Symposium Organizers
Venkatraman Gopalan The Pennsylvania State University
Jon-Paul Maria North Carolina State University
Manfred Fiebig Max-Born-Institut
Ce-Wen Nan Tsinghua University
T1: Multiferroics: Past, Present, and Future Perspectives
Session Chairs
Manfred Fiebig
Venkatraman Gopalan
Monday PM, November 27, 2006
Room 302 (Hynes)
9:30 AM - **T1.1
Historical Milestones on the Route to Maximal Single Phase Multiferroic Complexity.
Hans Schmid 1
1 , University of Geneva, Geneva Switzerland
Show AbstractSome milestones since the nineteen fifties, having lead to the present day level of understanding of complex single phase multiferroics, will be highlighted, partly based on experience gained with the crystal family of boracites M3B7O13X, where M stands for a bivalent 3d-transition metal ion and X for an ion of the halogens F, Cl, Br or I1.Multiferroics have originally been defined as materials with two or more so-called primary ferroic properties - ferro(i)magnetism, ferroelectricity, ferroelasticity - occurring in a single phase1. In recent times ferrotoroidicity, characterized by a spontaneous toroidal moment, was recognized to complete this family of analogues2.The presence of two or more ferroic properties in a single phase is ruled by stringent symmetry and structural requirements. The occurrence of a spontaneous polarization, magnetization and toroidization (toroidal moment)2 in a common phase is restricted to 9 Heesch-Shubnikov point groups, out of a total of 122. Additional ferroelasticity with centro- or noncentrosymmetry of the prototype phase plays a key role for partial or full coupling between named primary ferroic spontaneous quantities and the associated coupled or non-coupled domain switching, respectively3. However, ferroelasticity can sometimes act as a troublemaker.When considering induced toroidal moments, several novel secondary ferroic phenomena can be postulated, such as electrotoroidic, magnetotoroidic, piezotoroidic effects, toroidal optical SHG and toroidal optical rectification2. No experimental evidence for these effects has been reported so far.Measurements of the linear magnetoelectric effect with strong asymmetry of the off-diagonal tensor components have brought evidence in several substances for the presence of a spontaneous or spin-flop-induced toroidal moment4. The recent first monitoring of ferrotoroidic domains5 has brought further, compelling support for this novel type of primary ferroic. Multiferroic complexity increases with the highest allowed number of ferroic domains of an Aizu-species (prototype/ferroic phase point group pair). This number increases with increasing number of types of ferroic order in a single phase and with decreasing symmetry of that phase. Thus a triclinic triple-ferroic-phase perovskite would reach a maximum of 96 domain states in principle. In case of the additional presence of ferrotoroidic domains5,6 that number would be doubled in principle. As a consequence, applications of coupled switching appear feasible only, if Aizu species with a small number of domain states are used. 1. H. Schmid, Ferroelectrics, 162, 317-338(1994); 2. H. Schmid, Ferroelectrics, 252, 41(2001); 3. H. Schmid, Ferroelectrics, 221, 9-17(1999);; 4. Ref. in: H. Schmid in: M. Fiebig et al(eds.), Magnetoelectric Interaction Phenomena in Crystals, 1-34(2004), Kluwer Academic Pub. 5. Bas B. van Aken, M. Fiebig, J.-P. Rivera and H. Schmid, Symposium T; 6. D.G. Sannikov, Ferroelectrics, 291, 157(2003).
10:00 AM - **T1.2
Progress in Thin Film Magnetoelectric Multiferroics.
Nicola Spaldin 1
1 Materials Department, University of California, Santa Barbara, California, United States
Show Abstract10:30 AM - **T1.3
Ferroelectricity from Electron Ordering.
Naoahi Ikeda 1 , Shigeo Mori 2 , Kenji Yoshii 3
1 Physics, Okayama University, Okayama, Okayama pref., Japan, 2 1Department of Physical Science, Osaka Prefecture University, Sakai, Osaka, Japan, 3 Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute , Sayo, Hyogo, Japan
Show Abstract We report a mixed valence oxide RFe2O4 become a ferroelectric originated from the polar electron ordering and free from the ionic displacement. We confirmed Fe3+ and Fe2+ order with a resonant X-ray scattering. The proved ion arrangement possesses an electric polarization. The arrangement of Fe3+ and Fe2+ is explained by the competing interaction between Fe3+ and Fe2+ in triangular lattice. The ferroelectricity arise from the electron distribution shows a direct coupling of degrees of freedom among charge, spin and orbital. RFe2O4 (R=Y or Dy to Lu) is a layered triangular lattice oxide with the spacegroup r-3m(166). The structure is expressed as an alternating stacking of triangular layers composed of rare earth, oxygen and iron ions. The iron triangular plane contains an equal amount of Fe2+ and Fe3+. Comparing to the average valence of Fe2.5+, the Fe2+ and Fe3+ act as an excess half electron (negative charge) and a deficient half electron (positive charge), respectively. Thus the coexistence of Fe2+ and Fe3+ in triangular plane brings a charge frustration on the arrangement for both ions. Taking the competing charge interactions between Fe2+ and Fe3+ into the account the ordering model for Fe2+ and Fe3+ was derived. The model holds an electric polarization since the weight center of Fe2+ and Fe3+ do not coincide. In order to give a proof for the charge ordering we measured the intensity of the superlattice diffraction signal (1/3 1/3 5.5) in the function of X-ray energy near the Fe-K absorption edge. The characteristic enhancements, a maximum at 7.11keV and a minimum at 7.12 keV, show that the difference of the atomic scattering factor for Fe3+ and Fe2+ forms the structure factor of this superlattice. This is the proof for the formation of the superstructure by the ordering from Fe2+ and Fe3+. The index of the super reflection spot indicates that the super cell of Fe2+ and Fe3+ is three times larger than the chemical unit cell within a-b plane. This result gives the same conclusion with the charge ordering model. The presence of the electric polarization by the iron charge ordering gives the consistent explanation for the dielectric response of RFe2O4. For example, LuFe2O4 shows giant dielectric constant up to 5000 with weak temperature dependences below the room temperature. The dielectric relaxation frequency coincides with the iron valence fluctuation frequency, which shows that the polarization switching proceeds with the electron hopping on the iron ions. The electron fluctuation frequency coincides with the characteristic frequency of dielectric response. The electric polarization derived from the pyroelectric current measurement appears below 350K where the charge superstructure develops. This fact indicates that the charge ordering is the order parameter of the electric polarization.reference: N. Ikeda, et al., Nature 436, 1136 (2005).
11:30 AM - **T1.4
Multiferroicity and Colossal Magneto-capacitive Coupling in Transition-metal Compounds.
Joachim Hemberger 1 , Florian Schrettle 1 , Peter Lunkenheimer 1 , Andrei Pimenov 1 , Alexander A. Mukhin 1 2 , Anatoli M. Balbashov 3 , Vladimir Tsurkan 1 4 , Alois Loidl 1
1 Center for Electronic Correlation and Magnetism, University of Augsburg, 86135 Augsburg Germany, 2 , General Physics Institute of the Russian Academy of Sciences, 119991 Moscow Russian Federation, 3 , Moscow Power Engineering Institute, 111250 Moscow Russian Federation, 4 Institute of Applied Physics, Acadeny of Sciences of Moldova, 2028 Chisinau Moldova (the Republic of)
Show AbstractIn recent years multiferroic magnetoelectrics attracted an increasing scientific and technological interest. In this rare class of compounds ferroelectricity (or at least a weak ferroelectric component) and (ferro-)magnetism coexist and both order-parameters are strongly coupled. Prominent examples for such type of materials are the heavy rare earth manganites like TbMnO3, where the partial frustration in the spin-sector leads to spiral magnetic structures inducing finite ferroelectric polarization [1]. The system (Eu:Y)MnO3 [2] offers the possibility to continuously control the orthorhombic distortion of the orbitally ordered perovskite structure and thus to tune the corresponding multiferroic phases without the additional influence of a magnetic rare earth moment. A second example shall be the normal cubic spinels ACr2S4 (A = Cd, Hg, Zn) which in contrast to the manganites do not posses a Jahn-Teller active orbital degree of freedom. CdCr2S4 is a ferromagnetic semiconductor (Tc = 84 K) exhibiting pronounced magneto-resistive and magneto-capacitive effects near the magnetic transition [3]. In this system the dynamics of the dielectric relaxation is strongly influenced by the onset of magnetization.
Besides a detailed characterization of magnetic properties, specific heat, and electric polarization, the discussed materials have been studied using magnetic field dependent broadband dielectric and optical spectroscopy.
[1] T. Kimura et al., Nature 426, 55 (2003)
[2] K. Noda et al., J. Appl. Phys. 99, 08S905 (2006)
[3] J. Hemberger et al., Nature 434, 364 (2005)
This work was partly supported by the Bundesministerium für Bildung und Forschung via grant No. VDI/EKM 13N6917-A and by the Deutsche Forschungsgemeinschaft (SFB 484).
12:00 PM - **T1.5
New Magnetic Twists for Ferroelectricity
Sang-Wook Cheong 1
1 Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey, United States
Show AbstractExtraordinary cross-coupling effects between magnetism and dielectric properties in multiferroics where magnetic and ferroelectric orders coexist have been observed recently. For example, the highly reproducible electric polarization reversal in TbMn2O5 and TbMnO3 and unprecedented large change of dielectric constant in DyMn2O5 and DyMnO3 can be activated by an applied magnetic field (H). Furthermore, acoustic phonons in hexagonal–HoMnO3 can be significantly influenced by H. It turns out that the ferroelectricity in those multiferroics arises from non-colinear magnetic orders with inversion symmetry broken, originating from magnetic frustration. Examples of the non-colinear magnetic orders include spiral magnetic orders.
12:30 PM - **T1.6
Ferroelectricity Induced by Magnetic Order.
