Browsing by Author "Martin, L. W."

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A Strain-Driven Morphotropic Phase Boundary in BiFeO(3)
(2009-11-13)
Zeches, R. J.
;
Rossell, M. D.
;
Zhang, J. X.
;
Hatt, A. J.
;
He, Q.
Piezoelectric materials, which convert mechanical to electrical energy and vice versa, are typically characterized by the intimate coexistence of two phases across a morphotropic phase boundary. Electrically switching one to the other yields large electromechanical coupling coefficients. Driven by global environmental concerns, there is currently a strong push to discover practical lead-free piezoelectrics for device engineering. Using a combination of epitaxial growth techniques in conjunction with theoretical approaches, we show the formation of a morphotropic phase boundary through epitaxial constraint in lead-free piezoelectric bismuth ferrite (BiFeO(3)) films. Electric field-dependent studies show that a tetragonal-like phase can be reversibly converted into a rhombohedral-like phase, accompanied by measurable displacements of the surface, making this new lead-free system of interest for probe-based data storage and actuator applications.
A Strain-Driven Morphotropic Phase Boundary in BiFeO3
(2009-11-13)
Zeches, R. J.
;
Rossell, M. D.
;
Zhang, J. X.
;
Hatt, A. J.
;
He, Q.
Piezoelectric materials, which convert mechanical to electrical energy and vice versa, are typically characterized by the intimate coexistence of two phases across a morphotropic phase boundary. Electrically switching one to the other yields large electromechanical coupling coefficients. Driven by global environmental concerns, there is currently a strong push to discover practical lead-free piezoelectrics for device engineering. Using a combination of epitaxial growth techniques in conjunction with theoretical approaches, we show the formation of a morphotropic phase boundary through epitaxial constraint in lead-free piezoelectric bismuth ferrite (BiFeO3) films. Electric field-dependent studies show that a tetragonal-like phase can be reversibly converted into a rhombohedral-like phase, accompanied by measurable displacements of the surface, making this new lead-free system of interest for probe-based data storage and actuator applications.
Above-bandgap voltages from ferroelectric photovoltaic devices
(2010-02-01)
Yang, S. Y.
;
Seidel, J.
;
Byrnes, S. J.
;
Shafer, P.
;
Yang, C. -H.
In conventional solid-state photovoltaics, electron-hole pairs are created by light absorption in a semiconductor and separated by the electric field spaning a micrometre-thick depletion region. The maximum voltage these devices can produce is equal to the semiconductor electronic bandgap. Here, we report the discovery of a fundamentally different mechanism for photovoltaic charge separation, which operates over a distance of 1-2 nm and produces voltages that are significantly higher than the bandgap. The separation happens at previously unobserved nanoscale steps of the electrostatic potential that naturally occur at ferroelectric domain walls in the complex oxide BiFeO(3). Electric-field control over domain structure allows the photovoltaic effect to be reversed in polarity or turned off. This new degree of control, and the high voltages produced, may find application in optoelectronic devices.
Advances in the growth and characterization of magnetic, ferroelectric, and multiferroic oxide thin films
(2010-05-20)
Martin, L. W.
;
Chu, Y-H.
;
Ramesh, R.
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The growth and characterization of functional oxide thin films that are ferroelectric, magnetic, or both at the same time are reviewed. The evolution of synthesis techniques and how advances in in situ characterization have enabled significant acceleration in improvements to these materials are described. Methods for enhancing the properties of functional materials or creating entirely new functionality at interfaces are covered, including strain engineering and layering control at the atomic-layer level. Emerging applications of these functional oxides such as achieving electrical control of ferromagnetism and the future of these complex functional oxides is discussed. (C) 2010 Elsevier B.V. All rights reserved.
Conduction at domain walls in oxide multiferroics
(2009-03-01)
Seidel, J.
;
Martin, L. W.
;
He, Q.
;
Zhan, Q.
;
Chu, Y. -H.
Domain walls may play an important role in future electronic devices, given their small size as well as the fact that their location can be controlled. Here, we report the observation of room-temperature electronic conductivity at ferroelectric domain walls in the insulating multiferroic BiFeO(3). The origin and nature of the observed conductivity are probed using a combination of conductive atomic force microscopy, high-resolution transmission electron microscopy and first-principles density functional computations. Our analyses indicate that the conductivity correlates with structurally driven changes in both the electrostatic potential and the local electronic structure, which shows a decrease in the bandgap at the domain wall. Additionally, we demonstrate the potential for device applications of such conducting nanoscale features.
