Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session F41: Focus Session: BiFeO3 |
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Sponsoring Units: DMP DCOMP Chair: Neil Mathur, University of Cambridge Room: Mile High Ballroom 3C |
Tuesday, March 4, 2014 8:00AM - 8:12AM |
F41.00001: First-principles-derived spin models for the electric control of magnetism in BiFeO$_{3}$ Jun Hee Lee, Randy Fishman While various spin models excellently describe long-range spin spiral states in complex materials, they do not capture atomistic behavior with respect to external perturbations such as electric field or strain. On the other hand, while first-principles approaches capture the atomistic behavior, they cannot practically deal with large systems with long-range spin ordering. In this talk, we demonstrate how spin models and first principles can be synergetically combined to understand the response of complex spin systems with respect to electric field or strain. We present first-principles-derived spin models that show excellent agreement with experimental spin-wave excitations driven by electric field or strain in BiFeO$_{3}$. With the atomistic model, we will discuss how to effectively control magnetism in BiFeO$_{3}$ with the combination of electric field and strain. [Preview Abstract] |
Tuesday, March 4, 2014 8:12AM - 8:24AM |
F41.00002: Magnetoelectric Control of Exchange Coupling in Monodomain BiFeO$_{3}$ Heterostructures Julian Irwin, W. Saenrang, B. Davidson, S. Ryu, S.-B. Baek, C.B. Eom, M.S. Rzchowski, J. Freeland The electric field control of magnetization via the exchange bias coupling of a ferromagnetic and antiferromagnetic orderings has exciting applications in spintronic devices such as magnetic tunnel junctions. We investigate the exchange coupling between the monodomain multiferroic BiFeO$_{3}$(BFO) thin film [1] and a ferromagnetic Co layer. Recently, X-ray magnetic circular dichromism (XMCD) has been used to observe a $\sim$20$^{\circ}$ rotation in the magnetization of the Co when the electric polarization of the BFO is reversed [2]. Due to the formation of an antiferromagnetic surface ``dead layer'' at high temperatures, observed using X-ray linear magnetic dichromism, this rotation is only seen at temperatures below $\sim$150K. Here we investigate the exchange coupling using anisotropic magnetoresistance (AMR) measurements that detect changes in the magnetization of the Co layer. Out approach using AMR can be applied more generally to study exchange coupling in multiferroic systems.\\[4pt] [1] S.H. Baek et al., ``Ferroelastic Switching for Nanoscale Nonvolatile Magnetoelectric Devices'' Nature Materials, 9, 309 (2010).\\[0pt] [2] W. Saenrang et al, ``Magnetoelectric Control of Exchange Coupling in Monodomain BiFeO$_{3}$ Heterostructures,'' in preparation [Preview Abstract] |
Tuesday, March 4, 2014 8:24AM - 8:36AM |
F41.00003: Large room temperature ferroelectric polarization in thin films of solid solution of bismuth ferrite and lead titanate Rajesh Katoch, Rajeev Gupta, Ashish Garg BiFeO$_{3}$ and PbTiO$_{3}$ form a solid solution i.e. (1-x)BiFeO$_{3}$-xPbTiO$_{3}$ showing a morphotropic phase boundary (MPB) at x $=$ 0.30 with high Curie temperature (T$_{\mathrm{c}}$ $\sim$ 630 $^{\circ}$C).Here we present the results of our investigations on the structure and properties of thin films grown by pulsed laser deposition and chemical solution deposition method on Pt/Si substrates and show that the use of PbTiO$_{3}$ buffer layer leads to improvement in the room temperature (RT) ferroelectric response. X ray diffraction and Raman spectroscopy reveal structure to be tetragonal (\textit{P4mm}) at x $=$ 0.35, rhombohedral (\textit{R3c}) at x $=$ 0.25 and two phase (\textit{R3c}$+$\textit{P4mm)} at x $=$ 0.30 exhibiting giant tetragonality (c/a$=$1.17) in bulk. However, PLD grown films remain tetragonal (\textit{P4mm}) for all compositions with P$_{\mathrm{r}}=$40 microcoulombs/cm$^{2}$ while solution grown films showed the structure to be monoclinic (\textit{Cm})at x$=$0.25 and a coexistence of \textit{Cm} and \textit{P4mm} phases for x$=$0.30 and x$=$0.35 with c/a$=$1.02 resulting in large polarization with P$_{\mathrm{r}}=$80microcoulombs/cm$^{2}$ and E$_{\mathrm{c}}=$130 kV/cm. [Preview Abstract] |
Tuesday, March 4, 2014 8:36AM - 8:48AM |