Tsuyoshi Kimura 1
1 , Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey, United States
Show AbstractT2: Ferroic Thin Films
Session Chairs
Monday PM, November 27, 2006
Room 302 (Hynes)
2:30 PM - T2.1
Enhanced Dielectric Properties in Ferroelectric Barium Titanate Thin Films.
Jon Ihlefeld 1 3 , Bill Borland 2 , Jon-Paul Maria 1
1 Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 3 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 , Dupont Electronic Technologies, Research Triangle Park, North Carolina, United States
Show Abstract2:45 PM - T2.2
First-Principles Study of Domain Evolution in Ferroelectric Ultrathin Films.
Bo-Kuai Lai 1 , Inna Ponomareva 1 , Ivan Naumov 1 , Igor Kornev 1 , Huaxiang Fu 1 , Laurent Bellaiche 1 , Greg Salamo 1
1 Physics, U of Arkansas, Fayetteville, Arkansas, United States
Show AbstractOver the past decade, ferroelectric thin films have attracted considerable research interest because of their applications in computer memories and radio frequency and microwave devices. With the miniaturization and performance-enhancement trend of the devices, our fundamental understanding on nanoscale ferroelectric thin films is extremely critical to push forward the existing technology and explore new possibilities of ferroelectric applications. The aim of this work is to use first-principles method to reveal and provide unprecedented detailed atomistic features (which are rather challenging to extract from measurements) of the evolution of recently discovered periodic 180o stripe domains in ferroelectric ultrathin films [Phys. Rev. Lett. 89, 067601 (2002)] under external electric fields. Here, we investigate Pb(Zr0.5Ti0.5)O3 (PZT) films that are grown along the [001] direction (which is chosen to be the z-axis) and assumed to be Pb-O-terminated at all surfaces. They are modeled by 40×24×m supercells that are periodic along the x- and y-axes (which are chosen along the [100] and [010] pseudo-cubic directions, respectively), where m is the number of finite (001) B-layers along the non-periodic z-axis. We use the total energy provided by an effective Hamiltonian into Monte-Carlo simulations. Mechanical and electrical boundary conditions are chosen to be close to realistic thin films: the misfit (compressive) strain is –2.65% and the screening corresponds to 81% of the maximum depolarizing field. The external electric field (Ez) is applied along the z-axis. Without the external electric field, the PZT ultrathin films having a thickness of 20 Å form periodic stripe domains with periodicity of 8 unit cells (32 Å). Each period consists of two stripe domains with (mostly) opposite out-of-plane dipoles alternating along the x-axis. As the electric field increases, the domain evolution is rather unusual and involves: (1) the lateral growth of majority dipole domains at the expense of minority domains with the overall stripe periodicity remaining unchanged; (2) the creation of surface-avoiding nanobubbles via the “breaking” of minority stripe domains; and (3) the formation of a single monodomain state. We will also discuss its analogies/differences with (i) ferroelectric thin films made of BaTiO3 and (ii) ferromagnetic thin films under magnetic field. In summary, the domain evolution of epitaxial ferroelectric ultrathin films under an applied electric field and the corresponding atomistic insight have been revealed using first-principles. [Phys. Rev. Lett. 96, 137602 (2006)] We hope that our predictions, and in particular the formation of nanobubbles, will be confirmed soon and will lead to further investigations on the fascinating topic of domain structures in low-dimensional ferroelectrics.
3:00 PM - **T2.3
Phase-field Approach to Predicting Domain Structures in Nanoferroics
Y. Li 1 2 , S. Choudhury 1 , J. Zhang 1 , A. Soukiassian 3 , J. Haeni 1 , A. Vasudevarao 1 , D. Tenne 3 , F. Zavaliche 4 , E. Chu 4 , K. Choi 5 , Q. Jia 2 , C. Eom 5 , R. Ramesh 4 , X. Xi 3 1 , V. Gopalan 1 , D. Schlom 1 , Long-Qing Chen 1
1 Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States, 2 Division of Material Science Technology, Los Alamos National Lab, Los Alamos, New Mexico, United States, 3 Physics, Penn State University, University Park, Pennsylvania, United States, 4 Materials Science and Engineering, UC Berkeley, Berkeley, California, United States, 5 Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractThis talk will briefly review our recent work on theoretical predictions of domain structures and switching in nanoferroics using the phase-field approach. Examples to be discussed include ferroelectric and multiferroic thin films such as BaTiO3, PbTix Ti1-xO3, BiFeO3, SrTiO3, BaTiO3/CoFe2O4 nanocomposites and BaTiO3/SrTiO3 superlattices. In this approach, a nanoscale domain structure is described using a set of spatially inhomogeneous distributions of order parameters such as polarization, magnetization, antiferrodistortion, and strains. Their temporal evolution and relaxation toward are obtained by solving the coupled time-dependent Ginzburg-Landau equations and/or Landau-Lifshitz Gilbert equations as well as the electrostatic, magnetostatic, and mechanical equilibrium equations. For a given set of electrical, magnetic and mechanical boundary conditions, it has the advantage of not only predicting phase transition temperatures but also domain structures without a priori assumptions on the domain states and domain wall orientations. In particular, the roles of strain, film orientation and electrical boundary conditions in the domain structures and domain switching will be discussed. The predicted transition temperatures and domain structures show excellent agreement with available experimental measurements and observations in the same systems.
3:30 PM - T2:ThnFilm
Break
4:30 PM - T2.4
Enhanced Dielectric and Pyroelectric Response from Epitaxial Ferroelectric Films on Anisotropic Substrates.
Gursel Akcay 1 , Ibrahim Misirlioglu 1 , Pamir Alpay 1
1 Materials Science and Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractWe develop a thermodynamic model to determine the polarization, dielectric permittivity, tunability and pyroelectricity of epitaxial ferroelectric films grown on orthorhombic substrates. Orthorhombic substrates induce anisotropic in-plane stresses in the film that can be described using two distinct misfit strains. In particular, we study the film thickness dependence of the dielectric tunability and the pyroresponse in epitaxial Ba0.6Sr0.4TiO3 and BaTiO3 films on NdGaO3 substrates in accordance with the experimentally established epitaxial relation (110)Film//(001)Substrate. The analysis takes into account the thickness dependence of the internal stress state due to the anisotropic relaxation of epitaxial stresses through the formation of misfit dislocations along the two in-plane directions. We predict significant improvement in the pyroelectricity and tunability of both films with increasing film thickness compared to the similar films grown on cubic substrates.
4:45 PM - T2.5
Topotactic Anion Exchange – A New Route to Epitaxial Oxides.
Mark Zurbuchen 1 , Darrell Schlom 2
1 Microelectronics Technology Department , The Aerospace Corporation, El Segundo, California, United States, 2 Department of Materials Science and Engineering, The Pennsylvania State University, Oak Ridge, Tennessee, United States
Show AbstractThe standard approach to depositing epitaxial oxide films is to deliver metal atoms and oxygen simultaneously to a substrate surface. This leads to the problematic constraint that a substrate must be stable under the oxidizing conditions of deposition, making it very difficult to grow epitaxial oxides on certain substrates. Direct growth, however, is not the only option. Topotactic anion exchange offers an alternative route.There exist certain material systems which share a common cation substructure across a wide range of chemistries, which also exhibit wide ranges of solid solubility with one another. But, a crystal of one pure composition, for example a nitride, cannot in principle be transformed to an oxide through a purely diffusive anion exchange reaction, because the large change in lattice parameter from one phase to the other leads to excessive lattice strain, and therefore to mosaic texture and cracking of a film or crystal. However, wide solid solubility between several structurally similar systems enables tuning of the lattice parameter via anion alloying. Thus, one can synthesize a nonoxide material having the same lattice parameter, and having the same cation substructure, as a corresponding oxide material. This enables a topotactic anion exchange – the product crystal inherits its orientation and texture from the precursor crystal – because the change in lattice parameter between precursor and product is zero. No long-range lattice strain develops upon anion exchange.Applications of this new synthesis route are extensive. The approach could enable straightforward growth of epitaxial oxides and epitaxial oxide template layers on oxidation-sensitive substrate materials, such as Si, GaAs, GaN, Cu, Ni, and many others. Oxide template layers grown by this method can also retain strong texture despite misfit between substrate and oxide film. The approach can also lead to increased control of strain in films, by tailoring precursor anion chemistry to control the relative change in lattice parameter between precursor and product. Stronger orientation control than is currently achievable is also possible on some substrates. Synthesis of metastable phases is enabled via the approach. The theory of topotactic anion exchange will be discussed in detail, and results of the growth and characterization of numerous films demonstrating the power of this approach will be presented.
5:00 PM - T2.6
Deposition and Properties of Multiferroic Epitaxial Pb(Fe1/2Nb1/2)O3 Thin films by Pulsed Laser Deposition
Li Yan 1 , Jiefang Li 1 , Dwight Viehland 1
1 Materials Science and Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States
Show AbstractEpitaxial Lead Ion Niobate (Pb(Fe1/2Nb1/2)O3 or PFN) thin films are deposited on (001), (110) and (111) SrTiO3 substrates with SrRuO3 as bottom electrodes. The structural, ferroelectric and ferromagnetic properties will be reported. The resistivity of PFN thin film can reach up to 10^10 Ω cm; the saturated polarization is increased dramatically comparing with bulk PFN single crystal and ceramics; a weak ferromagnetic moment is measured which is dependent on epitaxial stress; the lattice structures of PFN thin films are different in three substrate orientations.