Critical thickness and orbital ordering in ultrathin La(0.7)Sr(0.3)MnO(3) films
(2008-09-01)
Huijben, M.
;
Martin, L. W.
;
Chu, Y. -H.
;
Holcomb, M. B.
;
Yu, P.
Detailed analysis of transport, magnetism, and x-ray absorption spectroscopy measurements on ultrathin La(0.7)Sr(0.3)MnO(3) films with thicknesses from 3 to 70 unit cells resulted in the identification of a lower critical thickness for a nonmetallic nonferromagnetic layer at the interface with the SrTiO(3) (001) substrate of only three unit cells (similar to 12 angstrom). Furthermore, linear-dichroism measurements demonstrate the presence of a preferred (x(2)-y(2)) in-plane orbital ordering for all layer thicknesses without any orbital reconstruction at the interface. A crucial requirement for the accurate study of these ultrathin films is a controlled growth process, offering the coexistence of layer-by-layer growth and bulklike magnetic/transport properties.
Critical thickness and orbital ordering in ultrathin La0.7Sr0.3MnO3 films
(2008-09-01)
Huijben, M.
;
Martin, L. W.
;
Chu, Y. -H.
;
Holcomb, M. B.
;
Yu, P.
Detailed analysis of transport, magnetism, and x-ray absorption spectroscopy measurements on ultrathin La0.7Sr0.3MnO3 films with thicknesses from 3 to 70 unit cells resulted in the identification of a lower critical thickness for a nonmetallic nonferromagnetic layer at the interface with the SrTiO3 (001) substrate of only three unit cells (similar to 12 angstrom). Furthermore, linear-dichroism measurements demonstrate the presence of a preferred (x(2)-y(2)) in-plane orbital ordering for all layer thicknesses without any orbital reconstruction at the interface. A crucial requirement for the accurate study of these ultrathin films is a controlled growth process, offering the coexistence of layer-by-layer growth and bulklike magnetic/transport properties.
Electric modulation of conduction in multiferroic Ca-doped BiFeO(3) films
(2009-06-01)
Yang, C. -H.
;
Seidel, J.
;
Kim, S. Y.
;
Rossen, P. B.
;
Yu, P.
Many interesting materials phenomena such as the emergence of high-T(c) superconductivity in the cuprates and colossal magnetoresistance in the manganites arise out of a doping-driven competition between energetically similar ground states. Doped multiferroics present a tantalizing evolution of this generic concept of phase competition. Here, we present the observation of an electronic conductor-insulator transition by control of band-filling in the model antiferromagnetic ferroelectric BiFeO(3) through Ca doping. Application of electric field enables us to control and manipulate this electronic transition to the extent that a p-n junction can be created, erased and inverted in this material. A 'dome-like' feature in the doping dependence of the ferroelectric transition is observed around a Ca concentration of similar to 1/8, where a new pseudo-tetragonal phase appears and the electric modulation of conduction is optimized. Possible mechanisms for the observed effects are discussed on the basis of the interplay of ionic and electronic conduction. This observation opens the door to merging magnetoelectrics and magnetoelectronics at room temperature by combining electronic conduction with electric and magnetic degrees of freedom already present in the multiferroic BiFeO(3).
Electric modulation of conduction in multiferroic Ca-doped BiFeO3 films
(2009-06-01)
Yang, C. -H.
;
Seidel, J.
;
Kim, S. Y.
;
Rossen, P. B.
;
Yu, P.
Many interesting materials phenomena such as the emergence of high-T-c superconductivity in the cuprates and colossal magnetoresistance in the manganites arise out of a doping-driven competition between energetically similar ground states. Doped multiferroics present a tantalizing evolution of this generic concept of phase competition. Here, we present the observation of an electronic conductor-insulator transition by control of band-filling in the model antiferromagnetic ferroelectric BiFeO3 through Ca doping. Application of electric field enables us to control and manipulate this electronic transition to the extent that a p-n junction can be created, erased and inverted in this material. A 'dome-like' feature in the doping dependence of the ferroelectric transition is observed around a Ca concentration of similar to 1/8, where a new pseudo-tetragonal phase appears and the electric modulation of conduction is optimized. Possible mechanisms for the observed effects are discussed on the basis of the interplay of ionic and electronic conduction. This observation opens the door to merging magnetoelectrics and magnetoelectronics at room temperature by combining electronic conduction with electric and magnetic degrees of freedom already present in the multiferroic BiFeO3.
Interface control of bulk ferroelectric polarization
(2012-06-19)
Yu, P.
;
Luo, W.
;
Yi, D.
;
Zhang, J. X.
;
Rossell, M. D.
