Symposium Organizers
Gopalan Srinivasan Oakland University
Mirza I. Bichurin Novgorod State University
Shashank Priya Virginia Tech
Nian X. Sun Northeastern University
I2: Composite Multiferroics
Session Chairs
Tuesday PM, April 14, 2009
Room 2012 (Moscone West)
2:30 PM - **I2.1
Fabrication and Properties of Multiferroic Nanowire Heterostructures
Arunava Gupta 1 , Gunwoo Kim 2 , Alexander Tatarenko 3 , Gopalan Srinivasan 3
1 MINT Center and Department of Chemistry, University of Alabma, Tuscaloosa, Alabama, United States, 2 MINT Center and Department of Electrical and Computer Engineering, University of Alabama, Tuscaloosa, Alabama, United States, 3 Department of Physics, Oakland University, Oakland, Michigan, United States
Show Abstract The coupling of magnetic and electronic properties, referred to as the magneto-electric (ME) effect, allows for dual functionality in a single-phase or composite material system. For example, an applied electric or magnetic field will induce a magnetization or polarization response and in a composite system the response is mediated by mechanical stress: magnetostriction induced mechanical deformation and piezoelectric effect induced electric fields [1]. Unlike bulk samples, the ME coupling in thin films is typically weak due to the strong substrate clamping effect. We have fabricated and studied the properties of nanowires (1D) consisting of ferroelectric barium titanate (BTO), with ferrimagnetic nickel iron oxide (NFO). The work is motivated by our recent theoretical studies that suggest strong ME interaction in such nanostructures [2]. A chemical vapor deposition process has been developed for the growth of single crystalline magnesium oxide (MgO) nanowires [3]. The vertical MgO nanowires are used as a template for the coaxial growth of BTO and NFO using pulsed laser deposition. High resolution TEM images have confirmed the heteroepitaxial growth. We have used electrostatic force microscopy (EFM) and magnetic force microscopy (MFM) to probe the ferroelectric and magnetic response of the nanowires. Four-point probe measurements of the frequency-dependent ME properties of individual nanowires are obtained using e-beam patterned contact pads. References: [1] W. Eerenstein, N.D Mathur, and J. F. Scott, Nature 442, 759, 2006; [2] V. Petrov, G. Srinivasan, M. I. Bichurin, and A. Gupta, Phys. Rev. B 75, 224407 (2007); [3] G. Kim, R. L. Martens, G. B. Thompson, B. C. Kim, and A. Gupta , J. Appl. Phys. 102, 104906 (2007).
3:00 PM - I2.2
Growth of Epitaxial ZnO:Mn/ZnO:V Heterostructures and Ferroelectric-ferromagnetic Characterization.
Devajyothi Mukherjee 1 , Tara Dhakal 1 , Hariharan Srikanth 1 , Pritish Mukherjee 1 , Sarath Witanachchi 1
1 Department of Physics, University of South Florida, Tampa, Florida, United States
Show AbstractThe wide band gap semiconductor ZnO is well known for its multifunctionality in the form of ferromagnetism, piezoelectricity, and magneto optics. ZnO has been found to grow with intrinsic oxygen deficiencies which in turn are believed to give ferromagnetism and high conductivity in this material. Doping divalent cation Zn sites by penta-valent V ions creates a mixed valency as well as strain in the original ZnO hexagonal structure because of the reduced ionic size of vanadium. The mixed valency creates charge polarity between Zn-O and V-O bonds. This charge polarity and the rotation of the nonlinear V-O bonds w.r.t. Zn-O bonds under electric field has been shown to produce ferroelectricity. Furthermore, Mn doping of ZnO has also shown enhancement in ferromagnetic properties in ZnO. For this material to be a viable ferromagnetic material the magnetic properties should not be from segregated phases. In the present study we have grown undoped, Mn, and V doped ZnO thin films using pulsed laser deposition (PLD). ZnO target with 1% atomic Mn doping and a target with 0.5% atomic V doping were prepared by solid state reactions and sintering. Films were grown both epitaxially on sapphire substrates and in polycrystalline form on silicon substrates. The growth pressures were varied from 10 mT to 300 mT while growth temperatures were varied from room temperature to 600oC. Both θ-2θ and Φ-scans of x-ray diffraction showed epitaxial growth on sapphire substrates. Magnetization measurements by the PPMS showed M vs. H hysteresis loops with saturation for all ZnO: Mn films. V doped films showed high saturation polarization for film deposited at high pressures. We have also fabricated epitaxial bilayers of ZnO:V/ZnO:Mn on sapphire substrates. Ferroelectric and ferromagnetic properties of these heterostructures will be presented.
3:15 PM - I2.3
Growth and Structural Characterization of La0.8Sr0.2MnO3/BaTiO3 Superlattice on SrTiO3 (001) Single Crystal Substrate.
Zhen Yang 1 , Chang Ke 1 , Wei Chen 1 , Wei Guang Zhu 1
1 Microelectronics Center, Nanyang Technological University, School of Electrical & Electronic Engineering, Singapore Singapore
Show AbstractTransition metal oxides with perovskite structure exhibit interesting properties, and those superlattice structures and properties can be tailored for a wide variety of applications such as electronic and opto-electronic devices, recording medium and spintronics. There are very few ‘multiferroic’ materials in nature that exhibit both of ferroelectric (FE) and ferromagnetic (FM) properties, but the coupling between ferroelectricity and magnetism is weak. . An alternative approach is to introduce two phase systems in composite structure, and each phase can be independently optimized and tailored for its desired performance. La1-xSrxMnO3 (LSMO) and BaTiO3 (BTO) are typical representatives in t FM and FE materials, respectively. In this paper, we report the nano-configured LSMO/BTO super-lattice to realize the strong coherence between FE and FM properties. Variety of LSMO/BTO super-lattices have been grown on SrTiO3 (001) single crystal substrate using laser molecular beam epitaxy technique. In situ growth conditions were monitored by reflection high energy electron diffraction (RHEED) for mono-layer growth and crystallization characterization was carried out by high resolution X-ray diffraction (XRD). The fully strained epitaxial structures were evidenced by asymmetric reciprocal space mapping, and the result shown the growth direction in parallel to [100]. The full width at half maximum (FWHM) of X-ray rocking curve measurement around the satellite peak of the super-lattice yielded only 0.005 degree, indicating the nearly perfect crystal plane and sharp interface.
3:30 PM - I2:Composite
BREAK
4:00 PM - I2.4
Diblock Copolymer Based Self-Assembled Nano-Magneto-Electric.
Shenqiang Ren 1 , Manfred Wuttig 1
1 Materials and Science Engineering Department, University of Maryland at College Park, College park, Maryland, United States
Show AbstractA magnetoelectric (ME) composite consisting of hexagonally arranged ferromagnetic CoFe2O4 nano-cylinders within a matrix of ferroelectric PZT has been synthesized using co-assembly of two inorganic precursors with a block copolymer. Films of this material were spun onto electroded substrates and annealed for crystallization. The initial magnetic permeability of the self-assembled CFO/PZT nano-composite changes by a factor of five through the application of 2.5 V1. In this talk, this and self-assembled lamellar ordered magnetoelectric nanostructures will be discussed. "1, S. Ren, R. Briber and M. Wuttig, APL 93, X (2008)"
4:15 PM - I2.5
Charge-mediated Magnetoelectric Coupling in Composite Multiferroics.
Jason Hoffman 1 2 , Carlos Vaz 1 2 , Hajo Molegraaf 3 4 , Jean-Marc Triscone 3 , Charles Ahn 1 2
1 Applied Physics, Yale University, New Haven, Connecticut, United States, 2 Center for Research on Interface Structure and Phenomenon, Yale University, New Haven, Connecticut, United States, 3 DPMC, Université de Genève, Geneva Switzerland, 4 , University of Twente, Enschede Netherlands
Show AbstractRecent efforts to exploit materials with multifunctional capabilities have renewed interest in multiferroics, which display a coupling between ferroic order parameters. Engineered structures that combine dissimilar magnetic and ferroelectric systems epitaxially have been shown to exhibit enhanced magnetoelectric coupling. In this work, we employ magneto-optic Kerr effect (MOKE) magnetometry to demonstrate direct control of magnetism in epitaxial ferroelectric Pb(Zr,Ti)O3 (PZT) / La0.8Sr0.2MnO3 (LSMO) heterostructures, including a charge-mediated shift in the magnetic Curie temperature and on/off switching of magnetism. Through M-E (magnetization vs. electric field) measurements we obtain a magnetoelectric coupling coefficient of ~ 1 Oe cm / kV. In contrast to chemical doping, this approach allows one to achieve carrier-mediated control of magnetism in a reversible fashion without introducing lattice disorder or distortion.
4:30 PM - I2.6
Multiferroic Properties in Epitaxial [Self Assembled BiFeO3 - γ-Fe2O3 Nanocomposite] - Bi3.25La0.75Ti3O12 Bi-layers.
Olivier Gautreau 1 , Catalin Harnagea 1 , Lina Gunawan 2 , Gianluigi Botton 2 , Alain Pignolet 1
1 INRS-Energie Materiaux et Telecommunications, Universite du Quebec, Varennes, Quebec, Canada, 2 Brockhouse Institute for Materials Research and Centre for Emerging Device Technologies, Mc Master University, Hamilton, Ontario, Canada
Show AbstractBiFeO3 (BFO) is a multiferroic perovskite (ferroelectric and antiferromagnetic with a weak ferromagnetic component due to spin canting), with high ferroelectric Curie (850 °C) and magnetic Neel (370 °C) temperatures. Hence, BFO thin films are one of the best candidates for applications at room temperature (e.g. spintronic data storage media, multiple-state memories). However they commonly exhibit both a too low resistivity and a too weak magnetic moment to reach the ferroelectric and magnetic performances required for applications. To overcome those drawbacks we designed epitaxial heterostructures comprising a self-assembled complex oxides nanocomposite layer (i.e. BiFeO3 - γ-Fe2O3 or BFO-FO) and a Bi-layered perovskite (i.e. Bi3.25La0.75Ti3O12 or BLT) layer. BLT layers are ferroelectric insulating layers preventing charges migration from BFO-FO layers to the electrodes, increasing the resistivity; and since BLT has a high lattice mismatch with BFO, under specific conditions, BFO phase relaxes the compressive elastic strain imposed by heteroepitaxy by BLT and promotes the development of epitaxial inclusions of magnetic γ-Fe2O3 phase at BFO grain boundaries increasing the resultant magnetic moment [1]. We will show that such composite bi-layers (BFO-FO/BLT and BLT/BFO-FO) exhibit at room temperature the coexistence of good ferroelectric and magnetic properties [1]. Ferroelectricity and magnetism are conserved at the nanoscale, whereby ferroelectricity is mostly provided by the BFO matrix and ferrimagnetism by the FO inclusions. The epitaxial [self assembled BiFeO3 - γ-Fe2O3 nanocomposite] - Bi3.25La0.75Ti3O12 bi-layered heterostructures have been synthesized by Pulsed Laser Deposition (PLD). Structural characterization was performed by High Resolution X-ray Diffraction (HR-XRD), Transmission Electron Microscopy (TEM), and Atomic Force Microscopy (AFM), while the functional properties were characterized by using a ferroelectric tester, Piezoresponse Force Microscopy (PFM), Superconducting Quantum Interference Device (SQUID) magnetometry, as well as Magnetic Force Microscopy (MFM). The details of the multiferroic properties (ferroelectric switching characteristics, ferroelectric imprint, magnetic moment amplitude, magnetic easy axis direction) will be discussed as well as how they are directly related to the microstructure (crystallites size, grains morphology) of the BFO-FO layers induced by different strain states at both the top and bottom interfaces of the BFO-FO layers. [1] O. Gautreau et al.; J. Phys. D, 41, 112002 (2008)
4:45 PM - I2.7
Multiferroic Nanofibers by Sol-Gel based Electrospinning.