5:15 PM - T2.7
Non-Linear Optical probing of MultiFunctionality and Phase Transition in PbVO3 Thin Films
Amit Kumar 1 , Sava Denev 1 , Lane Martin 2 , Ramamoorthy Ramesh 2 , Venkatraman Gopalan 1
1 Materials Science and Engineering, Pennsylvania, University Park, Pennsylvania, United States, 2 Materials Science and Engineering, University of California , Berkeley, Berkeley, California, United States
Show AbstractLead vanadate (PbVO3) , a relatively new perovskite material, has been predicted to be a multiferroic exhibiting simultaneous ferroelectric and antiferromagnetic ordering. Experimental confirmation of multiferroicity has been difficult with conventional electrical and magnetic measurements. In this work, nonlinear optical techniques have been employed to study the electrical polarization and magnetic ordering in single phase, fully epitaxial thin films of PbVO3 grown using pulsed laser deposition. This growth realizes the first production of PbVO3 outside of high-temperature and high-pressure techniques through growth of epitaxial thin films on LaAlO3 (001), LaAlO3/Si (001), NdGaO3 (110), and SrTiO3 (001) single crystal substrates. Structural analysis of the PbVO3 thin films using transmission electron microscopy, x-ray diffraction, and Rutherford backscattering spectroscopy reveals films that are single phase, highly crystalline, and have a tetragonally distorted perovskite structure with a = 3.79Å and c = 5.02Å (c/a = 1.32). Using optical second harmonic generation (SHG), we have determined a tetragonal point-group symmetry of 4mm for PbVO3 grown on different substrates which confirms the presence of non-centrosymmetry, as imaged via TEM, which in turn gives rise to electrical polarization. As the film growth direction is along the c-axis which is also the direction of the structural distortion and therefore the electrical polarization in these film, SHG measurements were performed in tilted geometry and used to extract effective nonlinear optical coefficients for the film at different temperatures ranging from 4 K to 400 K. We also show a distinct anomaly in the SHG intensity and nonlinear optical coefficients at ~100 K for these films, which suggest a possible magnetic transition near this temperature. The magnetic symmetry has been analyzed on the basis of the symmetry of the SHG response, and determined to be either G-type or a spin glass system. This matches well with the few theoretical treatments done on PbVO3 to this point which note that both C and G-type antiferromagnetic order are the likely ground states at low temperatures. Theoretical modeling of the SHG response is presented that yields quantitative measurements of effective nonlinear optical coefficients as a function of temperature.
5:30 PM - T2.8
Antiferroelectricity in Multiferroic BiCrO3 Epitaxial Films.
Dae Ho Kim 1 , Ho Nyung Lee 1 , Maria Varela 1 , Hans Christen 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show Abstract5:45 PM - T2.9
Effects of Dynamic Strain in Magnetic Films on Piezoelectric Crystals.
Kathrin Dorr 1 , Christian Thiele 1 , Bilani Orkidia 1 , Ludwig Schultz 1
1 , IFW Dresden, Dresden Germany
Show AbstractT3: Poster Session: Multiferroics
Session Chairs
Tuesday AM, November 28, 2006
Exhibition Hall D (Hynes)
9:00 PM - T3.1
Magnetic and Ferroelectric Properties of YMnO3 Epitaxial Thin Films.
Kazuhiro Maeda 1 , Takeshi Yoshimura 1 , Norifumi Fujimura 1
1 , Osaka Prefecture University, Sakai Japan
Show AbstractA material group called multiferroics has attracted considerable attention due to their potential for future computing application. Multiferroics have multiple simultaneous properties such as ferroelectricitiy, ferromagnetism, ferroelasticity and show cross-correlation among the properties. In magnetoferroelectric multiferroics, a magnetic field may control the electric polarization or an electric field may control the magnetization.In this study, we focused on YMnO3, which is a hexagonal RMnO3 compound and has simultaneous antiferromagnetic and ferroelectric properties. Recently, cross-correlation in the magnetic-dielectric properties on hexagonal RMnO3 single crystals including YMnO3 has been reported. In single crystals of YMnO3 and LuMnO3, the dielectric permittivity is largely reduced below the antiferromagnetic Néel point [1]. We examined the relationship between the ferroelectric domain switching and the ordering of magnetic moment using YMnO3 epitaxial films.YMnO3 epitaxial films were deposited by pulsed laser deposition method. To optimize the deposition condition, we analyzed the plasma plume by optical emission spectrometry. It was found that with increasing the laser energy density, the amount of atomic oxygen was increased and the leakage current of the films was decreased. YMnO3 epitaxial films showed distinct ferroelectricity with a spontaneous polarization of 4.2μC/cm2. Moreover the films showed magnetic phase transition near 130K. On the temperature dependence of the maximum dielectric permittivity on the C-V characteristics, which is attributed to the ferroelectric polarization switching, anomaly was observed below the magnetic phase transition near 130K. This result suggests that the ferroelectric polarization switching was suppressed by the ordering of magnetic moment. [1] T. Katsufuji, S. Mori, M. Masaki, Y. Moritomo and H. Takagi: Phys. Rev. B. 64 (2001) 104419.
9:00 PM - T3.10
Photoassisted Polarization Switching in BiFeO3 Thin Films Observed by Terahertz Radiation.
Kouhei Takahashi 1 , Masayoshi Tonouchi 1
1 , Institute of Laser Engineering, Osaka University, Suita, Osaka, Japan
Show AbstractWe have previously reported the first finding of terahertz (THz) radiation from photoconductive switches fabricated on ferroelectric BiFeO3 thin films excited by femtosecond laser pulses [1]. The THz radiation characteristics of BiFeO3 exhibited various intriguing features due to its uniqueness of THz radiation originating from an ultrafast modulation of spontaneous polarization Ps. Here, we have further measured the detailed THz radiation characteristics and observed an interesting phenomenon where carrier excitation triggered by laser illumination seems to greatly enhance the effective electric field applied to the film.Since THz radiation results from the ultrafast modulation of Ps, we can observe THz radiation from BiFeO3 photoconductive switches even under the absence of an external bias electric field Ebias. In other words, the electric field derived from Ps substitutes Ebias, which is essential for THz radiation in the case of nonferroelectric materials. Accordingly, the THz amplitude ETHz measured at zero-bias shows a clear hysteresis similar as the well-known P-E hysteresis curve when we plot ETHz as a function of the initially applied Ebias. Now, although strongly sample dependent, BiFeO3 is known to have a large coercive field compared to the other ferroelectrics [2]. Indeed, the present BiFeO3 thin films grown on (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates did not show a complete saturation of ETHz even when a rather high Ebias of ±200 kV/cm was applied to the film. However, a striking feature was observed when the film was poled under a different circumstance. The two poling treatment we compared here is (a) applying Ebias at dark, which is the usual case, and (b) applying Ebias with light (the light source used here is the second harmonic of a mode-locked Ti:Sapphire laser with a center wavelength of 800 nm, repetition rate of 82 MHz, and pulse width of 100 fs). In the latter case, ETHz showed a complete saturation by applying only Ebias of several 10 kV/cm, which is in contrast to the former case explained above. This implies that carrier excitation by laser illumination enhances the effective electric field applied to the film and promotes the switching of Ps. We also confirmed that an extremely weak laser power of 1 mW is sufficient to trigger such photoassisted polarization switching effect.[1] K. Takahashi et al., Phys. Rev. Lett. 96, 117402 (2006).[2] J. Dho et al., Adv. Mater. 18, 1445 (2006).
9:00 PM - T3.11
Ferroelectric Domain Structure and Switching in Epitaxial BiFeO3 Films with Different Crystallographic Orientations.
M.P. Cruz 1 2 , Y. Chu 1 , F. Zavaliche 1 , P. Yang 1 , G. Pabst 1 , R. Ramamoorthy 1
1 , UC-Berkeley, Berkeley, California, United States, 2 , Centro de Ciencias de la Materia Condensada (CCMC)-UNAM, Ensenada, B.C., Mexico
Show AbstractThe ferroelectric domain structure and polarization switching mechanisms in epitaxial BiFeO3 films grown on (001), (110) and (111) oriented SrTiO3 substrates have been investigated by piezoelectric force microscopy. The ferroelectric polarization vector points toward the SrRuO3 bottom electrode in all films. Four and two polarization variants were observed in films grown on (001) and (110) oriented SrTiO3, respectively. (111) oriented films exhibited only one polarization variant, whose direction is normal to the surface. Polarization switching was investigated by electrically poling the films with a dc bias applied to the conducting scanning probe. The 180° switching mechanism was seen in all three oriented films. 109° switching was observed in the (110) and (001) oriented BiFeO3 films, while the 71° switching was only seen in the (001) oriented films. The large strain in the (001) films associated with ferroelastic switching was reflected in a higher out-of-plane converse piezoelectric response (~60 pm/V) than in the other films. Moreover, since more energy is required to ferroelastically switch the domains, the (001) oriented films showed the largest coercive field as well (~250 kV/cm). The 109°-domain switching in the (110) films was metastable and it relaxed by a further 71° rotation (to complete the 180°-reversal). This relaxation was found to be field and microstructure dependent. This work has been supported in part by ONR, under a MURI program and by LBL-LDRD program.
9:00 PM - T3.12
Domain Structure and Defects in Epitaxial BiFeO3 Films Grown on Vicinal SrTiO3 Substrate.
Qian Zhan 1 , Ying-Hao Chu 1 , Rong Yu 2 , Rasmi R. Das 3 , Dong Min Kim 3 , Chang Beom Eom 3 , Ramamoorthy Ramesh 1
1 , UC Berkeley, Berkeley, California, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 , University of Wisconsin, Madison, Madison, Wisconsin, United States
Show Abstract9:00 PM - T3.13
Preparation of BiFeO3 Thin Films on Membrane Structure.
