effects of dysprosium ion on the structure and local polar domains of the BiFeO$_{\mathrm{3}}$-based systems were investigated firstly in the Dy-substituted solid solutions of 0.66Bi$_{\mathrm{1-}}_{x}$Dy$_{x}$FeO$_{\mathrm{3}}$-0.34PbTiO$_{\mathrm{3}}$. It is found that the substitution of Dy affects the structural symmetry and phase component of the multiferroic solid solution, and thereby enhances its ferroelectric order. A (weak) ferromagnetic state is induced at room temperature for the rhombohedral compositions with $x \quad \ge $ 0.10. The introduction of Dy into 0.66BiFeO$_{\mathrm{3}}$-0.34PbTiO$_{\mathrm{3}}$ leads to the breaking of its antiferromagnetic order below N\'{e}el temperature and thereby the formation of (weak) ferromagnetic ordering at room temperature when the substitution rate exceeds a critical value ($x \quad \ge $ 0.10), making the 0.66Bi$_{\mathrm{1-}}_{x}$Dy$_{x}$FeO$_{\mathrm{3}}$-0.34PbTiO$_{\mathrm{3}}$ system one of rare room-temperature ferromagnetic and ferroelectric materials, i.e. a true multifrroic. A comprehensive ferroelectric-magnetic phase diagram is established in terms of temperature and composition, which depicts the coexistence of a FE-MPB and a FM-MPB. These two kinds of MPBs overlap with each other. Such unusual coincidence of both magnetic MPB and ferroelectric MPB, the so-called double MPB, points to new kinds of couplings among the multiple physical quantities so that such effects as magnetoelectricity, magnetostrictive and piezoelectricity, could be enhanced near the overlapping MPB region. In addition, we find an unusual magnetic pole inversion behavior in mutiferroic (1-x)BiFeO$_{\mathrm{3}}$-xDyFeO$_{\mathrm{3}}$ solid solution, which can be tuned by varying the concentration of the magnetic ion Dy$^{\mathrm{3+}}$ in the solid solution in a wide composition range. [Preview Abstract] |
Wednesday, March 15, 2017 11:51AM - 12:03PM |
L37a.00002: Controlled morphotropic phase transitions by strain doping Andreas Herklotz, Stefania Florina Rus, Er-Jia Guo, Anthony Wong, Nina Balke, Thomas Zac Ward Transitions between rhombohedral and tetragonal phases of ferroelectric oxides are of great interest since the competition of these phases at so called morphotropic phase boundaries (MPB) typically leads to extraordinary physical properties. Utilizing external parameters such as the material’s composition or mechanical pressure has been the standard approach to functionalize these MPBs. Here, we demonstrate that “strain doping” via low-energy He implantation is an alternative, controllable, and highly flexible way to induce morphotropic phase transition in ferroelectric oxide thin films. We show that strain doping of rhombohedral BiFeO$_3$ films leads to a gradual transition to a supertetragonal phase that can be reversibly tuned by controlling the He concentration in the film. The changes in structure are shown to dramatically affect physical properties. We argue that our approach to tailor phase coexistence by strain doping is not limited to BiFeO$_3$ films, but should be widely applicable to ferroelectric thin films with competing morphotropic phases. [Preview Abstract] |
Wednesday, March 15, 2017 12:03PM - 12:15PM |
L37a.00003: Improper electric polarization in perovskite oxides with two magnetic sublattices Jorge Iniguez, Hong Jian Zhao, Xiang Ming Chen, Laurent Bellaiche I will discuss the sources of magnetically-driven ferroelectric order in {\sl AB}O$_{3}$ perovskite oxides with magnetic {\sl A} and {\sl B} cations that order in simple, short-period spin structures. I will focus on the families of rare-earth orthoferrites and orthochromites, which are currently receiving much attention because of their multiferroic and fast spin dynamics properties. Our first-principles calculations reveal that the largest effects correspond to collinear spin configurations and are driven by non-relativistic exchange-strictive mechanisms. Our simulations allow us to determine the dominant magnetostructural couplings underlying the observed improper ferroelectricity, including a striking magnetically-driven piezoelectric effect. Further, I will show it is possible to derive phenomenological and atomistic theories that describe such couplings in a generic perovskite lattice; this allows us to predict how the observed multiferroic effects can be enhanced, and even how similar ones can be obtained in other perovskite families. Our results thus highlight perovskites with two magnetic sublattices as a rich playground for novel magnetoelectric effects. [Nat. Comms. (in press)] [Preview Abstract] |