Shuhong Xie 2 , Jiangyu Li 1 , Yichun Zhou 2
2 Key Laboratory of Low Dimensional Materials & Application Technology of Ministry of Education, and Faculty of Materials, Optoelectronics and Physics, Xiangtan University, Xiangtan China, 1 , University of Washington, Seattle, Washington, United States
Show AbstractMultiferroic materials possess two or more types of orders simultaneously that couple the electric and magnetic fields, and both composite multiferroics consisting of ferroelectric and ferromagnetic phases and single-phase multiferroic bismuth ferrite have been widely explored for their excellent multiferroic properties and magnetoelectric coupling. In this talk, we present both CoFe2O4-Pb(Zr0.52Ti0.48)O3 composite nanofibers and single-phase BiFeO3 nanofibers synthesized by sol-gel based electrospinning. Excellent crystalline structure and crystallinity of the nanofibers have been verified by XRD, SEM, TEM, and HRTEM, and the coexistence of ferroelectric and ferromagnetic properties have been confirmed by piezoresponse force microscopy and VSM hysteresis measurement. These novel nanofibers we developed could enable multiferroic devices at nanoscale.
5:00 PM - I2.8
ME Thin Film Composites using TbFe/FeCo Multilayers.
Henry Greve 1 , Andre Piorra 1 , Antonio Malave 1 , Eckhard Quandt 1
1 Materials Science, University of Kiel, Kiel Germany
Show AbstractGiant magnetoelectric (ME) effects of certain magnetostrictive/piezoelectric composites are of increasing interest due to their high ME coefficients compared to single phase materials. This paper describes recent results that were obtained for sputtered highly magnetostrictive TbFe/FeCo multilayers on different piezoelectric materials. Using intrinsic and induced magnetic anisotropies can result in a pronounced directional dependency of the ME effect. Thin magnetic films display anisotropies that are induced by the demagnetization field that lead to a reduction of the “out of plane” ME coefficient. “In-plane” ME effects can be influenced by annealing and field-cooling leading to a pronounced easy and hard axes in the magnetostrictive multilayers. In case of a perfect alignment the magnetostriction of the TbFe/FeCo multilayers along the easy axis vanishes and thus the ME effect is restricted to external in-plane magnetic fields with a field component in direction of the hard axis. Furthermore, this magnetic field annealing increases the magnetostriction in the hard axis direction and decreases the magnetic saturation field thus resulting in an overall increase in magnetostrictive susceptibility and corresponding of the ME coefficient. The experimental results will be discussed in view of the observed magnetic domain structures as well as their potential use for a magnetic vector field sensor.
I3: Poster Session: Multiferroics
Session Chairs
Tuesday PM, April 14, 2009
Exhibition Hall (Moscone West)
6:00 PM - I3.1
Synthesis of Monodispersed Multiferroic BiFeO3 Nanocrystals.
Jun Wang 1 , Zhiqun Lin 1
1 Department of Materials Science and Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractMonodispersed multiferroic bismuth ferrite (BiFeO3, BFO) nanoparticles were synthesized via a nonhydrolytic thermal decomposition approach. Our method involved the formation of metal (i.e. Bi, Fe) oleate from metal oxide and oleic acid, followed by subsequent high temperature thermal decomposition of metal oleate with existence of surfactant (i.e. oleic acid). The obtained BFO nanoparticles were characterized by TEM, exhibiting monodispersed size distribution. The chemical composition of nanoparticles was analyzed by EDX; and their crystalline structures were examined by X-ray powder diffraction and high resolution TEM. The size of BFO nanoparticles could be readily controlled by the thermal decomposition temperature. The size-dependent properties of monodispersed BFO nanoparticles synthesized at different temperature were studied.
6:00 PM - I3.10
Magnetoelectric Effect in Bilayered Composites of Giant Magnetostrictive Layer and Lead-free Ceramic.
Jing Ma 1 , Jiamian Hu 1 , Ce-Wen Nan 1
1 , Tsinghua University, Beijing China
Show AbstractLead-free piezoelectric ceramics, which do not give rise to lead contamination, have undergone an intensive worldwide research in recent years. Similar to lead-based magnetoelectric (ME) composites, the composites containing lead-free piezoelectric phase and giant magnetostrictive phase can also exhibit an electric polarization in magnetic field, showing widely applications as magnetic field sensors, especially in the biological and medical fields. In this work, a bilayered structure of KNLNS-x ceramic chip and Terfenol-D/epoxy mixture layer is investigated. The composites exhibited the maximum ME voltage coefficient of 16 mV/cmOe at low frequency and 1.5 V/cmOe at the resonance frequency under a dc magnetic bias of 2 kOe. The ME effect was analyzed and found to be comparable to most major lead-based ME composites, and can be enhanced by optimizing the configuration and thickness ratio of the bilayer. The present study opens up possibilities for developing green ME devices.
6:00 PM - I3.11
Magnetoelectric Phenomena in Bismuth-substituted Ferrite Garnet Films in External Electric Field.
Koronovskyy Vadim 1 , Kalenichenko Oleksandr 1
1 Department of Radiophysics, Taras Shevchenko Kiev National University, Kiev Ukraine
Show AbstractMagneto-electric properties of bismuth-substituted ferrite-garnet films have been investigated by using optical polarimetry method, electromagneto-optical (EMO) effect [1]. The heart of the experimental method is the registration of the electric-field-induced changes of the Faraday rotation in crystals – α (EMOE) [2]. Taking into account high sensitivity of EMOE to changes in structural characteristics of magnetoelectrics [3], researches of influence of pulse laser irradiation on character of magnetoelectric dependences of EMOE has been carried out in geometry E perpendicularly for k, H || k, where k is a light wave vector, E and H - electric and magnetic field intensity.Powerful laser irradiation is considered as a means of purposeful updating of physical characteristics of the research object, in particular, as a means of influence for nonuniform pressure in films. For irradiation of the film, we used pulse neodim laser (λ=1,06 μm, τ=2 milliseconds), we used irradiation in the range of a transparency for ferrite garnets. When the film was irradiated by laser impulse with density of energy 20 and 40 J/Cm2, we did not observe essential changes in the field dependence of the Faraday rotation in film in comparison to the dependence measured before an irradiation, i.e., the specified density of energy of an irradiation is not enough for change of magnetic properties of this film. However, changes of EMOE value in separate multidomain areas of the film were observed. It is especially interesting, that when the value of impulse was 40 J/Cm2, the α (EMO) in a maximum (on given site of the film) almost twice has exceeded the value of EMOE registered before an irradiation. In our opinion, such a strong change of EMOE, at an irradiation by laser impulse, has the following explanation. At formation of epitaxial films, micro- and macropressure deformations arise. On the film volume, there can be local sites or thin layers where centrosymmetric structure (which is characteristic for single crystal of ferrite garnets) is broken. The powerful laser impulse can remove or partially remove local mechanical strain. It is known that square-law on E-field EMOE is characteristic only for centrosymmetric magnetoelectrics [1]. The increase or decrease of EMOE value at the same site of sample can testify changing in centrosymmetric structure of the sample. In particular the increase of EMOE can be a reaction to removal of local mechanical strain in centrosymmetric magnetoelectrics.REFERENCES [1] B. B. Krichevtsov, R. V. Pisarev, A. G. Selitskij, JETP Lett. 41, 317 (1985)[2] V. E. Koronovskyy, S. M. Ryabchenko, V. F. Kovalenko, Phys. Rev. B 71, 172402 (2005)[3] V. E. Koronovskyy, Phys. Stat. Sol. (a) 203, No. 8, 2007 (2006)
6:00 PM - I3.12
Templated Fabrication and Characterization of Fe Nanowire in SiO2 Nanotube
Tawab Dastagir 1 , Hongbin Yu 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractIn this study Fe nanowires in SiO2 nanotubes embedded in anodic alumina oxide (AAO) template have been fabricated and characterized. Ferromagnetic nanowires have attracted much attention due to their potential technological applications as magnetic recording media, nanosensors and biomedical applications such as magnetic resonance imaging (MRI) and magnetic transport of biomedical complexes. Several methods have been reported to fabricate metallic nanowires such as electron beam lithography and focus ion beam milling, electroless procedure and electrodeposition in nanoporous templates. Among the methods reported, the template method is the simplest and most versatile method. Anodized aluminum oxides (AAO) template is one of the desirable templates because of its good mechanical strength and thermal stability, tunable pore dimension, low cost and high yield technique for producing large arrays of nanowires. Magnetic materials have a tendency to be oxidized in ambient condition. These oxidized magnetic materials are not acceptable in many applications specially in biomedical applications. To avoid this oxidation, researchers have been trying to coat the nanowires with different compounds such as Au, SiO2, and ZnO. Idea is to make nanoscale core-shell structure first and then to grow nanowires inside the shell. But coating has to be such that it does not interfere with the magnetic properties of the materials. Here we first grow 6-8 nm thick SiO2 nanotubes inside the template using “surface sol-gel” technique. Then Fe nanowires are synthesized using electrodeposition technique inside these SiO2 nanotubes. The nanotube structures were characterized by field emission scanning electron microscopy (FESEM) and energy dispersive analysis using x-rays (EDAX). Magnetic properties of the SiO2 insulated Fe nanowires inside the membrane are characterized by Superconducting Quantum Interference Device (SQUID). Relative high coercivities of about 120 Oe at field parallel to the nanowire arrays and 230 Oe at field perpendicular the nanowires are achieved at room temperature. The magnetic hysteresis loop suggests that the SiO2 insulated nanowires have the uniaxial magnetic anisotropy with the easy magnetization direction along the nanowire arrays due to their large shape anisotropy. As these SiO2 insulated magnetic nanowires have good magnetic properties, these insulated magnetic nanowires can be used in different microelectronics and biomedical application.