Seiji Nakashima 1 , Kwi-Young Yun 1 , Yoshitaka Nakamura 1 , Masanori Okuyama 1
1 Graduate school of engineering science, Osaka University, Toyonaka, Osaka, Japan
Show AbstractMultiferroic materials which have feroelectricity, ferromagnetism (antiferromagnetism) and ferroelasticity simultaneously have attracted much attention as material 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 ~ 152μC/cm2) in thin film form1). Such a huge polarization of BFO thin film is strongly affected by the stress from substrate and bottom electrode, but the mechanism has not been clarified completely yet. In this study, we have investigated influence of the stress from substrate and bottom electrode by depositing BFO thin films on membrane structures. Membrane structure which size is 5mm x 8mm was fabricated by etching Si of Pt(200nm)/TiO2(20nm)/SiO2(600nm)/Si(625μm) substrate using 95oC TMAH (Tetramethyleammonium Hydroxide) (25%) for 12 hr. BFO thin films with a thickness of 250nm on the membrane and Pt/TiO2/SiO2/Si substrate were deposited by pulsed laser deposition (PLD) technique using a ArF excimer laser (λ=193nm). Substrate temperature and oxygen pressure were 450oC and 0.03Torr respectively. XRD patterns show that BFO thin films on the membrane and Pt/TiO2/SiO2/Si substrates were polycrystals of only perovskite phase. (There were no diffraction peaks from non perovskite phase such as Bi2O3 or orthorhombic Bi2Fe4O9.) XRD pattern of BFO thin film on the membrane was slightly shifted to lower angle, compared to that on Pt/TiO2/SiO2/Si substrate. It shows that BFO thin film on the membrane has compressive stress from Pt bottom electrode, which is attributed to the difference of thermal expansion between BFO and Pt. Thermal expansion of Pt/TiO2/SiO2/Si substrate depends mainly on that of Si. However, in the case of the membrane, it depends on that of Pt. On the other hand, thermal expansion coefficient of Si is smaller than that of Pt. Therefore, compressive stress of BFO on the membrane is larger than that on Pt/TiO2/SiO2/Si substrate. Reference1)M.Okuyama, K.Y.Yun and D.Ricinschi, Int. Symp. on Integrated Ferroelectrics, 9-564-I, Honolulu, April, 2006
9:00 PM - T3.14
Structural and Electrical Characteristics of La/Mn Modified BiFeO3 Nanoceramics.
Ram Katiyar 1 , Dillip Pradhan 1 , R. Choudhary 1
1 Department of Physics, University of Puerto Rico, San Juan, PO Box-23343, Puerto Rico, United States
Show Abstract9:00 PM - T3.15
Ferroelectric and Magnetic Properties of La-modified BiFeO3 Thin Films Prepared by the Pulsed Laser Deposition Method
Guanjun Zhang 1 , Jinrong Cheng 1 , Rui Chen 1 , Shengwen Yu 1 , Zhongyan Meng 1
1 , Shanghai University, Sahnghai China
Show Abstract9:00 PM - T3.16
Effect of Stain on Texture in Multiferroic BiFeO3 Thin films Using X-ray Microdiffraction.
Chung Wung Bark 1 , Yang Mo Koo 1 , Nobumichi Tamura 2 , Sang Woo Ryu 1 , Hyun Myung Jang 1
1 Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, Kyungsangbuk-Do, Korea (the Republic of), 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show Abstract Recently, multiferroic materials, which two or more of the properties of magnetism and ferroelectricity and ferroelasticity coexist, have taken much attention due to the potential technological applications. There has been recent research interest in a number of prototypical magnetic ferroelectrics including BiMnO3, YMnO3, and etc. However, in any cases of the previously reported compounds, either the P–E or the M–H curve has been reported at the room temperature. Only BiFeO3 has both ferroelectricity and ferromagnetism simultaneously at room temperature. The formation, movement and interaction of domains have a largely effect on behavior of a multiferroic. Therefore, it is crucial that the micromechanics of domains and their effect on internal stresses in multiferroics be understood. The BiFeO3 thin films on SrTiO3 (001) substrates fabricated by PLD (Pulsed Laser Deposition) method. The synchrotron radiation source of beam line 7.3.3.2 at the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, was used for the reflection Laue experiment. The data were analyzed with an indexing software using non-linear least-squares refinement, XMAS (X-ray Microdiffraction Analysis Software). Geometrical calibration parameters were determined by using SrTiO3 crystal beneath thin film. This crystal also used as a reference from strain calculations. The calculated atomic positions which were carried out within a LSDA (Local Spin-Density Approximation) were used. As a result, the crystal orientation and the triaxial deviatoric strain tensor were obtained for every scanned position. In all the scanned grains, the indexation of the Laue patterns show that the grains were confirmed that had a crystal orientation of (001) and others were had the orientation of (101). The local distribution of the deviatoric component the residual strain tensor along the x axis obtained from the two dimensional scan of the top surface was represented. This clearly indicates that the observed residual strain of grains which had a crystal orientation of (001) is quite larger than that of (101). Epitaxial constraint has an effect on crystal structure distortion. Then, the crystal structure is distorted from the rhombohedral along the (001). The integrated average value of residual strain was 6.38 x 10-3 from all of (001) grains and 5.61 x 10-3 from all of (101) grains. (101) texture has the lower strain than (001) texture. The (101) texture is form to provide epitaxial strain relief between substrate and film.
9:00 PM - T3.17
Enhancement of Electrical and Magnetic Properties of Rare Earth doped BiFeO3 Multiferroics
Ratnakar Palai 1 , Suprem Das 1 , P. Dobal 1 , P. Bhattacharya 1 , Ram Katiyar 1 , W. Iwamoto 2 , C. Rettori 2 , P. Pagliuso 2
1 Department of Physics, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Instituto de Fisica, UNICAMP, Campinas, SP, Brazil
Show AbstractThe feasibility of future spintronic devices using multiferroic BiFeO3, a single phase naturally occurring material, is still debated because of its high leakage current, weak ferroelectricity, and lack of understanding of origin of magnetism. However, alternative approaches of increasing polarization and decreasing the leakage current can be possible by cationic doping with other elements. In order to investigate the effect of doping on the ferroelectric and ferromagnetic properties we have synthesized La-doped BiFeO3 (La- on Bi site) and La and Cr- doped BiFeO3 (La- on Bi site and Cr- on Fe site) in both polycrystalline and epitaxial thin films forms using pulsed laser deposition (PLD). The polycrystalline films were grown on Si/SiO2/TiO2/Pt substrates and the epitaxial films were grown on <100> oriented SrTiO3 substrates. The structural and microstructural studies of these films were carried out using X-ray diffraction technique, micro-Raman spectroscopy, and atomic force microscopy (AFM). It is found that La- substitution enhanced the multiferroic properties of BiFeO3 and reduce the leakage current by four to five order of magnitude at a field 50 kV/cm. Further enhancement of properties were observed by doping in both Bi- and Fe-sites with La- and Cr- respectively. The higher values of polarization and magnetization in epitaxial films compared to polycrystalline counterparts were explained on the basis of the structural studies and epitaxial strain between the film and the substrate.
9:00 PM - T3.18
Integration of Ferroelectric BiFeO3 Thin Film on Semiconductor GaN.
Seung-Yeul Yang 1 , W. Tian 2 , Q. Zhan 1 , Y. Chu 1 , M. Cruz 1 3 , K. Lee 1 , D. Schlom 2 , R. Ramesh 1
1 Materials Science and Engineering, U.C. Berkeley, Berkeley, California, United States, 2 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Centro de Ciencias de la Materia Condensada, CCMC-UNAM, Ensenada , B.C., Mexico
Show AbstractIntegration of ferroelectric thin film with semiconductor leads to a wide variety of device applications such as optoelectronic applications and memory storage devices. More recently, the ferroelectric /semiconductor GaN heterostructure system is being investigated due to the high thermal conductivity, breakdown voltage and chemical and mechanical stability. Perovskite BiFeO
3 (BFO) has attracted great attention due to its large ferroelectric polarization and very high order temperatures (ferroelectric Curie temperature T
c = 1030K), which enables BiFeO
3 to be the most prospective candidate as a ferroelectric layer for high temperature device applications.In the present work, we demonstrate the growth of BiFeO
3 thin film using liquid delivery metalorganic chemical vapor deposition (MOCVD) on (0001) GaN/sapphire substrate by epitaxial SrTiO
3 buffer layers with various orientations. These buffer layers allow the epitaxial BiFeO
3 film growth on GaN, whereas polycrystalline BiFeO
3 films were grown on bare GaN surface. The sharp piezoelectric response and square hysteresis loops were obtained with remanent polarization (P
r) of ~80 μC/cm
2 from (111)BiFeO
3 / (111)SrRuO
3 / (111)SrTiO
3 / TiO
2 / (0001)GaN heteroepitaxial structure. Moreover, the microstructure and electrical properties of directly integrated BiFeO
3 on GaN by using ultra thin buffer layers will be discussed.
This work has been supported by the ONR under a MURI program. The authors acknowledge support of the staff and facilities at the National Center for Electron Microscopy, Lawrence Berkeley National Laboratory.
9:00 PM - T3.19
Enhanced Ferroelectric Properties of Epitaxial BiFeO3 Thin Films on Si.
Rasmi Das 1 , Dong-Min Kim 1 , Seung Hyub Baek 1 , Chang-Beom Eom 1 , Venu Vaithyanathan 2 , Darrell Schlom 2 , Yanbin Chen 3 , Xiaoqing Pan 3 , Florin Zavaliche 4 , Seungyeul Yang 4 , R. Ramesh 4
1 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Materials Science and Engineering, The University of Michigan, Ann Arbor, Michigan, United States, 4 Department of Materials Science and Engineering, University of California, Berkeley, California, United States
Show Abstract9:00 PM - T3.2
Capacitance Tunability of Magneto-electric Material:Cr2O3 using Ferromagnetic (La,Sr)MnO3 Electrode.