Wednesday, March 15, 2017 12:15PM - 12:27PM |
L37a.00004: Bismuth Manganite Defect Structure Daniel Pajerowski Bismuth manganite (BMO) has had an interesting recent history. BMO is reported to be ferromagnetic, ferroelectric, and magnetoelectric. However, it is very difficult to stabilize in the highly distorted perovskite structure that hosts the aforementioned properties. Initial reports suggested non-centrosymmetric structure compatible with ferroelectricity, but the current understanding is that stoichiometric BMO is centrosymmetric. Studies on films have historically reported anomalously low magnetic moments compared to the bulk, but polarized neutron reflectometry shows that the magnetization density is very similar to the bulk while the film morphology is actually the complicated feature. X-ray absorption suggests that the orbital order in the films is also similar to the bulk. X-ray spectroscopy and electron microscopy suggest a possible non-stoichiometric phase as the source of multiferroicity in some BMO films grown on Strontium Titanate (STO). Candidates for this the ferroelectric phase will be presented and compared with the data of BMO on STO. [Preview Abstract] |
Wednesday, March 15, 2017 12:27PM - 12:39PM |
L37a.00005: Permanent ferroelectric retention of BiFeO3 mesocrystal Qing He, Ying-Hui Hsieh, Qian Zhan, Chun-Gang Duan, Long-Qing Chen, Ying-Hao Chu Non-volatile electronic devices based on magnetoelectric multiferroics have triggered new possibilities of outperforming conventional devices for applications. However, ferroelectric reliability issues, such as imprint, retention and fatigue, must be solved before the realization of practical devices. In this study, everlasting ferroelectric retention in the heteroepitaxially constrained multiferroic mesocrystal is reported, suggesting a new approach to overcome the failure of ferroelectric retention. Studied by scanning probe microscopy and transmission electron microscopy, and supported via the phase-field simulations, the key to the success of ferroelectric retention is to prevent the crystal from ferroelastic deformation during the relaxation of the spontaneous polarization in a ferroelectric nanocrystal. [Preview Abstract] |
Wednesday, March 15, 2017 12:39PM - 12:51PM |
L37a.00006: Imaging the Dynamics of the Ferroelectric Stripe Phase Near a Field-Driven Phase Transition in Bismuth Ferrite Nouamane Laanait, Qian Li, Zhan Zhang, Sergei Kalinin Electric field-driven phase transitions in multiferroic systems such as Bismuth Ferrite could potentially host interesting domain dynamics due to the coexistence of multiple order parameters. Structural imaging of these dynamics under a host of elastic and electric boundary conditions is therefore of interest. Here, we present X-ray diffraction microscopy (XDM) studies of the domain wall dynamics in a bismuth ferrite thin-film near the field-driven transition from rhombohedral to monoclinic (R to M). XDM is a novel full-field imaging technique that uses Bragg diffraction contrast to image structural configurations with sub-100nm lateral resolutions and fast acquisition times (milliseconds to seconds per image). We find that under electric fields \textasciitilde 100 kV/cm, a bismuth ferrite thin-film (100 nm BiFeO3/DyScO3 (110)) undergoes a structural phase transition but that this new phase (M) is pinned by the preexisting ferroelectric/ferroelastic stripe phase (R). At higher fields (\textasciitilde 300 kV/cm), we observe unusually slow domain wall dynamics in the stripe phase, consisting of periodicity doubling, domain wall roughening and crowding. These observed ferroelastic domain wall spatial dynamics are weakly constrained by the crystal symmetry of the orthorhombic substrate but exhibit nonlinear dynamics more commonly associated with disordered nematic systems. [Preview Abstract] |
Wednesday, March 15, 2017 12:51PM - 1:03PM |