6:00 PM - I3.13
Height Dependent Magnetic Force Microscopy Study of Nickel Magnetic Nanowires.
Tawab Dastagir 1 , Hongbin Yu 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractThe study of magnetic nanostructures is of great interest due to their potential applications in ultrahigh density storage and logic functions. In this work, we electrochemically synthesized nickel nanowires inside anodic alumina oxide (AAO). The diameter of these nanowires ranges between 100nm to 200nm. Anodization processes to achieve self-ordered nanopores in membrane have been proven to be a direct, simple, nonexpensive technique to fabricate templates for highly ordered densely packed arrays of magnetic nanowires. Magnetic force microscopy (MFM) imaging is a very powerful technique to locally study the magnetic state of nanostructures which allow imaging with the spatial resolution of 10-100nm. MFM has been used to characterize the magnetic state of the synthesized nanowires. In MFM, the magnetic contrast is obtained through detecting the force gradient between a ferromagnetic tip and the magnetic sample by amplitude, phase or frequency detection techniques. In this work we have used Lift Mode with phase detection technique to obtain magnetic imaging at different tip height ranging from 25nm to 100nm. We have found that magnetic contrast of these nanowires changes with tip height. Object Oriented Micro Magnetic Framework (OOMMF) simulation have been performed to study these changes. The signal measured by magnetic-force microscopy is proportional to the second derivative of the z component of the stray field in z-direction. In OOMMF simulation this second derivative of the z component of the stray field in z-direction at different heights has been simulated. These simulation results have been used to explain the different MFM images at different tip height.
6:00 PM - I3.14
Room Temperature Single Phase Multiferroics Pb{(Zr1/2Ti1/2)x(Fe1/2Ta1/2)1-x}O3 Ceramics.
Dilsom Sanchez 1 , Ricardo Martinez 1 , Ashok Kumar 1 , Ram Katiyar 1
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractThe polycrystalline Pb{(Zr1/2Ti1/2)1-x(Fe1/2Ta1/2)x}O3 (PZTFT) (x = 0.1, 0.2, 0.3, 0.4) ceramics samples were synthesized by a mechanosynthesis (i.e. high-energy ball milling) route followed by a mixed oxide method using solid state technique,. X-ray diffraction (XRD) patterns of all compositions showed single phase at room temperature without any pyrochlore phase. Well defined grains with average grain size of more than 1 μm were observed from Secondary Electron Microscopy (SEM). These materials showed good ferroelectric and ferromagnetic properties (>10 %) at room temperature. Room temperature multiferroicity were observed in PZTFT for x > 10%. PZTFT illustrated high dielectric constant and low loss at room temperature. The dielectric maximum temperature shifted to lower temperature side with increase in iron and tantalum concentration. For x = 0.30 it showed two consecutive phase transition, first transition indicates ferroelectric relaxor nature of the materials where as later one may be due to space charge similar to that of BaTiO3. Magnetization vs. applied magnetic field (M-H) curves showed well defined hysteresis with ramanent magnetization (~ 0.004- 0.13 emu/gm) and very small coercive field (900 Oe). Preliminary results indicate that PZFT is a promising candidate of room temperature multiferroic materials. AC and DC conductivity of PZTFT showed very low conductivity ~ 10-9 to 10-7 S/cm-1 at room temperature.
6:00 PM - I3.15
Nanoscale Polar Properties of Low-doped Manganates.
A. Kholkin 1 , R. Mamin 2 , I. Bdikin 1 , V. Amaral 3
1 Dept. of Ceramic and Glass Engineering & CICECO, University of Aveiro, Aveiro Portugal, 2 , Zavoisky Physical-Technical Institute of RAS, Kazan Russian Federation, 3 Dept. of Physics, University of Aveiro, Aveiro Portugal
Show AbstractComplicated interplay among charge, spin and lattice degrees of freedom in manganites is believed to induce peculiar magnetic and transport phenomena, such as the colossal magnetoresistance (CMR), which is one of the most notable phenomena in solid-state physics since the discovery of the high-temperature superconductivity. While the tendency to the inherent phase and charge segregation is widely discussed for both - manganites and high-temperature superconductors, clearly the microscopic origin of this extraordinary behavior is far from being understood and the question about the possibility and temperature region of the existence of these phenomena remains to be clarified. In manganites the metallic clusters start to form and their percolation may lead to the long-range charge order (LRCO) as well as to the CMR effect. In low-doped manganites the percolation is never complete and the characteristic temperature T* for the appearance of LRCO can be above the room temperature. In this presentation we will show that the tendency for the formation of the persistent polar areas with the increased charge concentration can appear in manganites already at room temperature. We report the direct evidence of the possibility of charge segregation in manganites via Scanning Probe Microscopy. The high contrast of electric-field-induced local charge states in (La,Sr)MnO3 is observed during more than 100 hours at room temperature. These induced states display clear piezoelectric response and locally induced polar properties. This effect allows creating a new multiferroic composite combining piezoelectric and ferromagnetic properties.
6:00 PM - I3.17
Microstructure Analysis and Multiferroic Properties of La0.67Sr0.33MnO3/Ba0.7Sr0.3TiO3 Superlattices Grown on (001) MgO.
Ricardo Martinez 1 , Shojan Pullockaran 1 , Raniel Calsada 1 , Ratnakar Palai 1 , Ram S Katiyar 1
1 Department of Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractThe crystallographic structures of La0.67Sr0.33MnO3/Ba0.7Sr0.3TiO3 (LSMO/BST) superlattices composed of ultrathin layers, grown on (001) MgO by pulsed laser deposition, are characterized by (XRD), (AFM) and Raman Spectroscopy. Ferroelectric properties and conductivity are measured as a function of temperature, frequency and electric field for different thickness. Magnetic properties as function of magnetic field and temperature are analyzed. We establish that both materials can keep their properties inside the heterostructure, which display a great potential within multiferroic applications.Keywords: ferroelectrics, manganites, superlattices, heterostructures, and multiferroic materials.
6:00 PM - I3.18
Domain Configuration and Switching Dynamics of Epitaxial BiFeO3 Thin Film using Angle-resolved Three-dimension Piezoelectric Force Microscopy.
Moonkyu Park 1 2 , Seungbum Hong 2 , Jeffrey A Klug 2 4 , Michael J. Bedzyk 4 5 , Orlando Auciello 2 3 , Kwangsoo No 1
1 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of), 2 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 4 Physics Department, Northwestern University, Evanston, Illinois, United States, 5 Materials Science Department, Northwestern University, Evanston, Illinois, United States, 3 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractWe present the domain configuration and polarization switching in the epitaxial BiFeO3 (BFO) thin film using angle-resolved three-dimension piezoelectric force microscopy (PFM). We fabricated 120 nm thick BiFeO3 thin films on 125 nm thick SrRuO3 (SRO) / (001) oriented SrTiO3 (STO) single crystal substrate using rf magnetron sputtering method. The out-of-plane and in-plane X-ray diffraction (XRD) measurements showed (001)c orientated epitaxial growth of both the BFO and the SRO layers on the STO substrate without any significant in-plane tilts or rotations of the BFO thin film grains.To calibrate the phase and amplitude signals of PFM, we used the (100) oriented BaTiO3 single crystal (MTI) as a reference sample and measured both the vertical and lateral phase and amplitude signals while rotating the sample from 0o to 180 o with an interval of 30o between each domain image. Subsequently, we conducted the same PFM experiments on the BFO films. We identified four additional polarization variants, which do not belong to the conventional {111} variants, in the annealed BFO thin films. We plan to conduct domain switching experiments using PFM and find the role of those newly found variants in the polarization reversals.
6:00 PM - I3.19
Crystal Structure and Orbital re-ordering ~ 1000K in Magnetoelectric Multiferroic TbMnO3.
Shishir Ray 1 , Mark Williamsen 1 , Ying Zou 1 , Somaditya Sen 1 , Adam Guenther 1 , Marshall Onellion 2 , Prasenjit Guptasarma 1
1 Physics Department, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, United States, 2 Physics Department, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractCo-existence of magnetic and ferroelectric order in the same crystalline phase in (RE)MnO3 (RE represents a Rare Earth Atom) has drawn significant recent attention. Ferroelectric order below 28K in TbMnO3 has been found to co-exist with antiferromagnetism: Mn3+ orders ~ 41K, and Tb3+ orders ~ 7K [1]. It is believed that a Dzyaloshinskii-Moriya (D-M) type interaction might be responsible for magnetoelectricity in this phase. The picture for TbMnO3 is not clear yet, but Jahn-Teller (JT) distorted Mn3+O6 octahedra are known to have a significant effect on the magnetic as well as electronic properties in LaMnO3 and other CMR perovskite systems [2]. Here, we explore the effect of elevated temperature (300-1300K) on the crystal lattice and electronic structure of TbMnO3. High temperature studies were performed on TbMnO3 single crystals as well as phase pure polycrystalline powder samples using a variable-temperature (300-1300K) SCINTAG 2000 diffractometer. Rietveld refinement indicates a structural distortion, resembling an orbital order-disorder transition, at ~1000K. Thermo-gravimetric (TG) studies in oxygen and inert atmosphere show a feature at the same temperature, pointing towards possible oxygen disorder induced distortion of MnO6 octahedra. We also report x-ray photoemission spectroscopy (XPS) studies in the same high temperature range, performed at the HERMON beamline (Port 33) of the Synchrotron Radiation Center (SRC) in Stoughton, WI using a home-made UHV compatible high temperature stage mounted on a two-pass cylindrical mirror analyzer from Physical Electronics, MN. The XPS measurements were performed on a high-quality single crystal grown from a floating zone in an two-mirror image furnace from NEC, Japan. Core and valence level XPS reveal changes in peak shape and peak width across the structural distortion temperature. Above this temperature, we find that Mn-3p and the Tb-4d peaks are clearly split, indicating a lifting of degeneracy in these orbitals. This could be caused by a high temperature Jahn-Teller (JT) distortion, or a charge ordering (CO) arising from charge disproportionation of Mn3+ to Mn2+ and Mn4+[3]. We note that the observed energy split of ~10 eV is somewhat too large for a typical JT energy split. High temperature resistivity measurements reveal an insulator to metal like transition at ~1000K, further supporting a CO mechanism.1.Pimenov A et al, NATURE PHYSICS 2, 97 (2006)2.Zhou JS, Goodenough JB, Phys. Rev. Lett. 96, 247202 (2006) 3.Mazin I.I et al, Phys. Rev. Lett. 98, 176406 (2007)
6:00 PM - I3.2
A Tunable Multiferroic Antenna.