Takeshi Yokota 1 , Takaaki Kuribayashi 1 , Takeshi Shundo 1 , Yasutoshi Sakakibara 1 , Keita Hattori 1 , Manabu Gomi 1
1 Environmental and Materials Engineering, Nagoya Institute of Technology, Nagoya, Aichi, Japan
Show Abstract9:00 PM - T3.20
Synthesis of Multiferroic BiFeO3 Thin Films by Flux-Mediated Epitaxy (FME)
Sung Hwan Lim 1 , Makoto Murakami 1 , Shigehiro Fujino 1 , Nagarajan Valanoor 2 , Manfred Wuttig 1 , Ichiro Takeuchi 1 , Lourdes Salamanca-Riba 1
1 Materials Science and Engineering, University Of Maryland, College Park, Maryland, United States, 2 School of Materials Science, University of New South Wales, Sydney, New South Wales, Australia
Show Abstract We have fabricated multiferroic BiFeO3 thin films by using the novel flux-mediated epitaxy (FME) technique, in which a film grows from flux on the surface. In this method, vapor from a Bi1.1FeO3, target material diffuses into the flux material and solidifies on a predeposited seed layer of BiFeO3. This procedure can reduce the instability of direct phase transformation from the vapor to the solid. High quality single crystalline BiFeO3 thin films were fabricated on SrRuO3 buffered SrTiO3 (001) substrates. To optimize deposition conditions, the combinatorial deposition technique with temperature and composition gradients on the same sample was used. The oxygen pressure and substrate temperature were varied in the ranges of 0.03 – 3 Torr and 600 – 800 °C, respectively. The structural properties of the films were studied using transmission electron microscopy, x-ray diffraction, atomic force microscopy, and energy dispersive x-ray spectroscopy. By using the FME method, we observed marked improvement in the crystallinity of BiFeO3 films. The peak intensity of BiFeO3 in x-ray diffraction increased more than 20% and the lattice constant was closer to the bulk parameter compared to films grown by the normal pulsed laser deposition technique. The grain size increased approximately from 0.2 to 2 μm. The physical properties of the films are being characterized using piezo force microscopy, and SQUID.This work was supported by NSF MRSEC under account No. DMR-05-20471 and the W. M. Keck Foundation.
9:00 PM - T3.24
Structural and Magnetic Properties of Nanogranular BaTiO3-CoFe2O4 Thin Films Deposited by Laser Ablation on Si/Pt Substrates.
J. Barbosa 1 , Bernardo Almeida 1 , J. Mendes 1 , A. Rolo 1 , J. Araújo 2 , J. Sousa 2
1 Physics, Minho University, Braga Portugal, 2 IFIMUP, Physics, Porto University, Porto Portugal
Show AbstractThe synthesis of materials that exhibit simultaneous ferromagnetic and ferroelectric characteristics has been attracting much scientific and technological interest. In these multiferroic materials, the coupling between the magnetic and electric degrees of freedom, the so-called magnetoelectric effect, may give rise to new physical phenomena and applications.Recently, nanostructured multiferroic composites formed by the combination of a piezoelectric ceramic and a magnetostrictive material, such as in the BaTiO3-CoFe2O4 system, have been deposited in a film-on-substrate geometry. In these systems, the elastic interactions between the phases provides the coupling mechanism inducing a magnetoelectric behavior. As a result, the properties and performance of these nanostructures depend critically on the phase morphology and internal stress distribution, which, in turn, are determined by the elastic phase/phase and phase/substrate interactions.In order to address this problem we have deposited thin film composites of cobalt ferrite (CoFe2O4) dispersed in barium titanate (BaTiO3) matrix, with different cobalt ferrite concentrations (from 20% to 70% CoFe2O4), as well as pure barium titanate and cobalt ferrite thin films (end members). The films were prepared by pulsed laser ablation with a KrF excimer laser (wavelength of 248nm), on platinum covered Si(001) substrates. The oxygen pressure during deposition was in the range 0.4mbar - 2mbar, and the substrate temperature was 600C. The films structure was studied by X-ray diffraction and their surface was examined by scanning electron microscopy (SEM). The magnetic properties were measured in a SQUID magnetometer. The results show that the deposited films are polycrystalline with a slight (111) barium titanate phase orientation and (311) CoFe2O4 phase orientation. The relative intensity of the (111) BaTiO3 increases with increasing CoFe2O4 concentration, while the opposite occurs with the (311) peak relative intensity of the CoFe2O4 phase. The grain sizes measured from the X-ray diffraction peak widths, for both phases, are in the range 40nm to 100nm. However, as the concentration of the cobalt ferrite increases, the grain size of the BaTiO3 phase decreases, from 100nm to 30nm, up to 40% CoFe2O4 concentration beyond which the BaTiO3 grain size has an approximately constant value near 40nm. On the other hand the cobalt ferrite grain size does not show a clear trend with increasing cobalt ferrite concentration, fluctuating in the range 30nm to 40nm. Moreover, the surface of the films shows a smooth and uniform morphology, as observed by SEM, with a small density of droplets.The magnetic measurements show an increase of the magnetic moment from the low concentration region where the magnetic grains are more isolated, towards the bulk value that is attained in the pure CoFe2O4 films. The magnetic behavior of the films is discussed in terms of its correlation with the structural properties of the films.
9:00 PM - T3.25
Structural and Multiferroic Properties of La Modified 0.57BiFeO3-0.43PbTiO3 Crystalline Solutions.
Jianguo Chen 1 , Jinrong Cheng 1 , Dengren Jin 1 , Shengwen Yu 1 , Zhongyan Meng 1
1 , Shanghai University, Sahnghai China
Show Abstract9:00 PM - T3.26
Magnetic and Dielectric Phase Transitions in Multiferroic BiFeO3-ReFeO3-BaTiO3 (Dy, La, Ba) Ceramics.
Jeong Kim 1 , Chae Cheon 2 1 , Nam Kim 2 , Pyong Jang 3
1 Digital Display, Hoseo University, Asan Korea (the Republic of), 2 Materials Sci. & Eng., Hoseo University, Asan Korea (the Republic of), 3 Dept. of Physics, Chongju University, ChongJu Korea (the Republic of)
Show AbstractThe materials exhibiting multiple ferroic properties, such as ferroelectricity, ferroelasticity, and ferromagnetism (or antiferromagnetism) in one phase have been named as the multiferroics. Recently the ferroelectromagnetic materials have became widely known due to their potential applications in the memory devices, sensors, and spintronics. The perovskite type materials provide the vast spectrum of electrical properties covering (anti-) ferroelectric, (anti-)ferromagnetic, metallic, semiconductor, and insulator. Hence the combination of these perovskite members could open various routes for achieving the multiferroic properties in one phase material. Residual magnetic moments at 20 Oe and 8 kOe have been measured using vibrating sample magnetometer (VSM) with increasing temperature up to 600oC. The dielectric constant εr and the loss tangent have been measured using impedance analyzer (10kHz~1MHz) in the temperature range of RT~550oC. Neutron diffraction data were collected using HRPD diffractometer at HANARO in Korea Atomic Energy Research Institute. The neutrons from the HANARO reactor were monochromatized by a vertically focusing composite Ge-monochromator to a wavelength of 1.8348Å. The crystal structure was analyzed by the rietveld profile refinement method using a version 3.2 of the program Fullprof. Dielectric and magnetic properties of the xBiFeO3-yReFeO3-zBaTiO3 (Re=La, Dy, Ba) solid solution ceramics at high temperature range of RT~600oC have been characterized. For more understandings of the multiferroic property, the relation between the crystal structure transition, magnetic transition, dielectric transition with increasing temperature have been analyzed. Residual magnetization Mr under the low and high applied magnetic fields (H = 20Oe, 8KOe) and the dielectric properties, εr and tand, with varying measuring frequency and temperature have been characterized using the vibrating sample magnetometer and LCR meter respectively. The neutron diffraction data has been collected at the temperature range of RT ~ 800oC. The low Re content samples (y = 0, 0.025) show one magnetic transition at temperature range of 410~430oC while the high DF concentration samples (y = 0.05) show an additional transition at 250~290oC. The magnetic transition at 410~430oC corresponds to the crystal structural transition to the tetragonal P4mm from the rhombohedral R-3c, at which the BiFeO3 and the DyFeO3 samples lose their antiferromagnetic ordering. The multiferroic properties will be discussed in relation with the phase transitions of magnetic, dielectric, and crystal structures.
9:00 PM - T3.27
Processing and Characterization of LSMO-Based Multiferroic Composite Ceramics.
Andrei Kholkin 1 , G. Song 1 3 , J. Amaral 2 , V. Amaral 2 , Z. Fu 1 , J. Araujo 4 , J. Sousa 4
1 Dept. of Ceramics/CICECO, University of Aveiro, Aveiro Portugal, 3 School of Material Science and Engng., Sothwest University of Science and Technology, Mianyang China, 2 Dept. of Physics/CICECO, University of Aveiro, Aveiro Portugal, 4 Dept. of Physics/CPF, University of Porto, Porto Portugal
Show Abstract9:00 PM - T3.28
Magnetoelectric Properties of Multiferroic Composites with Pseudo 1-3 Type Structure.
Zhan Shi 1 , Ce-Wen Nan 1 , Jie Zhang 1 , Jing Ma 1 , Jing-Feng Li 1
1 Material Science and Engineering, Tsinghua University, Beijing China
Show AbstractA pseudo 1-3 type multiferroic composite consisting of Pb(Zr,Ti)O3 (PZT) rod array (with base) and Terfenol-D/Epoxy matrix was prepared by the dice-and-fill technique. Simple series and parallel mixture rules well described the measured dielectric and piezoelectric constants. Large magnetoelectric coefficients were observed in the pseudo 1-3 type composite, e.g., over 300 mV/cm.Oe below 40 kHz and over 4500 mV/ cm.Oe at resonant frequency. The ME response strongly depends on the magnetostrictive behavior of the matrix and the volume fraction of PZT rods, which gives us two convenient way to modify their magnetoelectric response. For this pseudo 1-3 type multiferroic composite, the remarkable magnetoelectric response and well-developed fabrication technique are advantageous for their practical applications in piezoelectric-magnetoelectric multifunctional devices and large bandwidth magnetic sensors.