The control of material interfaces at the atomic level has led to novel interfacial properties and functionalities. In particular, the study of polar discontinuities at interfaces between complex oxides lies at the frontier of modern condensed matter research. Here we employ a combination of experimental measurements and theoretical calculations to demonstrate the control of a bulk property, namely ferroelectric polarization, of a heteroepitaxial bilayer by precise atomic-scale interface engineering. More specifically, the control is achieved by exploiting the interfacial valence mismatch to influence the electrostatic potential step across the interface, which manifests itself as the biased-voltage in ferroelectric hysteresis loops and determines the ferroelectric state. A broad study of diverse systems comprising different ferroelectrics and conducting perovskite underlayers extends the generality of this phenomenon.
Interface Ferromagnetism and Orbital Reconstruction in BiFeO(3)-La(0.7)Sr(0.3)MnO(3) Heterostructures
(2010-07-06)
Yu, P.
;
Lee, J. -S.
;
Okamoto, S.
;
Rossell, M. D.
;
Huijben, M.
We report the formation of a novel ferromagnetic state in the antiferromagnet BiFeO(3) at the interface with ferromagnet La(0.7)Sr(0.3)MnO(3). Using x-ray magnetic circular dichroism at Mn and Fe L(2,3) edges, we discovered that the development of this ferromagnetic spin structure is strongly associated with the onset of a significant exchange bias. Our results demonstrate that the magnetic state is directly related to an electronic orbital reconstruction at the interface, which is supported by the linearly polarized x-ray absorption measurement at the oxygen K edge.
Interface Ferromagnetism and Orbital Reconstruction in BiFeO3-La0.7Sr0.3MnO3 Heterostructures
(2010-07-06)
Yu, P.
;
Lee, J. -S.
;
Okamoto, S.
;
Rossell, M. D.
;
Huijben, M.
We report the formation of a novel ferromagnetic state in the antiferromagnet BiFeO3 at the interface with ferromagnet La0.7Sr0.3MnO3. Using x-ray magnetic circular dichroism at Mn and Fe L-2,L-3 edges, we discovered that the development of this ferromagnetic spin structure is strongly associated with the onset of a significant exchange bias. Our results demonstrate that the magnetic state is directly related to an electronic orbital reconstruction at the interface, which is supported by the linearly polarized x-ray absorption measurement at the oxygen K edge.
Large field-induced strains in a lead-free piezoelectric material
(2011-02-01)
Zhang, J. X.
;
Xiang, B.
;
He, Q.
;
Seidel, J.
;
Zeches, R. J.
Piezoelectric materials exhibit a mechanical response to electrical inputs, as well as an electrical response to mechanical inputs, which makes them useful in sensors and actuators(1). Lead-based piezoelectrics demonstrate a large mechanical response, but they also pose a health risk(2). The ferroelectric BiFeO(3) is an attractive alternative because it is lead-free, and because strain can stabilize BiFeO(3) phases with a structure that resembles a morphotropic phase boundary(3). Here we report a reversible electric-field-induced strain of over 5% in BiFeO(3) films, together with a characterization of the origins of this effect. In situ transmission electron microscopy coupled with nanoscale electrical and mechanical probing shows that large strains result from moving the boundaries between tetragonal- and rhombohedral-like phases, which changes the phase stability of the mixture. These results demonstrate the potential of BiFeO(3) as a substitute for lead-based materials in future piezoelectric applications.
Magnetotransport at Domain Walls in BiFeO3
(2012-02-09)
He, Q.
;
Yeh, C-H.
;
Yang, J-C.
;
Singh-Bhalla, G.
;
Liang, C-W.
Domain walls in multiferroics can exhibit intriguing behaviors that are significantly different from the bulk of the material. We investigate strong magnetoresistance in domain walls of the model multiferroic BiFeO3 by probing ordered arrays of 109 degrees domain walls with temperature-and magnetic-field-dependent transport. We observe temperature-dependent variations in the transport mechanism and magnetoresistances as large as 60%. These results suggest that by locally breaking the symmetry of a material, such as at domain walls and structural interfaces, one can induce emergent behavior with properties that deviate significantly from the bulk.
Optical properties and magnetochromism in multiferroic BiFeO(3)
(2009-04-01)
Xu, X. S.
;
Brinzari, T. V.
;
Lee, S.
;
Chu, Y. H.
;
Martin, L. W.