Roman Petrov 1 , Gopalan Srinivasan 1 , Mirza Bichurin 2 , A. Filippov 2
1 Physics, Oakland University, Rochester, Michigan, United States, 2 Institute of Electronic and Information systems, Novgorod State University, Veliky Novgorod Russian Federation
Show AbstractMagneto-dielectric composites with high permeability and permittivity are of interest for antenna miniaturization [1]. Here we discuss the design and characterization of tunable microwave antennas with ferrites mounted on a dielectric substrate. The patch antenna consisted of a 4x4 cm2 dielectric substrate on which ferrites were placed. We used two kinds of ferrites: single crystal yttrium iron garnet films (4πMs=1750 G ΔH ≤ 1 Oe) or polycrystalline ferrite cubes (4πMs=200 G, ΔH ≤ 40 Oe). The antenna showed resonance at frequency 2 GHz for a bias field of 260 Oe for the film and 790 Oe for the cubes. The antenna operating frequency could be tuned by 0.1 MHz for 1 Oe of variation in the bias magnetic field. The antenna gain factor was 8 dB. The dielectric could possibly be replaced by a low-loss ferroelectric for further miniaturization.[1]. “Antenna miniaturization with ferrite-ferroelectric composites,” R. Petrov, A. Tatarenko, G. Srinivasan, and J. V. Mantese, Mic. Opt. Tech. Lett. 50, 3154 (2008).
6:00 PM - I3.20
Evidence of Magnetoelectric Coupling in Pb(Fe0.5Nb0.5)O3 Ceramics Through Impedance Spectroscopy and Electromechanical Resonance Measurements.
Oscar Raymond 1 , Reynaldo Font 2 , Jorge Portelles 2 , Nelson Suarez Almodovar 2 , Jesus Siqueiros 1
1 Centro de Nanocencias y Nanotecnología, Universidad Nacional Autónoma de México, San Ysidro, California, United States, 2 Facultad de Física-IMRE, Universidad de La Habana, La Habana Cuba
Show AbstractMultifunctional materials such as the single phase compound Pb(Fe0.5Nb0.5)O3 (PFN), where ferroelectric and antiferromagnetic order coexist, are very promising and have great interest from the academic and technological points of view. In this work, coupling of the ferroelectric and magnetic ordering have been observed. For this study, a combination of the small signal response using impedance spectroscopy and the electromechanical resonance method with the large signal response through standard ferroelectric measurements has been used with and without an applied external magnetic field. Measurements to determine the electrical properties of the ceramic were performed as functions of the bias and poling electric fields. A simultaneous analysis of the complex dielectric constant ε , impedance Z, electric modulus M , admittance Y , and the electromechanical coupling factors is presented. The results are correlated with a previous study of structural, morphological, small signal dielectric frequency-temperature response, and the ferroelectric hysteretic, magnetic and magnetodielectric behaviors.1-4 The observed shift of the resonance and antiresonance frequency values can be associated with changes of the domain size favored by the readjustment of the oxygen octahedron when the magnetic field is applied.1 O. Raymond et al, J. Appl. Phys. 97, 084107 (2005).2 O. Raymond et al. J. Appl. Phys. 97, 084108 (2005).3 O. Raymond et al. J. Appl. Phys. 99, 124101 (2006).4 R. Font et al. Appl. Phys. Letters 93, 172902 (2008).This work was partially supported by DGAPA-UNAM (Projects IN109608 and IN102908) and CoNaCyT (Projects Nos. 49986-F and 82503). The authors thank E. Aparicio, P. Casillas, J. Peralta, J. Hernández, A. Tiznado, and E. Medina for their technical assistance.
6:00 PM - I3.22
Ultraviolet Photoresponse of ZnO-based Polycrystalline Thin Film by Inkjet Printing.
Yan Wu 1 , Takahiko Tamaki 1 , Wolfgang Voit 1 , Lyubov Belova 1 , K. Rao 1
1 Dept. of Materials Science, Royal Institute of Technology, Stockholm, Stockholm lan, Sweden
Show Abstract Electrical and photoelectrical properties of undoped and Al- doped(2%) zinc oxide films deposited on glass by ‘in-situ’ inkjet printing technique have been investigated at room temperature in various ambient atmospheres. The polycrystalline hexagonal 120 to 300 nm thin films are randomly oriented with the average grain size of around 20 nm. The dark conductivity of the doped films exponentially decreases by about one order of magnitude in comparison with that of undoped zinc oxide film. Also, the conductivity of undoped and doped films decreases by about one order of magnitude when illuminated by UV light. Such sensitivity to UV light increases with decreasing film thickness. A study of the effects of film thickness, and the time dependence of the resistance after UV irradiation have also been carried out. Consequently thinner films with conductivity about 2.4×10-3 (Ohm×cm)-1 showed larger photoresponse than thicker films. The observed film thickness dependence is explained in terms of the variation of the grain size with the film thickness, and surface oxygen state as well as the additional effect of the Schottky barrier generated between the film and silver electrodes. ‘In-situ’ ink-jet printing of electronic components is versatile and cost-efficient method of producing electronic components for transparent electronics of the future.* This research is supported by the Swedish Agency VINNOVA, Swedish Research Council and the Hero-M Center of Excellence at KTH. Yan Wu acknowledges a graduate scholarship under the Chinese Scholarship Council-KTH program
6:00 PM - I3.3
A Ferrite-ferroelectric Electrically Tunable Microwave Phase Shifter.
Mirza Bichurin 2 , Alexander Tatarenko 1 2 , Gopalan Srinivasan 1
2 Institute of Electronic and Information Systems, Novgorod State University, Veliky Novgorod Russian Federation, 1 Physics, Oakland University, Rochester, Michigan, United States
Show AbstractAn electrically tunable phase shifter based on layered ferrite-ferroelectric structure is reported. The electrical control of the phase shift is realized through microwave magnetoelectric (ME) effects. A trilayer structure consisting of lead magnesium niobate-lead titanate (PMN-PT) and yttrium iron garnet (YIG) film on gadolinium gallium garnet (GGG) substrate is placed on a microstrip transmission line on an alumina substrate. The (111) YIG film of thickness 27 µm thick and 4 mm diameter was bonded to a poled (001) PMN-PT. The ME resonator is placed in an area of circular polarization of the microwave magnetic field, and a bias field H slightly above the ferromagnetic resonance (FMR) field is applied parallel to the sample plane. Electrical tuning of the phase shift is realized with the application of a voltage to PMN-PT. The piezoelectric deformation is transmitted to YIG, leading to a frequency shift in FMR and the phase of the signal. For reduction of losses the operating frequency is shifted away from FMR. Experimental results showed 40 deg. differential phase shift for electric field E=0-10 kV/cm in the frequency range 6 - 9 GHz.
6:00 PM - I3.4
Magnetoelectric Gradiometer.
Yuri Pukinski 1 , Mirza Bichurin 1 , Sergey Ivanov 1 , Rashed Islam 2 , Vishwas Bedecar 2 , Shashank Priya 2
1 , Novgorod State Univetrsity, Veliky Novgorod Russian Federation, 2 , Virginia Tech., Blacksburg, Virginia, United States
Show AbstractGradiometer is a magnetic field sensor that measures the magnetic field gradient at a specific distance or at specific interval of time. In this study, we investigate two designs of magnetoelectric (ME) gradiometer based upon ME composites. The structure of gradiometer utilizes ring-dot electrode pattern similar to that in trilayer unipoled piezoelectric transformers working near resonance. In first design, the gradiometer had ring-dot electrode pattern printed on top surface of PZT, where ring acts as the input while dot acts as the output. The output section had a diameter of 15 mm and the input section had a width of 5 mm. There was a 2 mm insulation gap between the input and output section. Magnetostrictive disc with diameter of 13 mm was bonded on top of the output section, resembling a bilayer composite structure. In the second design, the gradiometer had two layered magnetostrictive electrodes (input and output) and interlayer of PZT. The length of the sample was 14 mm with width of 2 mm. There was a 1mm insulation gap between input and output section. Further, we characterize the performance of ME gradiometers based upon two different sets of composite materials: (i) Terfenol–D – PZT and (ii) Ni – PZT. Measurements were performed as a function of frequency (in the range of 70-120 kHz) and dc magnetic field range (in the range of 0-3000Oe) for an applied AC magnetic field. The resonance frequency of the sample was found to be in the range of 91 – 94 kHz. The working principle of gradiometer can be explained as following: The generated magnetic field due to converse ME effect interacts with the externally applied magnetic field producing flux gradient which is detected through the frequency shift and output voltage change. The results illustrate the promising nature of our design.
6:00 PM - I3.5
Modeling of Magneto-acoustic Resonance in Ferrite-piezoelectric Structures.
Mirza Bichurin 2 , Gopalan Srinivasan 1 , Vladimir Petrov 2 , A. Filippov 2
2 Institute for Electronic Information Systems, Novgorod State University, Veliky Novgorod Russian Federation, 1 Physics, Oakland University, Rochester, Michigan, United States
Show AbstractComposites of ferromagnetic and piezoelectric phases reveal the giant magnetoelectric (ME) effects that is facilitated by the sample response to electric, magnetic, and elastic forces. ME interaction becomes stronger in such materials when the magnetic and/or electric subsystems show resonance behavior. Two types of resonances are of importance: electromechanical resonance (EMR) for the piezoelectric component and ferromagnetic resonance (FMR) for the magnetic phase. Further increase in ME effect strength occurs at the coincidence of EMR and FMR, i.e., at the magneto-acoustic resonance (MAR). At that, the highest EMR frequency is determined by thickness of the sample and the lowest FMR frequency is connected with saturation magnetization of the magnetic phase.The primary task of this study is to establish the correlation of sample geometry and frequency regions where the observation of MAR is possible. Our theoretical model rests on the equation of media motion, equation of motion of magnetization, law of elasticity, constitutive and electrostatics equations. As an example, bilayers of yttrium iron garnet (YIG) and lead zirconate titanate (PZT) or lead magnesium niobate-lead titanate (PMN-PT) are investigated. The results of our research indicate that the lowest usable frequency for observation of MAR in the bilayer of YIG and PMN-PT approximately equals 1 GHz. That is bound up with the requirement that bias field should be high enough to drive the ferrite to a saturated (single domain) state. When domains are absent, magnetic losses are minima. Calculation shows that at MAR frequency of 1 GHz the YIG and PMN-PT film thickness equal 0.2 and 0.1 μm, correspondingly. The highest MAR frequency possible is determined by EMR frequency dependence on thickness of the sample.The obtained expressions for ME coefficient enable determining the microwave ME susceptibility and can be used at developing the new type of devices.