9:00 PM - T3.29
Multiferroic Pb(Zr0.53Ti0.47)O3/NiFe2O4 Sol-gel Thin Films.
Shenqiang Ren 1 , Manfred Wuttig 1
1 Dept. of Materials and Science Engineering, University of maryland, college park, College park, Maryland, United States
Show AbstractPhase-separated multiferroic Pb(Zr0.53Ti0.47)O3/NiFe2O4 thin films on (111)Pt/Ti/SiO2/Si substrates were synthesized by a sol-gel spin-coating technique, as evidenced by x-ray diffraction. The use of sol-gel processing ensured good chemical homogeneity and a relatively low crystallization temperature. The dependence of annealing conditions and microstructure evolution of thin films were examined by Environmental scanning electron microscopy, transmission electron microscopy and atomic force microscopy. Obvious multiferroic behavior has been observed in phase-separated and highly resistive Pb(Zr0.53Ti0.47)O3/NiFe2O4 thin films. These show the coexistence of ferroelectricity and magnetism, possess an anomaly of the dielectric constant in the vicinity of the ferromagnetic Curie temperature, and exhibit magnetoelectric coupling at room temperature.
9:00 PM - T3.3
AFM-Based Simultaneous Measurement of Ferroelectric and Ferromagnetic Domains in Multiferroics.
Brian Piccione 1 , John Blendell 1 , R. Garcia 1 , R. Ramesh 2
1 Materials Science and Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Materials Science and Engineering, University of California, Berkeley, California, United States
Show AbstractA BiFeO3-CoFe2O4 sample grown on SrRu03 by pulsed laser deposition was examined using combined MFM and PFM (both lateral and vertical) to determine the effect of crystallographic arrangement on local strain coupling. Simultaneous measurement of local magnetostrictive and piezoelectric response in a multiferroic composite is expected to yield information on the effect of texture on the coupling mechanics of these new materials. The results of the combined measurements will be correlated to predicted results based on FEA, with the goal of aiding design in applications such as nonvolatile multiferroic memory and novel magnetoelectic sensors.
9:00 PM - T3.30
Magnetoelectric Effects In Multiferroic Compounds And Composites.
Junming Liu 1
1 Department of Physics, Nanjing University, Nanjing 210093 China
Show AbstractMagnetoelectric coupling as well established in multiferroic perovskite oxide compounds and piezoelectric-magnetostrictive composites has been receiving attentions due to its unique application potentials in sensing and actuation technologies. In addition, the rich physics underlying the coupling represents one of the hot topics in the community of condensed matters and materials sciences. We report our recent researches on the magnetoelectric coupling effects in multiferroic perovskite oxides and piezoelectric-magnetostrictive composites. First, the phase transitions associated with ferroelectric and magnetic orderings and magnetoelectric coupling in Pb(Fe1/2Nb1/2)O3 (PFN) single crystals were investigated, demonstrating the coupling-induced weak ferromagnetic transitions in PFN at low temperature. Subsequently, we revealed the enhanced ferroelectricity and spin glass behavior of BiFeO3 (BFO) thin films and nanowires. In particular, we observed interesting application potentials of BFO nanowires as photo-catalysts. Furthermore, we developed a series of piezoelectric-magnetostrictive composite structures in both bulk ceramic and thin film forms. The magnetoelectric effects and inverse magnetoelectric effects as observed in these structures are high enough for practical applications in ultra-weak magnetic field sensing at room temperature. The measured data and associated interpretations will be presented in details in this report.
9:00 PM - T3.31
Giant Magnetoelectric Effect in Novel Metglas/PVDF Laminates with Small DC bias
Junyi Zhai 1 , Shuxiang Dong 1 , Jiefang Li 1 , Dwight Viehland 1
1 MSE, Virginia Tech, Blacksburg, Virginia, United States
Show AbstractThe application of magnetoelectric (ME) sensors and devices is mainly restricted by a large DC magnetic bias (400 Oe – 4000 Oe). Here we report thin (< 100 µm) and flexible ME laminates: high-µ Metglas/high-g31 PVDF composites, and their extraordinary ME performances as (i) the required DC magnetic bias is extreme low: ~8 Oe; (ii) giant ME voltage coefficients of 7.2 V/cm-Oe at low-frequency and 310 V/cm Oe at resonance; (iii) high DC magnetic field sensitivity of 8 nT; and (iv) high AC magnetic field sensitivity of < 7 pT at resonance frequency (47.9 kHz).
9:00 PM - T3.32
Polarization Response to Magnetic Field in Model Multiferroics: A Monte Carlo Simulation.
Qichang Li 1 , Junming Liu 1
1 Department of Physics, Nanjing University, Nanjing 210093 China
Show AbstractMultiferroic materials, which possess two or more order parameters such as polarization, magnetization or strain, have been attracting revived interest due to the gigantic magnetoelectric (ME) effect observed in systems such as TbMn2O5 and CoCrO3 etc. In those materials, a startling change or even reversal of electric polarization induced by magnetic field was found. In this work, we report a Monte Carlo simulation on the magnetically driven ferroelectric polarization of a model multiferroic system in which ferroelectric (FE) order and antiferromagnetic (AFM) order coexist. The Hamiltonian of this model system includes the contributions from the ferroelectric subsystem, the AFM Ising subsystem and an intrinsic coupling between the two subsystems. The magnetic and ferroelectric parameters used in the simulation are chosen so that the Curie point for ferroelectric order TC is smaller than the Něel point TN. We investigated the evolution of electric polarization P in responding to magnetic field H below TC. A magnetic field dependence of electric polarization is obtained, similar to experimental results reported earlier. Since only u2 is included in the coupling term, the flips of the nearest-neighboring Ising spins driven by H just influence the amplitude of the electric polarization. On the other hand, the direction of ui in our model is restricted in one axis, which explains why P does not reverse with H in our model. To simulate the reversal of the polarization driven by H, new mechanism of ME coupling should be considered.
9:00 PM - T3.33
Theory of Spin-charge-orbital State in the Frustrated System RFe2O4.
Sumio Ishihara 1 , Makoto Naka 1 , Aya Nagano 1
1 Physics Department, Tohoku University, Sendai Japan
Show Abstract9:00 PM - T3.34
Nanoscale domain control in multiferroic BiFeO3 thin films
Ying-Hao Chu 1 , Qian Zhan 1 , Lane Martin 1 , Maria Cruz 1 , Pei-Ling Yang 1 , Gary Pabst 1 , Florin Zavaliche 1 , Seung-Yeul Yang 1 , Jing-Xian Zhang 2 , Long-Qing Chen 2 , Darrell Schlom 2 , Ramamoorthy Ramesh 1
1 Department of Physics & Department of Materials Science and Engineering, UC Berkeley, Berkeley, California, United States, 2 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractWe demonstrate an approach to create a 1-dimensional periodic structure of ferroelectric domains in epitaxial BiFeO3 films. By careful control of the growth mechanism for the BiFeO3 and the SrRuO3 bottom electrode, its in-plane lattice parameters have been confined by the underlying DyScO3 (110)O single-crystal substrate enabling the formation of an expitaxial film of (110)O SrRuO3 with a single structural domain. This has been used to provide an anisotropic strain to exclude two of the possible ferroelectric polarization variants and induce a 1-D periodic ferroelectric domain structure in the BiFeO3 films.
9:00 PM - T3.4
Doping Effect on the Charge Ordering in LuFe2O4.
Shigeo Mori 1 , Yoji Matsuo 1 , Y. Horibe 1 , K. Yoshii 2 , N. Ikeda 3
1 Department of Physics, Osaka Prefecture university, Osaka Japan, 2 , JAERI, Hyugo Japan, 3 Deparment of Physics, Okayama University, Okayama Japan
Show Abstract9:00 PM - T3.5
Ferroelectric and Magnetic Characterization of Ferroic Pb(Fe0.5Nb0.5)O3 Ceramics.
Oscar Raymond 1 , Reynaldo Font 2 , Jorge Portelles 2 , Gopalan Srinivasan 3 , Jesús Siqueiros 1
1 Propiedades Opticas, Centro de Ciencias de la Materia Condensada, UNAM, Ensenada, Baja California, Mexico, 2 Física Aplicada, Universidad de la Habana, La Habana, Ciudad de la Habana, Cuba, 3 Physics Department, Oakland University, Rochester, Michigan, United States
Show Abstract9:00 PM - T3.6
Magnetic and Dielectric Properties of Multiferroic TbMnO3 Nanoparticles.
S. Kharrazi 1 , S. Gosavi 1 , S. Kulkarni 1 , Darshan Kundaliya 2 , S. Ogale 2 , T. Venkatesan 2 , S. Park 3 , S. Cheong 3 , J. Urban 4
1 DST Unit on Nanoscience, Department of Physics, University of Pune, Pune India, 2 CSR, Department of Physics, University of Maryland, , College park, Maryland, United States, 3 Department of Physics, Rutgers University, Piscataway, New Jersey, United States, 4 Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft , D-14195 Berlin (Dahlem) Germany
Show Abstract9:00 PM - T3.7
Multiferroic Behavior in Barium Hexaferrite Probed with Optical Second Harmonic Generation
Eftihia Vlahos 1 , Sava Denev 1 , Venkatraman Gopalan 1 , Tsuyoshi Kimura 2
1 Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States, 2 Bell Laboratory, Lucent Technologies, Berkeley Heights, New Jersey, United States
Show AbstractHexaferrite Ba0.5Sr1.5Zn2Fe12O22 is a very promising material, which exhibits significant magneto (ME) effect, that is, the generation of electric polarization (magnetization) by the application of magnetic (electric) field. It was recently reported that the ferroelectric polarization direction in this material can be rotated by an externally applied magnetic field. Using second harmonic generation (SHG), the magnetic point group symmetries and phase transitions under magnetic fields are determined. Theoretical modeling of the SHG behavior is carried out yielding quantitative information about its nonlinear optical coefficients and its changes with temperature and magnetic fields. SHG allows a clean separation of the magnetic and ferroelectric contributions to the multiferroic system.