In order to investigate spin-charge coupling in multiferroic oxides, we measured the optical properties of BiFeO(3). Although the direct 300 K charge gap is observed at 2.67 eV, absorption onset actually occurs at much lower energy with Fe(3+) excitations at 1.41 and 1.90 eV. Temperature and magnetic-field-induced spectral changes reveal complex interactions between on-site crystal-field and magnetic excitations in the form of magnon sidebands. We employ the sensitivity of these magnon sidebands to map out the magnetic-field-temperature phase diagram which demonstrates optical evidence for spin spiral quenching above 20 T and suggests a spin domain reorientation near 10 T.
Optical properties and magnetochromism in multiferroic BiFeO3
(2009-04-01)
Xu, X. S.
;
Brinzari, T. V.
;
Lee, S.
;
Chu, Y. H.
;
Martin, L. W.
In order to investigate spin-charge coupling in multiferroic oxides, we measured the optical properties of BiFeO3. Although the direct 300 K charge gap is observed at 2.67 eV, absorption onset actually occurs at much lower energy with Fe3+ excitations at 1.41 and 1.90 eV. Temperature and magnetic-field-induced spectral changes reveal complex interactions between on-site crystal-field and magnetic excitations in the form of magnon sidebands. We employ the sensitivity of these magnon sidebands to map out the magnetic-field-temperature phase diagram which demonstrates optical evidence for spin spiral quenching above 20 T and suggests a spin domain reorientation near 10 T.
Orientation-dependent potential barriers in case of epitaxial Pt-BiFeO(3)-SrRuO(3) capacitors
(2009-06-08)
Pintilie, L.
;
Dragoi, C.
;
Chu, Y. H.
;
Martin, L. W.
;
Ramesh, R.
The leakage current in epitaxial BiFeO(3) capacitors with bottom SrRuO(3) and top Pt electrodes, grown by pulsed laser deposition on SrTiO(3) (100), SrTiO(3) (110), and SrTiO(3) (111) substrates, is investigated by current-voltage (I-V) measurements in the 100-300 K temperature range. It is found that the leakage current is interface-limited and strongly dependent on the orientation of the substrate. The potential barriers at the electrode interfaces are estimated to about 0.6, 0.77, and 0.93 eV for the (100), (110), and (111) orientations, respectively.
Orientation-dependent potential barriers in case of epitaxial Pt-BiFeO3-SrRuO3 capacitors
(2009-06-08)
Pintilie, L.
;
Dragoi, C.
;
Chu, Y. H.
;
Martin, L. W.
;
Ramesh, R.
The leakage current in epitaxial BiFeO3 capacitors with bottom SrRuO3 and top Pt electrodes, grown by pulsed laser deposition on SrTiO3 (100), SrTiO3 (110), and SrTiO3 (111) substrates, is investigated by current-voltage (I-V) measurements in the 100-300 K temperature range. It is found that the leakage current is interface-limited and strongly dependent on the orientation of the substrate. The potential barriers at the electrode interfaces are estimated to about 0.6, 0.77, and 0.93 eV for the (100), (110), and (111) orientations, respectively.
Photovoltaic effects in BiFeO(3)
(2009-08-10)
Yang, S. Y.
;
Martin, L. W.
;
Byrnes, S. J.
;
Conry, T. E.
;
Basu, S. R.
We report a photovoltaic effect in ferroelectric BiFeO(3) thin films. The all-oxide heterostructures with SrRuO(3) bottom and tin doped indium oxide top electrodes are characterized by open-circuit voltages similar to 0.8-0.9 V and external quantum efficiencies up to similar to 10% when illuminated with the appropriate light. Efficiencies are at least an order of magnitude larger than the maximum efficiency under sunlight (AM 1.5) thus far reported for ferroelectric-based devices. The dependence of the measured open-circuit voltage on film thickness suggests contributions to the large open-circuit voltage from both the ferroelectric polarization and band offsets at the BiFeO(3)/tin doped indium oxide interface.
Photovoltaic effects in BiFeO3
(2009-08-10)
Yang, S. Y.
;
Martin, L. W.
;
Byrnes, S. J.
;
Conry, T. E.
;
Basu, S. R.
We report a photovoltaic effect in ferroelectric BiFeO3 thin films. The all-oxide heterostructures with SrRuO3 bottom and tin doped indium oxide top electrodes are characterized by open-circuit voltages similar to 0.8-0.9 V and external quantum efficiencies up to similar to 10% when illuminated with the appropriate light. Efficiencies are at least an order of magnitude larger than the maximum efficiency under sunlight (AM 1.5) thus far reported for ferroelectric-based devices. The dependence of the measured open-circuit voltage on film thickness suggests contributions to the large open-circuit voltage from both the ferroelectric polarization and band offsets at the BiFeO3/tin doped indium oxide interface.