6:00 PM - I3.6
Magnetoelectric Microwave Gyrator.
Andrey Filippov 1 , Mirza Bichurin 1 , Roman Petrov 1 , Edward Liverts 2
1 Design and Technology of Radioequipment, Novgorod State University, Veliky Novgorod, Novgorod region, Russian Federation, 2 Mechanical Engineering, Ben-Gurion University of the Negev, Beersheva Israel
Show AbstractThe magnetoelectric (ME) gyrator is a device allowing to convert both active and reactive impedances, to shift electromagnetic wave phase on 180 deg. and to transform current into voltage. Here we discuss the original structure of microwave ME gyrator consisted of dielectric substrate with inductive and capacitor microstrip electrodes and ME element based on trilayer structure of gadolinium gallium garnet, yttrium iron garnet and lead zirconate titanate. Our structure works more effective at magnetoacoustic resonance (MAR) in the microwave region. It is necessary to carry out the coincidence of ferromagnetic and electromechanical resonance frequencies for MAR. Estimations show that we will get the increase of ME interaction at MAR that will allow to perform all functions of the impedance converter in the microwave range. This device represents considerable interest for designers of complex electronic microwave schemes.
6:00 PM - I3.7
Dual Magnetic Field and Mechanical Vibrations Energy Harvesting System.
Mirza Bichurin 1 , Vladimir Petrov 1 , Shuxiang Dong 2 , Xiaoxi Cui 2 , Junyi Zhai 3 , Jie-Fang Li 3 , Dwight Viehland 3 , Shashank Priya 3
1 Design and Technology of Radioequipment, Novgorod State University, Veliky Novgorod, Novgorod region, Russian Federation, 2 College of Engineering, Peking University, Beijing China, 3 Materials Science and Engineering, Virginia Tech., Blacksburg, Virginia, United States
Show AbstractRecently synthesized magnetostrictive/piezoelectric 2-1 composites exhibit giant response to magnetic, and elastic energy inputs. As an example, the trilayer structure based on lead zirconate titanate and Terfenol-D plates was considered. In this study we report a theoretical model for multimodal energy harvesting system that simultaneously takes magnetic field energy and mechanical energy as inputs and converts them into electricity.1 The conversion mechanism utilizes a magnetostrictive/piezoelectric layered composite structure. Theoretical analysis is based on elastodynamics, electrostatics and magnetostatics equations. The output electric energy is assumed to consist of combined magnetoelectric and piezoelectric contributions. Our model enables determining the necessary operating conditions for achieving the maximum output electric energy. The variation of power level with mechanical vibration and magnetic field oscillation phases was calculated. The estimated variation of output power density with resistive load presented in this manuscript can be used for obtaining the optimum magnitude of external load. The influence of bias field amplitude and magnetic field direction on efficiency was also studied. Numerical estimations were determined for various cases combining the contribution towards generated electricity through piezoelectric and magnetoelectric components in different arrangements. The results of this study illustrate a promising concept for development of the multimodal energy harvesting system. 1. S. Dong, J. Zhai, J.F. Li, D. Viehland and S. Priya, Appl. Phys. Lett., 93, 103511 (2008).
6:00 PM - I3.8
Magnetic Resonance in Ferrite/piezoelectric Nanobilayer.
Mirza Bichurin 1 , Vladimir Petrov 1 , Edward Liverts 2
1 Design and Technology of Radioequipment, Novgorod State University, Veliky Novgorod, Novgorod region, Russian Federation, 2 Mechanical Engineering, Ben-Gurion University of the Negev, Beersheva Israel
Show AbstractMechanical deformation in a ferromagnetic-ferroelectric heterostructure results in the magnetoelectric (ME) effect. Mechanical stresses arising in the magnetic phase due to magnetostriction in applied magnetic field are transferred to the piezoelectric phase, where they produce an electric polarization due to piezoelectric effect. Microwave ME interactions in ferrite-piezoelectric bilayers consists in the shift of ferromagnetic resonance (FMR) line that is stipulated by inducing an additional uniaxial anisotropy. This anisotropy is connected with an electric field produced mechanical deformation in the ferroelectric that is transferred to the ferrite phase. Data on this shift as a function of applied electric field enable one to obtain information on the nature of ME coupling. The particular purpose of present investigation is ME interactions at microwave frequencies (9-10 GHz) in single crystal bilayers of ferrite and ferroelectrics. In contrast to well-known theory, our theoretical approach enables to take into account the contribution of flexural strain to ME effect in the layered systems. For this case, a strong ME interaction is expected based on results of recent investigations on the ME effects at bending modes in layered structures. In addition, we estimate the clamping effect of substrate. Expressions have been obtained for magnetic resonance field shift using simultaneous solution of motion equation of magnetization for ferrite and electrostatics equations. The proposed theory is applied to specific cases of a bilayer of yttrium iron garnet (YIG) and lead magnesium niobate-lead titanate (PMN-PT) YIG/PMN-PT. Epitaxial YIG film is assumed to be on a gadolinium gallium garnet substrate and the PMN-PT plate is bonded to YIG film. The strength of ME interaction for a free standing bilayer is predicted to decrease because of bending the sample. At the same time, placing the bilayer on a substrate leads to a decrease in substrate clamping effect. As a result, rate of decrease in ME coupling strength is considerably lower than that for the case when neglecting the flexural strains.
6:00 PM - I3.9
Magnetic Anisotropy of Artificial Multiferroic Fe layer/BaTiO3 Heterostructure.
Tomoyasu Taniyama 1 2 , Kyohei Akasaka 1 , Desheng Fu 1 , Mitsuru Itoh 1
1 Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama Japan, 2 PRESTO, Japan Science and Technology Agency, Tokyo Japan
Show AbstractMultiferroic materials have attracted much attention due to mutual control of magnetization and electric polarization by electric field and magnetic field, respectively. In particular, electric-field control of magnetic anisotropy in artificial multiferroic heterostuctures such as Fe/BaTiO3 is the central issue for developing spintronic devices. In order to achieve the electric control, the effect of interfacial strain on the magnetic anisotropy of the ferromagnetic Fe layer is of critically importance. In this report, we study strain-induced magnetic anisotropy in the Fe layer of an epitaxially grown Fe/BaTiO3 heterostructure, where the structural phase transition of BaTiO3 efficiently transfers strain to the Fe layer at the transition temperature. We clearly observe a significant change in the magnetic anisotropy when the structural phase transition of the ferroelectric aTiO3 occurs at 282 K and 186 K. 30-nm-thick Fe layers were grown on BaTiO3 (BTO) (001) single crystal substrates using ultrahigh vacuum molecular beam epitaxy at room temperature. Since the a-axis lattice spacing of BTO is 3.99 Å in the tetragonal phase at room temperature, Fe having a lattice constant of 2.87 Å can be grown epitaxially on BTO with a lattice mismatch of 1.4% when the principal axis is rotated by an angle of 45° to each other, i.e., Fe [110] is parallel to BTO [100]. Magnetization of Fe layers was measured in a superconducting quantum interference device (SQUID) magnetometer at temperatures between 300 K and 150 K. The in-plane magnetization exhibits a sudden drop at T1=282 K by a factor of 0.38 and again increases up to the almost initial value at T2=186 K with decreasing temperature. The temperatures showing these magnetization jumps clearly correspond to the successive structural phase transitions of BTO from tetragonal to orthorhombic and from orthorhombic to rhombohedral structures, respectively, and the significant change in the magnetization is due to a variation in the magnetic anisotropy of the Fe layer originating from the lattice strain at the Fe/BTO interface associated with the phase transition of BTO. The sign of the change in the magnetization indicates that tensile stress occurs at T1 while compressive stress occurs at T2 considering the negative magnetostriction constant of Fe along <110>. Also, the in-plane magnetization at 223 K and 298 K, where BTO is in the orthorhombic phase and tetragonal phase, respectively, clearly shows a variation in the magnetization curves, depending on the crystal structure of the BTO substrate. The results are compatible with the description that the strain at the Fe/BTO interface modifies the magnetic anisotropy of Fe due to the magnetostriction effect. Therefore, we conclude that the artificial multiferroic Fe/BaTiO3 heterostructure is one of the most promising candidates for controlling the magnetization orientation through magnetoelectric effect under the application of electric voltage.
Symposium Organizers
Gopalan Srinivasan Oakland University
Mirza I. Bichurin Novgorod State University
Shashank Priya Virginia Tech
Nian X. Sun Northeastern University
I6: Multiferroic Bismuth Iron Oxide
Session Chairs
Thursday AM, April 16, 2009
Room 2012 (Moscone West)
9:30 AM - **I6.1
Electric-Field-Driven Conductor-Insulator Transition in Doped Multiferroic.
Chan-Ho Yang 1 , Jan Seidel 1 2 , Sang-Yong Kim 3 , Pim Rossen 3 , Pu Yu 1 , Ying-Hao Chu 4 , Martin Gajek 1 , Nina Balke 3 , Micky Holcomn 1 2 , Lane Martin 2 3 , Sourav Basu 3 , Matt Scullin 3 , R. Ramesh 1 2 3
1 Physics, University of California, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Material Science and Engineering, University of California, Berkeley, California, United States, 4 Material Science and Engineering, National Chiao Tung University, HsinChu Taiwan
Show AbstractCompetition between multiple ground states, that are energetically similar, plays a key role in many interesting material properties and physical phenomena as for example in high-Tc superconductors (electron kinetic energy vs. electron-electron repulsion), colossal magnetoresistance (metallic state vs. charge ordered insulating state), and magnetically frustrated systems (spin-spin interactions). Here we address a new concept of competing phenomena in doped multiferroics – an electronic conductor-insulator transition by control of band-filling. It is exploited by application of electric field which sweeps oxygen vacancies and varies hole carrier concentration. In this talk, we present systematic investigations of divalent Ca doping of ferroelectric BiFeO3 and we establish the phase diagram for varying doping concentration and temperature. A ferroelectric – paraelectric phase boundary is found around a Ca concentration of ~ 1/8, where a new pseudo-tetragonal phase appears. We show that electronic conduction can be enhanced and modulated by applying electric fields above a certain threshold voltage. The conductivity reversibly returns to the original insulating state by applying the opposite electric field. Possible mechanisms for the observation are discussed based on the interplay of ionic and electronic conduction. This work was supported by the US Department of Energy.