9:00 PM - T3.8
Improvement of the Crystallinity of BiFeO3 Thin Films Prepared by MOCVD.
Yuzo Tasaki 1 , Toshiaki Kanoko 2 , Shuji Yoshizawa 2
1 , Toshima MFG Co.,Ltd., Higashimatsuyama, Saitama, Japan, 2 , Meisei Univ., Hino, Tokyo, Japan
Show Abstract9:00 PM - T3.9
Synthesis, Structure and Magnetism of BiFeO3 thin films on (LaAlO3)0.3(Sr2AlTaO6)0.7 (100) Substrates.
Dhanvir Rana 1 , K. Takahasni 1 , K. Mavani 1 , I. Kawayama 1 , H. Murakami 1 , M. Tonouchi 1
1 Institute of Laser Engineering, Osaka University, Osaka, Osaka-fu, Japan
Show AbstractA recent upsurge in research on room temperature multiferroic (antiferromagnetic and ferroelectric) BiFeO3 has been motivated by the observation of enhanced ferroelectricity and ferromagnetism in epitaxial thin films [1]. Some of these properties being reported to be thickness dependent remains an issue of contention and deserve further extensive investigations [2]. Furthermore, most of reported studies on BiFeO3 have been performed on the thin films deposited on SrTiO3 substrates. Recently, pure and Mn-doped BiFeO3 thin films were deposited on ((LaAlO3)0.3(Sr2AlTaO6)0.7 (100) [LSAT] single crystal substrates [3]. This offers a further prospect to investigate the multiferroic properties of BiFeO3 thin films in varying epitaxial strain states induced by LSAT substrate. In the present work, we have synthesized BiFeO3 thin films of varying thickness, ranging from 40 nm – 500 nm, on LSAT (100) single crystal substrates, using pulsed laser deposition of a Bismuth-rich, Bi1.1FeO3, multiphase target. We, for the first time, have observed a thin film thickness dependent structural transition from a monoclinically distorted tetragonal phase at a thickness of 110 nm to a rhombohedral phase at a thickness of 80 nm. It is further shown that the in the mixed structural phase region of 80 nm – 110 nm thickness, the phase fraction of rhombohedral structure can be enhanced significantly by increasing the post-deposition O2 annealing pressure from 0.5 kOe to 40 kOe. The room temperature magnetic properties of these films were found to be dependent on thickness – the magnetization increases from 0.04 µB/f.u. for 200nm thin film to 0.14 µB/f.u. for 70nm thin film. In addition for 110 nm thin films, the spontaneous magnetization of the film annealed in ~0.5 kPa O2 pressure (having tetragonal structure) is lesser than that of the film annealed in ~40 kPa O2 pressure (having mixed phase of tetragonal and rhombohedral structures), thus, suggesting that the magnetic properties BiFeO3 films are also dependent on the structure.References - [1]. Wang et al., Science 299, 1719 (2003). [2]. Eerenstein et al., Science 307, 1203a (2005); Wang et al., Science 307, 1203b (2005).[3]. K. Takahashi and M. Tonouchi, Jpn. J. Appl. Phys. (in Press, 2006); K. Takahashi, N. Kida and M. Tonouchi, Phys. Rev. Lett. 96, 117402 (2006).
Symposium Organizers
Venkatraman Gopalan The Pennsylvania State University
Jon-Paul Maria North Carolina State University
Manfred Fiebig Max-Born-Institut
Ce-Wen Nan Tsinghua University
T4/W4: Joint Session: Capacitors
Session Chairs
Tuesday AM, November 28, 2006
Room 302 (Hynes)
9:30 AM - **T4.1/W4.1
An Engineering Perspective: Toward Temperature Insensitive Electric-Field Tunable Material and Devices.
Steven Tidrow 1 , Frank Crowne 1 , Arthur Tauber 1 , Daniel Potrepka 1 , Steven Weiss 1 , Bernie Rod 1
1 Sensors & Electron Devices Directorate, U.S. Army Research Laboratory, Adelphi, Maryland, United States
Show AbstractRecently there has been much interest in electric-field tunable dielectric materials, many from the perovskite family, for use in phase shifters for microwave electronic scanning antenna arrays and for frequency agile components like electric-field tunable filters. Materials that are highly electric-field tunable are typically high dielectric constant materials, ferroelectric or anti-ferroelectric, that are, at least in bulk form, quite temperature sensitive and can be quite lossy with respect to microwave radiation. To reduce temperature sensitivity and microwave losses, these materials are often used in the paraelectric regime, in bulk form, or used as thin films. For operation in the paraelectric regime, atomic substitutions are made in the perovskite structure to drive the Curie temperature to well below the minimum device operating temperature, moreover, additions are often made to improve the material figure of merit through reduction of losses. In both cases, such substitutions and additions lead to materials with significantly reduced tunability, for a given electric-field strength, that may result in poorer device performance especially at higher operating temperatures even though the material may have a higher figure of merit. Thin films, which at present appear to be the preferred configuration for fabrication of devices, are typically nearly temperature insensitive with significantly reduced values of both dielectric constant and tunability. While the reduced dielectric constant is useful from a device perspective, the reduced tunability results in reduction of electrode spacing, higher electric-field strengths (even though lower driving voltages may be used) and ultimately reduced power handling capability. We at the Army Research Laboratory, Sensors and Electron Devices Directorate, have been using a different approach to overcoming the various issues associated with electric-field tunable material and devices. From a material engineering perspective, we have fabricated highly electric-field tunable materials that possess lower dielectric constants, reasonable losses and properties that are nearly temperature insensitive over a large temperature range, -50 to 125 °C. Further, from a device engineering perspective, for enabling a low cost electronic scanning antenna technology, we have been developing a variable true time delay device structure and architecture that may provide significant advantages over a phase shifter technology. In this presentation, we will review, from an engineering perspective, material and device trade-offs, discuss these new highly electric-field tunable nearly temperature insensitive materials as well as compare phase shifter and variable true time delay architectures for achieving an affordable electronic scanning antenna technology.
T5: Bismuth Ferrite and Derivatives
Session Chairs
Tuesday PM, November 28, 2006
Room 309 (Hynes)
9:30 AM - T5.1
Planar Electrode Piezoresponse Force Microscopy to Study Ferroelectric Switching in BiFeO3.
Padraic Shafer 1 , Florin Zavaliche 1 2 , Ying-Hao Chu 1 2 , R. Ramesh 1 2
1 Materials Science & Engineering, University of California, Berkeley, California, United States, 2 Physics, University of California, Berkeley, California, United States
Show AbstractThe coupling of ferroelectric and magnetic order parameters in multiferroic systems is an important phenomenon with exciting technological implications for integrating magnetic devices into microelectronic circuits. Various forms of scanning probe microscopy (SPM) have been used to observe and even manipulate the nanoscale domains that are typically found in magnetoelectric thin films, but existing methods are limited in their ability to characterize the dynamic processes that occur during domain orientation switching. To remedy this limitation, we have developed the technique of planar electrode piezoresponse force microscopy (PE-PFM). Our method relies upon epitaxial, conductive electrodes embedded into the plane of a ferroelectric thin film in order to decouple the electrical stimulus from the SPM cantilever-tip assembly that measures the piezoresponse. SrRuO3 electrodes were defined by photolithography to examine BiFeO3 films, both of which were prepared by pulsed laser deposition on SrTiO3, DyScO3, or GdScO3 single-crystal substrates at temperatures between 600-750 °C. The epitaxial nature of the system permits the domain structure of BiFeO3 to be tailored by the strain, anisotropy, and crystalline orientation of the substrate. Decoupling the stimulus from the SPM tip allows electric fields to be applied within the scanning plane so that time-resolved images can be captured as domain wall motion evolves within that plane. By applying dc electric field pulses (0.01-1000 ms; 25-600 kV/cm) to a BiFeO3 film through embedded SrRuO3 electrodes, we were able to observe switched ferroelectric domains nucleate on one electrode and subsequently grow toward the other electrode. Because PE-PFM does not require a conductive coating that enlarges the SPM tip, our technique offers PFM images with higher spatial resolution than the traditional biased-tip approach. Additionally, the planar electrode setup permits magnetoelectric characterization to be performed as a function of time and electric field strength by magnetic force microscopy, Kerr microscopy, or photoemission electron microscopy using linear or circular dichroism. BiFeO3 is already well known to be multiferroic, having previously been established as a G-type antiferromagnet, with Fe magnetic moments coupled ferromagnetically within pseudocubic (111) planes and antiferromagnetically between planes, where [111]C is the ferroelectric polarization direction. We observed domain switching in BiFeO3 grown on DyScO3(110)O to be predominantly ferroelastic, thus opening the possibility of electrically controlling the orientation of antiferromagnetic ordering in BiFeO3. This effect could be used to switch the magnetic polarization of a ferromagnet that is exchange-biased to BiFeO3. The electrode layout of the PE-PFM setup provides a versatile framework for non-destructive, high-resolution (spatial and temporal) characterization and control of magnetoelectric structures.
9:45 AM - T5.2
Computer Simulation of Ferroelectric Domain Morphologies of Epitaxial BiFeO3 Thin Films.