F41.00004: Magnetic coupling in Epitaxial BiFeO$_{3}$-La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ Heterostructures Integrated on Si(100) Srinivasa Rao Singamaneni, J.T. Prater, Fan Wu, C.T. Shelton, J.-P. Maria, J. Narayan We present and discuss the magnetic characteristic of BiFeO$_{3}$ (BFO)/La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) heterostructure, integrated on Si (100) using pulsed laser deposition (PLD) via the domain matching epitaxy (DME) paradigm. The magnetic behavior of this heterostructure, in which a d$^{5}$ system (Fe$^{3+})$ manifested in FE-AFM BFO is epitaxially conjoined at the interface to a multivalent transition metal ion such as Mn$^{3+}$/Mn$^{4+}$ in LSMO exhibits interesting magneto electric coupling phenomenon. The temperature- and magnetic field-dependent magnetization measurements reveal an unexpected enhancement in magnetization and improved magnetic hysteresis squareness originating from the BFO/LSMO interface. We observe a stronger temperature dependence of exchange coupling when the polarity of field cooling is negative as compared to positive field cooling. We believe such an enhancement in magnetization and magnetic coupling is likely directly related to an electronic orbital reconstruction at the interface and complex interplay between orbital and spin degrees of freedom.\\[4pt] [1] S. S. Rao \textit{et al}, Nano Letters, http://dx.doi.org/10.1021/nl4023435. [Preview Abstract] |
Tuesday, March 4, 2014 8:48AM - 9:00AM |
F41.00005: Electro-photo double modulation on the resistive switching behavior and switchable photoelectric effect in BiFeO films Kuijuan Jin, Le Wang We present an electro-photo double modulation on the resistive switching behavior, combining the electro-resistance effect and the photo-resistance effect. The pulse voltages can lead to nonvolatile resistance variations in the Au/BiFeO3/La0.7Sr0.3Mno3 structure, and the laser illumination can also modulate the high and low resistance states. Consequently, four stable resistance states are achieved. Furthermore, we report a switchable photoelectric effect, in which a photocurrent can be created under illumination of the ultraviolet laser, and the direction of the photocurrent depends on the ferroelectric polarization. The present results should have potential applications to develop multi-state memory devices based on perovskite oxides. [Preview Abstract] |
Tuesday, March 4, 2014 9:00AM - 9:12AM |
F41.00006: X-Ray Imaging and Multiferroic Coupling of Cycloidal Magnetic Domains in Ferroelectric Monodomain BiFeO$_3$ P.G. Radaelli, R.D. Johnson, A. Bombardi, Y.-S. Oh, S.-W. Cheong, L.C. Chapon BiFeO$_3$ is perhaps the most studied material among the multiferroics. It is both magnetic and strongly ferroelectric at room temperature, making it potentially suitable for applications. Understanding the interplay between ferroelectric and magnetic domains is, however, essential to control device functionality. In BiFeO$_3$, the Dzyaloshinsky- Moriya interaction promotes the formation of cycloidal magnetic domains with magnetic polarity \emph{co-aligned} with the electrical polarization. We have imaged these magnetic domains at the surface of a ferroelectric monodomain BiFeO$_3$ single crystal by hard x-ray magnetic scattering. Domains up to several hundred microns in size have been observed, corresponding to cycloidal modulations along the wave vector ${\bf k}=(\delta, \delta, 0)$ and symmetry equivalent directions. The rotation direction of the magnetization in all magnetic domains, determined by diffraction of circularly polarized light, was found to be unique and in agreement with first-principle calculations. Imaging of the surface shows that the largest adjacent domains display a 120$^{\circ}$ vortex structure. [Preview Abstract] |
Tuesday, March 4, 2014 9:12AM - 9:24AM |
F41.00007: Modulating the ratio of tetragonal/rhombohedral phases in strained BiFeO$_3$ films by varying the oxygen pressure during deposition Margo Staruch, Heungsoo Kim Room-temperature multiferroic BiFeO$_3$ (BFO) has been the subject of recent research interest due to its potential applications in random access memory and other spintronic devices. Compressive strain in the BFO lattice results in a symmetry change from a rhombohedral to a monoclinically-distorted tetragonal structure, with intermediate strains lying near a morphotropic phase boundary. This has been demonstrated to lead to enhanced piezoelectric and dielectric properties. However, the effect of growth conditions, such as substrate temperature and oxygen partial pressure during deposition, on the multiferroic properties of strained BFO films has yet to be systematically studied. In this work, BiFeO$_3$ thin films were grown on (001) LaAlO$_3$ single crystal substrates by pulsed laser deposition at different oxygen partial pressures. By examining the structure and microstructure of the resulting films, the ratio of the tetragonal-like and rhombohedral phases was found to vary with oxygen deposition pressure. The effects of this modulation on the magnetic and ferroelectric properties will be presented. [Preview Abstract] |