10:00 AM - **I6.2
Microstructure and Local Ferroelectricity in BiFeO3–based Thin Films.
R. Ranjith 1 , Ph Boullay 1 , U. Lüders 1 , Wilfrid Prellier 1 , A. Da Costa 2 , I. Dupont 2 , R. Desfeux 2
1 CNRS/ENSICAEN, Laboratoire CRISMAT, Caen France, 2 UCCS, Université d’Artois, Lens France
Show AbstractFerroelectric BiFeO3 thin films and artificial superlattices of (BiFeO3)m(SrTiO3)m (m=1 to 10 unit cells) were grown on (001)-oriented SrTiO3 substrates by pulsed laser ablation. First, the variation of leakage current and macroscopic polarization with periodicity was performed. Second, a detailed microscopy study was undergone using transmission electron microscopy and near field microscopy. Electron diffraction study reveals that the BiFeO3 layers exhibit a distorted perovskite structure compatible with its bulk form while the two components can be evidenced at the film/substrate interface. The mismatch between the first deposit BiFeO3 layers and the substrate seems accommodated trough the formation of an approx. 1.2nm thick interface indicating a good quality of the layers. Piezo force microscopy studies indicate the presence of large ferroelectric domains in the case of BiFeO3 thin films while a size reduction in ferroelectric domains was observed in the case of superlattice structures. Finally, we will show that the modification of ferroelectric domains through superlattice, provide an opportunity to alter the polarization, the leakage current and also facilitates modifying the domain size, pattern and coercive voltages, which are known to directly influence on the multiferroic coupling in the case of multiferroic BiFeO3 thin films and its applications. This work was carried out in the frame of the STREP MaCoMuFi (NMP3-CT-2006-033221) supported by the European Community and by the CNRS, France. Partial support from the Région Basse Normandie thought the CPER and the C-Nano program is also acknowledged.
10:30 AM - **I6.3
Tailoring of Structure and Properties in Bismuth Ferrite Thin Films and Ceramics.
Ashish Garg 1 2
1 Materials and Metallurgical Engineering, Indian Institute of Technology Kanpur, Kanpur, UP, India, 2 School of Applied Sciences, RMIT University, Melbourne, Victoria, Australia
Show AbstractBismuth ferrite (BiFeO3 or BFO) has been a subject of intense research for past few years primarily because of its potential for many applications due to co-existence of ferroelectric and magnetic ordering in the same phase. We have conducted systematic studies on altering the properties of bismuth ferrite thin films and ceramics by doping as well as by making solid solutions with isomorphic compound, PbTiO3. We have found that there are subtle structural variations in the properties of BFO depending upon the substituting element. These structural changes are accompanied by change in the properties, both electrical and magnetic. Extent of modification in the properties depends upon of the level of substitution and the processing conditions. For example lanthanum doped samples show that material tends to adopt a structure which is more symmetric than parent rhombohedral structure. Zr-doped samples also show structural distortions and large insulation resistance as shown by low leakage. However, the compounds tend to loose the ferroelectric nature as the Zr content increases. Sample prepared in solid solution with PbTiO3 showed structural changes away from the equilibrium structures and displayed room temperature ferroelectricity. Although, some of the above samples show finite magnetization, role of parasitic phases is not ruled out.
11:00 AM - I6: Bismuth
BREAK
11:30 AM - **I6.4
Crystalline and Ferroelectric Properties of BiFeO3 Thin Films Deformed by Stress from Substrate and Electric Field.
Masanori Okuyama 1 , Seiji Nakashima 1
1 Dept. of Systems Innovation, Grad. School of Eng. Sci., Osaka University, Toyonaka Japan
Show AbstractMultiferroics have attracted much attention as materials for application such as memory, sensors, actuators, and so on. Among them, perovskite BiFeO3 (BFO) is a leading candidate, which shows giant ferroelectric polarization (Pr ~ 152 _C/cm2) at 80K in thin film form. Crystalline and ferroelectric properties of the BFO thin film is strongly affected by the stress. However, details of crystal structure deformation induced by stresses from substrate and electric field have not been investigated enough. In this presentation, we have clarified the stress dependence of crystal structure of each (001)- and (110)-oriented crystal grains in the polycrystalline BFO thin films using reciprocal space mapping measurements, and also investigated the electric-field-induced strains of the each crystal grains by time-resolved x-ray diffraction using synchrotron radiation. 350-nm-thick (001)- and (110)-oriented polycrystalline BFO thin films were deposited on Pt /TiO2 /SiO2 /Si (625 μm) substrate by pulsed laser deposition (PLD). Moreover, the BFO thin films were also deposited on Pt /TiO2 /SiO2 /Si (15 μm) membrane structure for relaxing the stress from substrates. Reciprocal space mapping measurements indicated that the BFO thin film has tensile stress initially, and (001)- and (110)-oriented grains of BFO thin films have different crystal structure of Mc phase monoclinic and Mb phase monoclinic structure, respectively, due to the tensile stress. Moreover, the crystal structures become close to that of bulk BFO by relaxing the tensile stress from substrates. From ferroelectric P-E hysteresis measurements, remanent polarization was enhanced from 91 μC/cm2 to 96 μC/cm2 due to relaxing the stress. The time-resolved x-ray diffraction measurements under pulse electric fields were also performed for confirming crystal structure deformations by electric-field-induced strains. Electric field pulses of 804.09 ns period and 150 ns width synchronized with synchrotron radiation source were applied to the films. The diffraction peaks from BFO (001) and (110) planes shift to lower angle during electric field application. From these peak shifts, these electric-field-induced strains increase linearly as increasing amplitude of the pulse electric fields. Therefore, the crystal structure deformations are due to piezoelectric responses, and piezoelectric constants (d33) of (001)- and (110)-oriented grains are 27.8 pm/V and 26.4 pm/V, respectively. It is considered that these responses are intrinsic properties of each oriented grain of the polycrystalline BFO thin film.
12:00 PM - I6.5
Conductivity Distribution within Microstructurally Engineered BiFeO3 Ceramics.
Matjaz Valant 1 2 , Anna-Karin Axelsson 2 , Derek Sinclair 3 , Neil Alford 2
1 Laboratory for Electronic and Environmental Materials, University of Nova Gorica, Nova Gorica, 0, Slovenia, 2 Department of Materials, Imperial College London, London United Kingdom, 3 Department of Engineering Materials, University of Sheffield, London United Kingdom
Show AbstractAs a model multiferroic material BiFeO3 exhibits few unfavorable properties, among which a high leakage current is one of the most detrimental for an application in electronic devices. This problem was realized already in an early stage of recent interest in multiferroics but only few researchers have systematically investigated the origin of the increased conductivity in pure BiFeO3 ceramics. The reasons for this may be found in difficulties to produce single phase BiFeO3 ceramics and in the fact that the leakage current can be successfully suppressed with doping. The large leakage current is often referred as being caused by charge defects, oxygen vacancies, non-stoichiometry and secondary phases. The large leakage current increases the dielectric loss and makes it difficult to obtain a well-saturated ferroelectric hysteresis loop. Therefore, it prevents BiFeO3 to be used in practical device applications. However, no systematic study of the leakage mechanism in BiFeO3 ceramics has ever provided any consistence evidence of the different mechanism of the conductivity in bulk BiFeO3. We show that a successful synthesis of a single phase BiFeO3 powder essentially depends on a purity of starting materials.1 The impurities cause the Bi2O3-Fe¬2O3 system to shift in a quasi-ternary system and a nominal composition to move into a phase field with sillenite and Bi2Fe4O9 phases. With respect to the nature of the impurities, variations in an amount of the secondary phases occur and microstructural characteristics significantly change. By understanding these relationships we were able to engineer the microstructure of BiFeO3. We synthesized BiFeO3 ceramics with representative microstructures to investigate the electric characteristics of bulk and grain boundaries as a function of the microstructural characteristics. Using impedance spectroscopy we managed to determine bulk and grain boundary contribution to the conductivity and identify the main sources of the increased leakage current.
12:15 PM - I6.6
Controlling Magnetism in Multiferroic BiFeO3 Thin Films.
Mikel Holcomb 1
1 , University of California, Berkeley, Berkeley, California, United States
Show AbstractBiFeO3 (BFO) has attracted a great deal of recent attention due to the fact that it is the only single phase room temperature magnetoelectric multiferroic currently known. Not only does it have applications as a lead-free replacement for ferroelectric memory cells and piezoelectric sensors, but its interactions with other materials are now attracting a great deal of attention. Its multiferroic nature has potential in the field of exchange bias, where it could allow electric-field control of the ferromagnetic (FM) magnetization. In order to understand this coupling, an understanding of the magnetization in BiFeO3 is necessary. Angle and temperature dependent x-ray absorption measurements allow decoupling of the two order parameters, ferroelectric and magnetic, contributing to BFO's dichroic signal. Careful comparison with models of linear spectra allow determination of magnetic directions in BiFeO3 films of different thicknesses and reveal the ability to control a preferred antiferromagnetic axis both electrically and through strain.
I7: Single Phase Multiferroics
Session Chairs
Thursday PM, April 16, 2009
Room 2012 (Moscone West)
2:30 PM - **I7.1
Epitaxially Strained TbMnO3 Films.