Jingxian Zhang 1 , Samart Choudhury 1 , Yulan Li 1 3 , Ying-Hao Chu 2 , Florin Zavaliche 2 , Quanxi Jia 3 , Darrell Schlom 1 , Ramamoorthy Ramesh 2 , Long-Qing Chen 1
1 Department of Materials Science and Engineering, Pennsylvania State University, State College, Pennsylvania, United States, 3 MST-STC, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Department of Materials Science and Engineering and Department of Physics , University of California, Berkeley, California, United States
Show AbstractT4/W4: Joint Session: Capacitors
Session Chairs
Tuesday PM, November 28, 2006
Room 302 (Hynes)
10:00 AM - **T4.2/W4.2
Integrated BST Tunable Dielectrics for Frequency Agile GHz Applications.
Paul Clem 1 , Jennifer Sigman 1 , Patrick Finnegan 1 , Chris Nordquist 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractFor development of compact RF electronics with frequency agile properties, materials integration of low loss tunable dielectrics with high conductivity metals is necessary. Methods for integration of tunable dielectric [(Ba,Sr)TiO3, BST] thin films on substrates including silicon, alumina, silicates, and metal foils will be presented. Reducing atmosphere approaches to enable BST integration on base metal foils and electrodes will be discussed, including the interplay between metal reduction and oxide defect chemistry. In thin film form, epitaxial and columnar-grained BST films have been observed to display significantly higher permittivities and tunabilities than otherwise identically-processed randomly oriented, polycrystalline films. This effect will be discussed in relation to the grain size, grain morphology, and domain orientation of the BST films, as determined by microscopy, x-ray diffraction and Raman spectroscopy. Phase shift and Q results for interdigitated capacitors of these films in the 1-10 GHz range will be reported, along with approaches to more temperature-stable tunable capacitor properties. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy''s National Nuclear Security Administration under contract DE-AC04-94AL85000.
T5: Bismuth Ferrite and Derivatives
Session Chairs
Tuesday PM, November 28, 2006
Room 309 (Hynes)
10:00 AM - **T5.3
Multifunctional Oxide Heterostructures.
Ramesh Ramamoorthy 1
1 Depts. of Materials Science and Engineering and Physics, University of California - Berkeley, Berkeley, California, United States
Show AbstractComplex perovskite oxides exhibit a rich spectrum of functional responses, including magnetism, ferroelectricity, highly correlated electron behavior, superconductivity, etc. The basic materials physics of such materials provide the ideal playground for interdisciplinary scientific exploration. Over the past decade we have been exploring the science of such materials (for example, colossal magnetoresistance, ferroelectricity, etc) in thin film form by creating epitaxial heterostructures and nanostructures. Among the large number of materials systems, there exists a small set of materials which exhibit multiple order parameters; these are known as multiferroics. Using our work in the field of ferroelectric and ferromagnetic oxides as the background, we are now exploring such materials, as epitaxial thin films as well as nanostructures. Specifically, we are studying the role of thin film growth, heteroepitaxy and processing on the basic properties as well as magnitude of the coupling between the order parameters. A very exciting new development has been the discovery of the formation of spontaneously assembled nanostructures consisting of a ferromagnetic phase embedded in a ferroelectric matrix that exhibit very strong coupling between the two order parameters. This involves 3-dimensional heteroepitaxy between the substrate, the matrix perovskite phase and spinel phase that is embedded as single crystalline pillars in this matrix. In this talk I will describe to you some aspects of such materials as well as the scientific and technological excitement in this field.
T4/W4: Joint Session: Capacitors
Session Chairs
Tuesday PM, November 28, 2006
Room 302 (Hynes)
10:30 AM - T4.3/W4.3
Fabrication of Frequency Agile Microwave Circuits Using (Ba,Sr)TiO3 Thin Film Capacitors
Jennifer Sigman 1 , Paul Clem 1 , Chris Nordquist 1 , Patrick Finnegan 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractNew materials and new integration schemes are vital to the continued development and improvment cellular, satellite and radar communication systems. We report on our efforts to integrate tunable dielectric (Ba,Sr)TiO3 (BST) thin films into frequency agile microwave circuits. We focus on depositing BST on alumina and through-wafer via hole substrates. Using through-wafer via holes increases the variety of devices that can be realized, but adds complexity for materials integration because the via material is a copper-tungsten alloy. By controlling the processing parameters, namely temperature and oxygen partial pressure, we have successfully deposited quality BST on alumina and through wafer via hole substrates by chemical solution deposition without secondary phases. Initial phase shifter devices have also been successfully fabricated and tested. Both the film properties and device properties are discussed.
T5: Bismuth Ferrite and Derivatives
Session Chairs
Tuesday PM, November 28, 2006
Room 309 (Hynes)
10:30 AM - T5.4
Effects of BiFeO3 Deposition on SrTiO3 Substrates.
Mary Ellen Zvanut 1 , Brian Lassiter 1 , Gregg Janowski 2 , Leonard Brillson 3
1 Department of Physics, University of Alabama at Birmingham, Birmingham, Alabama, United States, 2 Department of Materials and Mechanical Enineering, University of Alabama at Birmingham, Birmingham, Alabama, United States, 3 Center for Materials Research, Ohio State University, Columbus, Ohio, United States
Show AbstractT4/W4: Joint Session: Capacitors
Session Chairs
Tuesday PM, November 28, 2006
Room 302 (Hynes)
T5: Bismuth Ferrite and Derivatives
Session Chairs
Tuesday PM, November 28, 2006
Room 309 (Hynes)
10:45 AM - T5.5
Size Effects in Multiferroic BiFeO3 Thin Films.
Ying-Hao Chu 1 , Tong Zhao 1 , Qian Zhan 1 , Florin Zavaliche 1 , Maria Cruz 1 , Pei-Ling Yang 1 , Lane Martin 1 , Kilho Lee 1 , Seung-Yeul Yang 1 , Wei Tian 2 , Darrell Schlom 2 , Ramamoorthy Ramesh 1
1 Department of Physics & Department of Materials Science and Engineering, UC Berkeley, Berkeley, California, United States, 2 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractT4/W4: Joint Session: Capacitors
Session Chairs
Tuesday PM, November 28, 2006
Room 302 (Hynes)
11:15 AM - **T4.4/W4.4
BST Technology for RF/Microwave Applications.
Robert York 1
1 , University of California - Santa Barbara, Santa Barbara, California, United States
Show AbstractSince the 1990s there has been significant progess in developing high-k, polar and non-polar materials such as (Ba,Sr)TiO3 (BST) and Bi1.5Zn1.0Nb1.5O7 (BZN). BST thin-films have been realized with properties that are especially attractive for high-frequency applications, including: High dielectric constant (200-300): useful for small-area bypass or AC decoupling capacitors Field-dependent permittivity: as much as 3:1 variation in permittivity or capacitance as a function of applied voltage, useful for tunable RF circuits such as phase-shifters, filters, and (VCOs).“Fast” polarization response: allows for rapid tuningGood breakdown fields: typically >1MV/cm, allowing for large bipolar voltage swings and hence good power handling.Reasonable Loss Tangents: typical loss tangents of tan δ < 0.02 up to 10GHz and higher.Combined with a simple manufacturing process and high-quality insulating substrates, BST-based voltage-variable capacitors (varactors) can provide a compelling alternative to semiconductor-based varactors for highly-integrated RF/Microwave circuits. Several companies now provide products for RF applications based on thin-film BST. This talk will review progress in this area, potential applications and RF insertion points in wireless communications, examples of commercial products, and remaining challenges.
T5: Bismuth Ferrite and Derivatives
Session Chairs
Tuesday PM, November 28, 2006
Room 309 (Hynes)
11:30 AM - T5.6
Exchange Bias and Spin Valves Using BiFeO3 Thin Films.
Shigehiro Fujino 1 , Makoto Murakami 1 , Jaeson Hattrick-Simpers 1 , S. Lim 1 , J. Higgins 2 , Lourdes Salamanca-Riba 1 , S. Lofland 3 , Munfred Wuttig 1 , Ichiro Takeuchi 1 2
1 Materials science and engineering, University of Maryland, College Park, Maryland, United States, 2 Center for Superconductivity Research, University of Maryland, College Park, Maryland, United States, 3 Department of Physics and Astronomy, Rowan University, Glassboro, New Jersey, United States
Show AbstractT4/W4: Joint Session: Capacitors
Session Chairs
Tuesday PM, November 28, 2006
Room 302 (Hynes)
11:45 AM - **T4.5/W4.5
Ferroelectric/electrode Interface: ab initio Description and Impact on the Film Properties.
Alexander Tagantsev 1 , Guido Gerra 1 , Nava Setter 1
1 IMX Ceramics Laboratory, Swiss Federal Institute of Technology (EPFL), Lausanne Switzerland
Show AbstractExperimental studies of ferroelectrics have provided ample evidence for the impact of the ferroelectric/electrode interface on different properties of ferroelectric capacitors. As theoretically demonstrated, it is this impact that can shift the transition temperature of ferroelectric thin films or impede the transition itself [1-4], smear anomalies (e.g., the singularity of the dielectric permittivity) associated with the phase transition [5,6], and promote ferroelectric switching[7]. However, despite an appreciable progress in the theoretical description of the impact of ferroelectric/electrode coupling on the properties of ferroelectric films, one is to face serious problems concerning the practical use of the results obtained. First, most of the results have been obtained in terms of the continuous Landau-Ginsburg phenomenological framework which has been used at spatial scales which are too small to justify its applicability. Second, the few relevant results of first principles calculations have been obtained for systems which are too small to be (at least presently) of practical interest.In this paper, first, we present the results of our ab initio theoretical treatment of the BaTi03/SrRu03 interface and of its impact on the ferroelectric properties of ultrathin ferroelectric thin films. Specifically, we demonstrate that in the case of metal-oxide electrodes a new mechanism of ferroelectric-polarization screening is possible. Within this mechanism, due to the ionic polar