Tuesday, March 4, 2014 9:24AM - 9:36AM |
F41.00008: Symmetry of Highly-Strained BiFeO$_3$ Films in the Ultrathin Regime Yongsoo Yang, Nancy Senabulya, Roy Clarke, Christian M. Schlep\"utz, Christianne Beekman, Wolter Siemons, Hans M. Christen At room temperature, highly-strained BiFeO$_3$ (BFO) films grown on LaAlO$_3$ substrates exhibit a monoclinic structure with a giant c/a ratio ($\sim$1.3) when the films are thicker than 4 nm. Their structural symmetry can be controlled by adjusting the temperature [Appl. Phys. Express {\bf 4}, 095801 (2011), Adv. Mater. {\bf 25}, 5561 (2013)], with a high-temperature tetragonal phase being observed. We report that a structural phase transition can also be achieved by controlling the film thickness: synchrotron x-ray diffraction data shows that the Bragg peak splitting associated with the monoclinic phase disappears as the film thickness decreases below 3 nm, indicating a tetragonal symmetry, but still maintaining the giant c/a ratio. Unlike a similar transition reported for moderately strained BFO grown on SrTiO$_3$ [APL Mater. {\bf 1}, 052102 (2013)], the half-order Bragg peaks indicate that this transition does not involve a significant change in the octahedral tilt pattern of the film. This suggests that the structural evolution of highly-strained BFO films should be understood in terms of the unique (non-octahedral) oxygen coordination of the Fe ion in this highly-strained BFO, not the corner-connectivity of the oxygen octahedra between the film and the substrate. [Preview Abstract] |
Tuesday, March 4, 2014 9:36AM - 9:48AM |
F41.00009: Neutron Scattering Study on Low Energy Phonons in BiFeO$_3$ Guangyong Xu, Zhijun Xu, Jinsheng Wen, Peter Gehring, Stephen Shapiro, Masaaki Matsuda, Toshimitsu Ito, Robert Birgeneau, Barry Winn, Genda Gu We have performed neutron scattering studies on low energy phonon modes in the multiferroic BiFeO$_3$. We show measurements near (100), (110), (200) Bragg peaks on the TA, LA and lowest energy TO modes in a broad temperature range from 300 K to 700 K. The intensities, dispersion, and life times (inversed energy width) of these phonon modes are plotted vs. temperature, and anomalies related to the AFM order (Neel temperature of 640 K) are discussed. We also will also discuss additional low energy modes observed that may be related to the ``electro-magnon'' excitations in this material. This work is supported by the Office of Basic Energy Sciences, DOE. [Preview Abstract] |
Tuesday, March 4, 2014 9:48AM - 10:24AM |
F41.00010: Electric-field control of magnetic order above room temperature Invited Speaker: Manuel Bibes Controlling magnetism by electric fields is a key issue for the future development of low-power spintronics. Progress has been made in the electrical control of magnetic anisotropy, domain structure, spin polarization or critical temperatures. However, the ability to turn on and off robust ferromagnetism at room temperature and above has remained elusive. Here we will present a new approach for the electrical control of magnetic and spintronic properties based on the combination of ferroelectric materials with magnetic transition-metal alloys. We demonstrate a giant, low-voltage control of magnetism, just above room temperature. The data are interpreted in the light of first-principles in terms of both strain and field-effect. Our results correspond to a magnetoelectric coupling larger than previous reports by at least one order of magnitude and open new perspectives for the use of ferroelectrics in spintronics.\\[4pt] Work done in collaboration with Ryan Cherifi, Viktoria Ivanovskaya, Lee Phillips, Unite Mixte de Physique CNRS/Thales; Alberto Zobelli, Laboratoire de Physique des Solides; Ingrid Infante, Ecole Centrale Paris; Eric Jacquet, Stephane Fusil, Unite Mixte de Physique CNRS/Thales; Patrick Briddon, University of Newcastle; Ahmet Unal, Helmholtz Zentrum Berlin; Alexandra Mougin, Laboratoire de Physique des Solides; Sergio Valencia, Helmholtz Zentrum Berlin; Florian Kronast, Laboratoire de Physique des Solides; Brahim Dkhil, Ecole Centrale Paris; and Vincent Garcia, Agnes Barthelemy, Unite Mixte de Physique CNRS/Thales. [Preview Abstract] |