L37a.00007: Magnetic field induced transitions in BiFeO$_3$ M. Matsuda, S. Dissanayake, T. Hong, W. Ratcliff II, Y. Zhao, Z. Xu, S. Miyahara, N. Furukawa, S. Kawachi, A. Miyake, M. Tokunaga Bulk BiFeO$_3$ exhibits a spiral spin structure below 640 K and also a transition to a canted G-type structure in magnetic field. Very recently, a new magnetic phase was found just below the critical field to the canted G-type phase. [1] Neutron diffraction measurements were performed to clarify the magnetic structure in the intermediate phase as well as the magnetic domain redistribution in magnetic field. There are three magnetic domains with different easy planes at ambient magnetic field. We found that with applying field perpendicular to one of the magnetic domains (M1), the other two domains merge to the M1 domain around 5 T. With further applying field, there occurs a first order magnetic transition to the intermediate phase. The incommensurate peaks observed perpendicular to the magnetic field at low fields become commensurate in the intermediate phase. We will discuss the magnetic structure in this phase. [1] S. Kawachi et al., in preparation. This research at ORNL's HFIR was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. [Preview Abstract] |
Wednesday, March 15, 2017 1:03PM - 1:15PM |
L37a.00008: The many local minima in energy surface of bismuth ferrite: a first-principles exploration Akansha Singh, Enric Canadell, Jorge \'{I}\~{n}iguez, Oswaldo Di\'{e}guez Multiferroic bismuth ferrite is one of the most studied materials in the last decade because it is one of the very few that shows polar and magnetic orderings coexisting at room temperature. BiFeO$_3$ displays a variety of phases under different conditions of temperature, pressure, and epitaxial strain. In previous work$^{\dagger}$, we identified these phases as local minima in the energy surface of bulk BiFeO$_3$, and we reported that this multiferroic shows a large amount of other phases as local minima. In the present first-principle study, we used an unbiased search scheme based on an evolutionary algorithm to systematically map the low-energy phases of BiFeO$_3$. We found that the potential energy surface of BiFeO$_3$ is very complex and it has a large number of local minima including non-perovskite structures. In order to assess what makes BiFeO$_3$ different from typical perovskite oxides, where the number of local minima is much smaller, we have also explored the potential energy surface of BaTiO$_3$ and PbTiO$_3$. ${\dagger}~$O. Di\'{e}guez, O. E. Gonz\'{a}lez-V\'{a}zquez, J. C. Wojde\l{}, and J. \'{I}\~{n}iguez, Phys. Rev. B {\bf{83}}, 094105 (2011). [Preview Abstract] |
Wednesday, March 15, 2017 1:15PM - 1:27PM |
L37a.00009: Evolution of structural distortion in BiFeO3 thin films probed by second-harmonic generation Kuijuan Jin, Jiesu Wang, Junxing Gu BiFeO3 thin films have drawn much attention due to its potential applications for novel magnetoelectric devices and fundamental physics in magnetoelectric coupling. However, the structural evolution of BiFeO3 films with thickness remains controversial. Here we use an optical second-harmonic generation technique to explore the phase-related symmetry evolution of BiFeO3 thin films with the variation of thickness. The crystalline structures for 60 and 180-nm-thick BiFeO3 thin films were characterized by high-resolution X-ray diffractometry reciprocal space mapping and the local piezoelectric response for 60-nm-thick BiFeO3 thin films was characterized by piezoresponse force microscopy. The present results show that the symmetry of BiFeO3 thin films with a thickness below 60 nm belongs to the point group 4mm. We conclude that the disappearance of fourfold rotational symmetry in SHG s-out pattern implies for the appearance of R-phase. The fact that the thinner the film is, the closer to 1 the tensor element ratio $\chi $31/$\chi $15 tends, indicates an increase of symmetry with the decrease of thickness for BiFeO3 thin films. email: kjjin@iphy.ac.cn [Preview Abstract] |
Wednesday, March 15, 2017 1:27PM - 1:39PM |
L37a.00010: Size effect on lattice and magnetic excitations in BiFeO3 nanoparticles Ian Aupiais, Maximilien Cazayous Multiferroics are compounds that show ferroelectricity and magnetism. BiFeO3, by far the most studied, has outstanding ferroelectric properties, a cycloidal magnetic order in the bulk, and many unexpected virtues such as conductive domain walls or a low bandgap of interest for photovoltaics. While this flurry of properties make BiFeO3 a paradigmatic multifunctional material, most are related to its ferroelectric character, and its other ferroic property, antiferromagnetism, has not been investigated extensively, especially in nanoparticles. In this talk, we will bring insight into the rich physics of BiFeO3 nanoparticles with various size through Raman scattering and Transmission Electron Microscopy. We will show how the phonon modes, the spin orders and the spin excitations are modified around the critical size of 66 nm, related to the periodicity of the spin cycloid. [Preview Abstract] |