Christophe Daumont 1 , Diego Rubi 1 , Coen de Graaf 2 , Dan Mannix 3 , Ria Broer 1 , Beatriz Noheda 1
1 Zernike Institute for Advanced Materials, University of Groningen, Groningen Netherlands, 2 , Institucio Catalana de Recerca i Estudis Avancats (ICREA), , Barcelona Spain, 3 , Institut Neel, CNRS-UJF, Grenoble France
Show AbstractFor practical devices, multiferroics are preferred in thin film form. Moreover, the strain induced by the mismatch between the film and the substrate lattice parameters brings an additional parameter and can lead to different materials properties that those of the bulk. Interestingly, although TbMnO3 is by now a well known material, only a few reports of this perovskite in thin film form are available. When growing thin films of perovskites, SrTiO3 is often the first choice as a substrate, due to the atomically-flat surface that can be attained in the (001) orientation, which allow growing the films with high crystalline quality. In this work, epitaxial TbMnO3 films have been grown under compressive strain on (001)-oriented SrTiO3 crystals. The films have an orthorhombic structure and display the (001) orientation. Those with thickness below about 70 nm are coherent with the substrate along one of the <100> in-plane directions. With increasing thickness, the structure evolves from a less distorted (more squared) to a more distorted (bulk-like) in-plane lattice, keeping the strain state and, thus the out-of-plane lattice spacing, unchanged. This unusual strain modification leads to remarkable changes in the magnetic properties and, unlike the bulk material, the films display ferromagnetic interactions below the ordering temperature TN~40K. The magnetic anomaly related to the lock-in transition at T~28K is absent in the films. X-ray photoemission measurements in the films show that the splitting between the two Mn-3s peaks, which originates from the exchange coupling between the 3s hole and the 3d electrons, is 0.3 eV larger than that of the bulk. Ab initio embedded cluster calculations yield Mn-3s splittings that are in agreement with the experiment and reveal that the larger observed values are not due to changes in the Mn valence, as typically assumed, but due to changes in the nature of the Mn-O bonding. In particular, the compressive strain in the ab plane increases the ionicity of the films. The possible origins of the induced ferromagnetism in the films are discussed. Aside from the multiferroic character of the films (of which we have no evidence at the moment of writing this abstract), the capability of tuning the orthorhombic distortion with thickness is of more general interest, since the physical properties of manganites and other perovskites critically depend on this parameter.
3:00 PM - I7.2
Electrical Conduction at Domain Walls in Multiferroic BiFeO3.
Jan Seidel 1 2 , Lane Martin 2 3 , Qing He 1 , Qian Zhan 2 , Ying-Hao Chu 2 3 4 , Axel Rother 5 , Michael Hawkridge 2 , Peter Maksymovych 6 , Pu Yu 3 , Martin Gajek 1 , Nina Balke 3 , Sergei Kalinin 6 , Sybille Gemming 7 , Feng Wang 1 , Gustau Catalan 8 , James Scott 8 , Nicola Spaldin 9 , Joseph Orenstein 1 2 , Ramamoorthy Ramesh 1 2 3
1 Department of Physics, UC Berkeley, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Department of Materials Science and Engineering, UC Berkeley, Berkeley, California, United States, 4 Department of Materials Science and Engineering, National Chiao Tung University, Hsin Chu China, 5 Institute of Structure Physics, TU Dresden, Dresden Germany, 6 Center for Nanophase Materials Science, Oak Ridge National Laboratory, Hsin Chu, Tennessee, United States, 7 , Forschungszentrum Dresden-Rossendorf, Dresden Germany, 8 Department of Earth Sciences, University of Cambridge, Cambridge United Kingdom, 9 Materials Department, UC Santa Barbara, Santa Barbara, California, United States
Show AbstractWe report the observation of room temperature electronic conductivity at ferroelectric domain walls in BiFeO3. The origin and nature of the observed conductivity is probed using a combination of conductive atomic force microscopy, high resolution transmission electron microscopy and first-principles density functional computations. We show that a structurally driven change in both the electrostatic potential and local electronic structure (i.e., a decrease in band gap) at the domain wall leads to the observed electrical conductivity. We estimate the conductivity in the wall to be several orders of magnitude higher than for the bulk material. Additionally we demonstrate the potential for device applications of such conducting nanoscale features.This work is supported by the US DOE, ONR MURI, NSF Chemical Bonding Center program, and the Alexander von Humboldt Foundation.
3:15 PM - I7.3
Effect of Epitaxial Strain on Multiferroic Properties in BiFe1-xCrxO3 Epitaxial Films.
Dae Ho Kim 1 2 , Michael Biegalski 3 , Hans Christen 2 3
1 Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana, United States, 2 Materials Science and Technology Division, Oak Ridge Natioanl Laboratory, Oak Ridge, Tennessee, United States, 3 Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractEpitaxial strain has been extensively utilized to manipulate desired properties in broad range of materials. In multiferroics, where ferroicity (or antiferroicity) both in magnetism and dielectric polarization occur simultaneously, the role of epitaxial strain is even more important. Here we investigate the multiferroic properties under structural modification by epitaxial strain in thin films of BiFe1-xCrxO3. The contrast in ferroelectric properties and the similarity in structure make the choice of this materials system interesting. Note that BiFeO3 exhibits large polarization and antiferromagnetic properties whereas BiCrO3 exhibits antiferroelectricity and weak ferromagnetic moment parasitic to antiferromagnetic order.[1,2] By alternating ablation from BiFeO3 and BiCrO3 targets, we have successfully grown a series of BiFe1-xCrxO3 solid-solution epitaxial films on SrTiO3 substrates with various orientations. Robust ferroelectricity with the polarization along the body-diagonal of the pseudo-cubic has been observed in wide range of x. Systematic analysis with scanning probe microscopy together with temperature dependency of structural properties reveals the relation between the epitaxial strain and multiferroic properties in BiFe1-xCrxO3.Research sponsored by the Division of Materials Sciences and Engineering (DHK, HMC) and the Division of Scientific User Facilities (MDB), Office of Basic Energy Sciences, U.S. Department of Energy.[1] D. H. Kim et al., Appl. Phys. Lett. 92, 012911 (2008). [2] D. H. Kim et al., Appl. Phys. Lett. 89, 162904 (2006).
3:30 PM - I7.4
Room Temperature Ferromagnetism In Thin films of a New ‘Biferroic’ Amorphous YbCrO3.
V. Rao 1 , Sandeep Nagar 1 , Lyubov Belova 1 , Gustau Catalan 4 , James Scott 4 , A. Tyagi 3 , O. Jayakumar 3 , R. Shukla 3 , Yi-Sheng Liu 2 , Jinghua Guo 2
1 Dept. of Materials Science, Royal Institute of Technology, Stockholm, Stockholm lan, Sweden, 4 Department of Earth Sciences, University of Cambridge, Cambridge United Kingdom, 3 Chemistry Division, Bhabha Atomic Research Centre, Mumbai India, 2 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractSearch for novel multifunctional materials, especially multiferroics, which are ferromagnetic above room temperature and at the same time exhibit a ferroelectric behaviour much above room temperature is an active topic of extensive studies today. Ability to address an entity with an external field, laser beam, and also electric potential is a welcome challenge to develop multifunctional devices enabled by nanoscience. While most of the studies to date have been on various forms of Bi- and Ba based Ferrites, Rare earth chromites are a new class of materials which appear to show some promise. However in the powder and bulk form these materials are at best canted antiferromagnetics with the magnetic transition temperatures much below room temperature.In this presentation we show that thin films of YbCrO3 deposited by Pulsed Laser Deposition exhibit robust ferromagnetic properties above room temperature. It is indeed a welcome surprise and a challenge to understand the evolution of above room temperature ferromagnetism in such a thin film. The thin films are amorphous in contrast to the powder and bulk forms which are crystalline. The magnetic properties are those of a soft magnet with low coercivity. We present extensive investigations of the magnetic and ferroelectric properties, and spectroscopic studies using XPS and XAS techniques to understand the electronic states of the constituent atoms in this novel Chromite. While the amorphous films are ferromagnetic much above room temperature, we show that any observation of ferroelectric property in these films is an artifact of a leaky highly resistive material. This Project is supported by the Swedish Research Council, Swedish Funding Agency VINNOVA and the Hero-M Centre of Excellence at KTH. The Advanced Light Source at Berkeley is supported by the Director, Office of Science, Office of Basic Energy Sciences of the US Department of Energy under Contract number DE-AC02-05CH11231.
3:45 PM - I7: Single
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4:15 PM - I7.5
Competing Magnetic Interactions in Magnetoelectric YbMnO3.
Shishir Ray 1 , Ying Zou 1 , Mark Williamsen 1 , Somaditya Sen 1 , Lawrence Buroker 1 , Prasenjit Guptasarma 1
1 Physics Department, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, United States
Show AbstractIntrinsic magnetoelectrics are multiferroic compounds which display simultaneous ground states of magnetic and ferroelectric ordering in the same crystalline phase. Manganite oxides of the form (RE) MnO3 (RE = Rare Earth element), which exist in tetragonal and orthorhombic forms, are known to simultaneously exhibit magnetism and ferroelectricity [1]. These have recently attracted much attention from the research community due to possible applications in spintronics, switching, and as media with negative refractive index. YbMnO3 is a hexagonal compound known to show ferroelectricity below 990K, antiferromagnetic order of Mn3+ below TN~80K and Yb3+ order at lower temperature. Here, we seek to characterize and understand the mechanism of competing magnetically ordered phases of Yb3+ and Mn3+ in response to applied magnetic and electric field, and clarify certain new features in the magnetic phase diagram [2].We have grown high-quality single crystals of YbMnO3, and have constructed a detailed phase diagram from variable temperature (0.3 – 400 K) measurements of ac and dc magnetization, specific heat, dielectric spectroscopy, electrical resistance, and ultrasound velocity in variable magnetic field (0 – 9 T). We have also performed detailed structural Rietveld refinement of high resolution x-ray diffraction using a synchrotron x-ray source. Single crystals of magnetoelectric YbMnO3 were grown by us using a floating zone technique in an NEC two-mirror infrared image furnace traveling at a relatively low speed of ~ 1.1 mm/hr. Magnetization, specific heat, and dielectric measurements were carried out on a Physical Property Measurement System (PPMS) and a Magnetic Property Measurement System (MPMS) manufactured by Quantum Design. Specific heat measurement was performed using relaxation calorimetry in the temperature range of 0.4K to100K with external applied field along the c axis of the crystal. Dielectric measurements were performed using an Agilent E4980A precision LCR meter set up using a multifunction probe on the PPMS. Ultrasound velocity measurements were performed using a home-made spectrometer.Consistent with recent neutron diffraction and Mossbauer studies, and based on several new features in the magnetic phase diagram, we believe that we observe two ordering sites of Yb: Yb3+ (2a) via Yb-Yb, and Yb3+ (4b) via Yb-Mn interactions within the hexagonal YbMnO3 structure [3]. These are clearly observed as two separate peaks in specific heat measurements. We also report that, contrary to other reports, the magnetic moment of Yb does not become fully suppressed with external magnetic field, but rather directly transitions from the P63cm (A1) order into the P63cm (A2) order at low temperature. 1.Aken, Bas B. et al. nature materials 3 (2004) 1642.F. Yen et al, Journal of Materials Research 22, 2163 (2007)3.X. Fabrèges et al, arXiv:0809.5013v1 (2008)
4:30 PM - I7.6
Advanced Spectroscopy and LEEM Imaging Studies of Multiferroicity in Y Doped HoMnO3.