Tuesday, March 4, 2014 10:24AM - 10:36AM |
F41.00011: The interplay of Dzyaloshinskii-Moriya interaction and single-ion anisotropy in multiferroic BiFeO$_{3}$ Jaehong Jeong, P. Bourges, S. Petit, S. Furukawa, M.D. Le, S.-A. Kim, S. Lee, S.-W. Cheong, Je-Geun Park Multiferroic compounds are promising materials for new spintronic devices utilising the coupling between magnetism and ferroelectricity. Among them, BiFeO$_{3}$ is the only example that has both magnetic and ferroelectric transitions above room temperature. It also has the cycloid spin structure with an extremely long period. In order to understand the microscopic magnetic interactions, several inelastic neutron scattering (INS) experiments were carried out using co-aligned single crystals. We could, for the first time, measure the magnon dispersion over the full Brillouin zone and determine the interaction parameters in a Hamiltonian with two Heisenberg interactions between the nearest and the next nearest neighbors. For the further study on the detailed magnetic excitations at low energy, we performed two INS experiments using the triple-axis spectrometer 4F2 at LLB. We also calculated the magnon dispersion using the Hamiltonian that includes Dzyaloshinskii-Moriya (DM) interaction and single-ion anisotropy (SIA), which are associated with the distortion of Fe$^{3+}$ ion in the FeO$_{6}$ octahedra, allowing us to understand the unusual low-energy excitations in BiFeO$_{3}$ by examining the interplay of the DM interaction and SIA. [Preview Abstract] |
Tuesday, March 4, 2014 10:36AM - 10:48AM |
F41.00012: Unified model for spin order induced polarization in multiferroics Hongjun Xiang The microscopic origins of ferroelectricity in different multiferroic systems were theoretically investigated. We proposed a unified model [1,2] which includes purely electronic and ion-displacement contribution simultaneously to describe spin-order induced ferroelectricity. An efficient method [3] was developed to compute the model parameters from first-principles. On the basis of the unified model and density functional calculations, we explained the ferroelectricity induced by the proper-screw spin spiral [2], discovered a novel magnetoelectric coupling mechanism in which the magnitude of the polarization is governed by the exchange striction with the direction by the spin chirality [4], proposed that the ferroelectricity in the chiral-lattice magnet Cu2OSeO3 is due to the unusual single-spin site term [5], unraveled that the magnetoelectric effect observed in BiFeO3 originates from the exchange striction [2].\\[4pt] [1] H. J. Xiang \textit{et al.}, Phys. Rev. Lett. 107, 157202 (2011).\\[0pt] [2] H. J. Xiang \textit{et al.}, Phys. Rev. B 88, 054404 (2013).\\[0pt] [3] H. J. Xiang \textit{et al.}, Phys. Rev. B 84, 224429 (2011).\\[0pt] [4] X. Z. Lu, M.-H. Whangbo, S. Dong, X. G. Gong, and H. J. Xiang, Phys. Rev. Lett. 108, 187204 (2012).\\[0pt] [5] J. H. Yang, Z. L. Li, X. Z. Lu, M.-H. Whangbo, S.-H. Wei, X. G. Gong, and H. J. Xiang, Phys. Rev. Lett. 109, 107203 (2012). [Preview Abstract] |
Tuesday, March 4, 2014 10:48AM - 11:00AM |
F41.00013: Atomic-Scale Electronic Spectra across BiFeO$_{3}$/La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ Complex Oxide Heterointerfaces Ya-Ping Chiu, Bo-Chao Huang, Pu Yu, Ramamoorthy Ramesh, Ying-Hao Chu Atomic-scale evolution of electronic structures across BiFeO$_{3}$/La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ complex oxide heterointerfaces has been revealed using cross-sectional scanning tunneling microscopy and spectroscopy. Analysis of scanning tunneling spectroscopy results exploits the interfacial valence mismatch to influence the electrostatic configurations across the BiFeO$_{3}$/La$_{0.7}$Sr$_{0.3}$MnO$_{0.3}$ heterointerfaces. Spatially unit-cell-by-unit-cell resolved electronic states at the atomic level reveal how the control of material interfaces at the atomic level to determine the ferroelectric polarization in BiFeO$_{3}$. [Preview Abstract] |
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