Wednesday, March 15, 2017 1:39PM - 1:51PM |
L37a.00011: Resistive and Ferroelectric-Domain Switching in Multiferroic BiFeO$_{\mathrm{3}}$ Films J.G. Ramirez, I. C. Arango, M. F. Gomez, C. Dominguez, S. Sulekar, A. Cardona, J. Trastoy, J. C. Nino, I. K. Schuller, M. E. Gomez Resistive switching (RS) in oxides has attracted much attention due to its potential application for nonvolatile memory and neuromorphic computing devices. Here we study the voltage-induced RS mechanisms in metal/multiferroic/semiconductor (Au/BiFeO$_{\mathrm{3}}$/Nb:SrTiO$_{\mathrm{3}})$ thin film vertical devices. We found switching with R$_{\mathrm{ON}}$ and R$_{\mathrm{OFF}}$ ratios as big as 0.16 at voltages starting at $\pm$ 2V. Further voltage increase produced an intensification of the RS effects, until dielectric breakdown was reached. Interestingly, the voltage at which the RS effect appears coincides with the coercive voltage of the ferroelectric polarization in similar BiFeO$_{\mathrm{3}}$ films, as measured by piezoelectric force microscopy. This suggests that the primary RS mechanism is the ferroelectric switching. Impedance spectroscopy measurements show filamentary contributions after ferroelectric saturation, possible due to voltage-induced movement of charge defects across the device and therefore suggesting an additional RS mechanism. [Preview Abstract] |
Wednesday, March 15, 2017 1:51PM - 2:03PM |
L37a.00012: Ferroelectric domain states of a T-BiFeO3 thin film investigated by second harmonic generation microscopy Chang Jae Roh, Sun Young Hamh, Chang Su Woo, Kwang Eun Kim, Chan Ho Yang, Jong Seok Lee We investigate a ferroelectric domain state of a multiferroic tetragonal(T)-BiFeO3 thin film by using second harmonic generation (SHG) microscopy. We illuminate the sample with a femtosecond laser with a center wavelength of 800 nm, and monitor the SHG response with full variations of input and output polarizations of light. By scanning the sample with a beam size reduced down to 1 $\mu $m, we could observe clear signatures of nano- and micro-sized domains and their inhomogeneous distributions. Also, we observed a clear signature of temperature-dependent phase transition in the muliferroelectric state which is possibly attributable to the rotation of the polarization axis by 45 degrees [Preview Abstract] |
Wednesday, March 15, 2017 2:03PM - 2:15PM |
L37a.00013: Bulk photovoltaic effect in epitaxial (K, Nb) substituted BiFeO3 thin films Radhe Agarwal, Fan Zheng, yogesh sharma, Seungbum Hong, Andrew Rappe, Ram Katiyar We studied the bulk photovoltaic effect in epitaxial (K, Nb) modified BiFeO3 (BKFNO) thin films using theoretical and experimental methods. Epitaxial BKFNO thin films were grown by pulsed laser deposition (PLD). First, we have performed first principles density function theory (DFT) using DFT$+$U method to calculate electronic band structure, including Hubbard-Ueff (Ueff$=$U-J) correction into Hamiltonian. The electronic band structure calculations showed a direct band gap at 1.9 eV and a defect level at 1.7 eV (in a 40 atom BKFNO supercell), sufficiently lower in comparison to the experimentally observed values. Furthermore, the piezoforce microscopy (PFM) measurements indicated the presence of striped polydomains in BKFNO thin films. Angle-resolved PFM measurements were also performed to find domain orientation and net polarization directions in these films. The experimental studies of photovoltaic effect in BKNFO films showed a short circuit current of 59 micro amp/cm2 and open circuit voltage of 0.78 V. We compared our experimental results with first principles shift current theory calculations of bulk photovoltaic effect (BPVE).The synergy between theory and experimental results provided a realization of significant role of BPVE in order to understand the photovoltaic mechanism in ferroelectrics. [Preview Abstract] |
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