Relja Vasic 1 , Marc Ulrich 1 , Jack Rowe 1 , Gerald Lucovsky 1 , Jurek Sadowski 2 , Haidong Zhou 3 , James Brooks 3 , Christopher Wiebe 3 , Xavier Marti 4 , Joseph Fontcuberta 4 , Young Choi 5 , Sang-Wook Cheong 5
1 Physics Department, North Carolina State University/ARO, Raleigh, North Carolina, United States, 2 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States, 3 Physics Department, National High Magnetic Field Laboratory, Tallahassee, Florida, United States, 4 Departament de Materials Magnètics i Oxids Funcionals, Institut de Ciència de Materials de Barcelona (CSIC), Barcelona, Catalunya, Spain, 5 Department of Physics and Astronomy , The State University of New Jersey , Rutgers, New Jersey, United States
Show AbstractThere has been recent research interest in a number of magnetic ferroelectrics, including YMnO3, a hexagonal perovskite that is antiferromagnetic [Neél temperature (TN) between 70 and 130 K] and ferroelectric [Curie temperature (TC) between 570 and 990 K] in the ground state and perovskite BiFeO3 which is ferroelectric (TC ~ 1103 K) and antiferromagnetic (TN ~ 643 K), exhibiting weak magnetism at room temperature due to a residual moment from a canted spin structure. These systems can be understood by competition between local interactions on several ion sites. We report synchrotron based spectroscopy and low-energy electron microscopy (LEEM) imaging studies of sample surface for ferroelectric domain structure in single crystals and thin films. Preliminary results show LEEM images indicating presence of 180 degree ferroelectric domain structure bellow Curie temperature and temperature dependent surface reconstruction from LEED patterns. Photoemission and x-ray absorption spectroscopy of electronic structure indicate relations between strain and crystallographic structure of epitaxial thin films grown on different substrates. The goal of this study is better understanding the interface effects and spin ordering in multiferroic heterostructures vs single crystals. We acknowledge ARO for support for this work.
4:45 PM - I7.7
Sintered Magnetoelectric Particulate Composties.
Shashank Priya 1 , Vishwas Bedekar 1
1 CEHMS, Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia, United States
Show AbstractIn this presentation, we present our results on sintered ME particulate composites with modified microstructure including random polycrystalline structure, polycrystalline laminates, textured laminates, and core-shell laminates. The results clearly delineate the role of various microstructural variables towards the ME response including grain size, composite geometry, composition of individual phases, and crystal orientation. These studies also illustrate the role of interfacial structure towards elastic coupling and results will be discussed with reference to nanoscale composite architectures. We have been successful in designing composite piezoelectric – magnetostrictive core-shell nanoparticles which can be assembled in various configuration allowing us to study the ME response as a function of composite architecture. A brief description of the analytical model developed to explain and predict the behavior of composites will be provided.
5:00 PM - I7.8
Magnetic Ordering and Exchange Interactions in Multiferroic Bi2FeCrO6 Thin Films.
Riad Nechache 1 , Catalin Harnagea 1 , Mangala P. Singh 2 , Louis-Philippe Carignan 3 , Patrick Fournier 2 , David Menard 3 , Alain Pignolet 1
1 Energie, Materiaux et Telecommunications (EMT), Institut Nationale de la Recherche Scientifique (INRS), Varennes, Quebec, Canada, 2 Département de Physique, Université de Sherbrooke, Sherbrooke, Quebec, Canada, 3 Department of Engineering Physics, Ecole Polytechnique de Montréal, Montréal, Quebec, Canada
Show AbstractComplex oxides exhibit a large range of interesting physical properties; they can be insulating, metallic, semiconductor, supraconductor, ferroelectric, ferri/ferromagnetic as well as they could exhibit phenomena such as supraconductivity, charge ordering (CO), spin-orbit coupling, magnetoresistance and multiferroicity. In the latter case, two or three ferroic properties (i.e. ferroelasticity, ferroelectricity, as well as ferro or –ferri-magnetism) occur simultaneously in the same material. Beside their potential applications, the fundamental physics of multiferroic materials is rich and fascinating. Good magnetic and ferroelectric properties have recently been observed at room temperature in pulsed laser deposition (PLD) grown epitaxial single phase Bi2FeCrO6 (BFCO) thin film, which makes them a promising candidate for building integrated devices. Earlier studies have shown that BFCO exhibits a double perovskite structure with a cationic ordering on the B-site, where the Fe3+ and Cr3+ ions alternate along the crystallographic <111> direction, making up a rock-salt type magnetic cation lattice. BFCO magnetic insulating properties are basically governed by the Goodenough-Kanamori rules, with their ferro-ferrimagnetic coupling arising from a 180° superexchange interaction between Fe3+ and Cr3+ transition metal ions through the oxygen ion of the Fe-O-Cr bond. In order to study the nature of Fe3+-Cr3+ exchange interaction, we grew epitaxial thin films with several thicknesses and on various single crystalline substrates. The variation of the epitaxial strain imposed on the film allows investigating the effect of the structure distortion (i.e. bond distances and angles) on the magnetic interactions between Fe and Cr, as well as on the cationic order. The structural parameters were mainly characterized by X-ray diffraction and reciprocal space mapping. Experimental results about the influence of the epitaxial strain on the films properties and the relationship between them will be presented. A particular attention will be paid on the evolution of the magnetic properties of BFCO thin films with the variation strain states in the film, and the exchange integral J of all films has been estimated from the temperature dependence of the magnetization measurements.
5:15 PM - I7.9
Systematic Engineering of Defects in Controlling Physical Properties of Multiferroic RMnO3 (R=Ho, Er) Epitaxial Thin Films.
Daesu Lee 1 , Heung-Sik Kim 2 , Seung Yup Jang 1 , Gun Woo Joh 3 , Cheol Eui Lee 3 , Jaejun Yu 2 , Tae Won Noh 1
1 , ReCOE & FPRD, Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 2 , CSCMR & FPRD, Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 3 , Spin Dynamics Lab, Department of Physics, Korea University, Seoul Korea (the Republic of)
Show AbstractPhysical properties of multiferroics have been tuned by various control parameters during film deposition. For example, it has been reported that the ferroelectricity in multiferroic thin films can be enhanced using various substrates. Also, using the epitaxial stabilization of thin films, novel multiferroic materials could be synthesized [1, 2]. But, there still exist lots of ways that are applicable to tune the physical properties of multiferroics. We investigated on how to control the multiferroic properties in RMnO3 (R=Ho, Er) via a pulsed laser deposition (PLD) method. As a result, we found a couple of intriguing phenomena that could be systematically controlled by oxygen partial pressure (PO2) during film deposition.Firstly, the magnetic property in ErMnO3 thin films also showed a systematic variation according to PO2 during the deposition. The ErMnO3 thin films deposited at a lower PO2 showed a spin-glass behavior, while the films deposited at a higher PO2 did not [3]. This interesting phenomenon might be induced by defects (especially, oxygen vacancy) in ErMnO3 thin films. Also, more interestingly, the switching behavior of ferroelectric polarization was systematically controlled through a pulsed laser deposition (PLD) of HoMnO3 thin films. As PO2 during the deposition was increased, the switching behavior showed a continuous change from antiferroelectric-like “double” switching to biased “single” switching. This intriguing phenomenon might originate from defect dipoles that consist of Fe impurity and oxygen vacancy in the films. The existence of the defect dipoles was experimentally confirmed by electron paramagnetic resonance spectroscopy. Our experimental observation indicates that the alignment of the defect dipoles in HoMnO3 thin films significantly depends on PO2 during the deposition. This means that the detailed configuration of internal field by defect dipoles can be controlled, which seems promising in application. We also performed first-principles computational calculation in order to explain our observation. Using total energy calculations, we explained the existence of the defect dipoles whose alignment might be changed according to the number of oxygen vacancies. Our study suggests that the multiferroic properties in HoMnO3 and ErMnO3 thin films could be tuned by PO2 during the deposition in a systematic way.[1]J.-H. Lee et al., Advanced Materials 18, 3125 (2006)[2]D. Lee et al., Appl. Phys. Lett. 90, 182504 (2007)[3]S. Y. Jang et al., Appl. Phys. Lett. 93, 162507 (2008)
5:30 PM - I7.10
Raman Scattering Studies of Hydrothermal Derived BiFeO3 Epitaxial Film.
Dibyaranjan Rout 1 , Seung Ho Han 1 , Kyoung-Seok Moon 1 , Suk-Joong Kang 1 , Chase IL Cheon 2 , Ho Gi Kim 1 , Na-Ri Chon 1
1 Materials Science & Engineering, KAIST, Daejeon Korea (the Republic of), 2 Semiconductor and Display Engineering, Hoseo University, Baebang, Asan, Chungnam Korea (the Republic of)
Show AbstractWe report a temperature dependent Raman scattering study of hydrothermal derived multiferroic BiFeO3 (BFO) epitaxial film. Epitaxial film was grown on (100) oriented single crystal SrTiO3 (STO) substrate, polished on one side. Prior to that, a solution was prepared by adding equimolar amounts of Bi(NO3)3●5H2O and Fe(NO3)3●9H2O powders to KOH solution and then stirring vigorously for 30 minutes. The solution was then poured into a 100-ml Teflon-lined stainless autoclave with the fill factor of 40 %. The single-crystal STO substrate was fixed in a Teflon holder with the polished side facing down. The autoclave was placed into a preheated oven at a temperature 200°C for 10 hours. After the synthesis, the films were removed from the holders and cleaned sequentially in acetone, methyl alcohol, and de-ionized water. The film was characterized by x-ray diffraction and Φ-scan experiments to examine the preferred orientation direction, crystal structure and phase purity of the film. The differential scanning calorimetric (DSC) measurement was carried out on the powder specimen prepared by the above described method in the temperature range of room temperature to 550°C to observe the Neel temperature (TN); the antiferromagnetic-paramagnetic phase transition temperature. The Raman spectra were recorded in a wide temperature range from -180°C to 570°C to observe any spectral changes in the vicinity of Neel temperature. The Raman scattering studies revealed significant changes at a cryogenic temperature which tentatively inferred to a further spin reorientation transition exhibited in the BFO film.