Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session V38: Focus Session: Multiferroics and Multiferroic Composites |
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Sponsoring Units: DCMP Chair: Claude Ederer, Trinity College, Ireland Room: Morial Convention Center 230 |
Thursday, March 13, 2008 11:15AM - 11:51AM |
V38.00001: In pursuit of strongly coupled multiferroic oxides Invited Speaker: The rational design of new materials with emergent properties is a riveting challenge today in materials physics. It begins with understanding a mechanism to control the interplay between diverse microscopic degrees of freedom in order to create targeted macroscopic phenomena and ends with the discovery or design of new material realizations. When combined with first-principles density-functional theory, this approach provides an efficient strategy to survey the vast space of possible materials to target for synthesis. In this talk I will discuss our recently proposed strategies to identify new multiferroics oxides in which magnetism not only coexists with but also is strongly coupled to ferroelectricity. In one case the interplay of spins, optical phonons, and strain leads to a competition between different ordered states producing a colossal magnetoelectric effect. In a second case, a ferroelectric distortion can be designed to induce weak-ferromagnetism facilitating the electric-field control of a switchable magnetization. We also present first-principles density-functional calculations for several potential realizations. [Preview Abstract] |
Thursday, March 13, 2008 11:51AM - 12:03PM |
V38.00002: Growth and characterization of YMnO$_{3}$ nanocrystalline prisms E. Ramos-Moore, Cameron Keenan, Sandeep Chandril, A. L. Cabrera, Thomas H. Myers, David Lederman YMnO$_{3}$ epitaxial self-assembled nanoprisms were grown on GaN by molecular beam epitaxy. The prisms formed suddenly after 6 unit cells during Stranski-Krastanow epitaxial growth at 850 $^{o}$C, with sizes ranging from 20 nm to 60 nm in height and 50 nm to 500 nm in lateral dimensions. They were characterized via energy dispersive analysis of x-rays (EDAX) mapping and x-ray diffraction and reflectivity. EDAX line scans across the prisms showed that the prisms were composed of YMnO$_{3}$. X-ray diffraction showed a 2.2{\%} strain along the growth direction and a 1.6{\%} compression in the plane when compared to bulk lattice parameters. [Preview Abstract] |
Thursday, March 13, 2008 12:03PM - 12:15PM |
V38.00003: Properties of YMnO3 Self-assembled Nanocrystalline Prisms on GaN Cameron Keenan, Sandeep Chandril, Thomas H. Myers, David Lederman, Esteban Ramos-Moore, Alejandro L. Cabrera The high-temperature (850 $^{\circ}$C) molecular beam epitaxy deposition of YMnO$_{3}$ on HVPE GaN(0001) resulted in the spontaneous formation of YMnO$_{3}$ nanoprism structures due to Stranski-Krastanow growth mode. Their dimensions ranged from 20 nm to 60 nm in thickness and 50 nm to 500 nm in lateral size. The local dielectric properties of the sample were investigated using scanning surface potential microscopy (SSPM). Remanent hysteresis loops were used to compare the switching properties of the nanoprisms and underlying film. A larger remanence was observed for the prisms, most probably due to the lack of surrounding film areas that would clamp the ferroelectric response. As a result, the remanent polarization increased roughly linearly with increasing prism surface area. [Preview Abstract] |
Thursday, March 13, 2008 12:15PM - 12:27PM |
V38.00004: Epitaxial growth and electrical properties of {\it perovskite} HoMnO$_{3}$ thin films Daisuke Kan, M. Murakami, W. Yu, R.L. Greene, S.W. Cheong, I. Takeuchi Recently, it was predicted that orthorhombic HoMnO$_{3}$ would exhibit relatively large polarization (of the order of $\mu$C/cm$^ {2}$) due to the existence of a ferroelectric order in the {\it E}- type magnetic structure [1]. We have fabricated perovskite HoMnO$_{3}$ thin films on SrTiO$_{3}$ (001) substrates by pulsed laser deposition. X-ray 2$\theta$-$\theta$ scan shows (00 {\it l}) peaks only indicating that there are no secondary phases. The reciprocal space mapping around the SrTiO$_{3}$ (103) Bragg reflection and the $\phi$ scan of the HoMnO$_{3}$ (103) peak reveals the tetragonal symmetry of the films and the epitaxial relationship, [100]HoMnO$_{3}$ // [100]SrTiO$_{3}$ and [001] HoMnO$_{3}$ // [001]SrTiO$_{3}$, confirming that the film has the perovskite structure and not the hexagonal one. The films show good insulating properties at low temperatures. We will present electrical properties of the films including results of PUND measurements in applied magnetic field below the Neel temperature. This work is supported by NSF MRSEC, ARO, and the W. M. Keck Foundation. \newline [1] Sergienko et al., PRL 97, 227204 (2006). [Preview Abstract] |
Thursday, March 13, 2008 12:27PM - 12:39PM |
V38.00005: Magnetic ground state of PbVO$_{3}$ and origin of the large tetragonal distortion Kengo Oka, Ikuya Yamada, Masaki Azuma, Mikio Takano, Yuichi Shimakawa, Soshi Takeshita, Kohki H. Satoh, Akihiro Koda, Ryosuke Kadono, Hiroshi Kojitani, Masaki Akaogi Magnetic property of PbTiO$_{3}$-type perovskite PbVO$_{3}$ with a large tetragonal distortion ($c/a$ = 1.23)$^{1}$ was investigated. Long-range antiferromagnetic ordering with $T_{N}$ = 45 K was found by a $\mu $SR measurement. Magnetic susceptibility of multi domain crystal showed a broad maximum centered at 180 K indicated the 2-dimensional nature in magnetism. This is consistent with the $d_{xy}$ orbital ordering predicted by the band calculation.$^{2}$ We propose a mechanism that the pyramidal coordination with a short vanadium-apical oxygen bond is stabilized to lift the orbital degeneracy in this $d^{1}$ system. Accordingly, PbMnO$_{3}$ (Mn$^{4+}$, $d^{3})$ newly stabilized at 15 GPa has a pseudo cubic structure like PbCrO$_{3}$. This scenario explains the pressure induced tetragonal to cubic, insulator to metal transition$^{1}$ of PbVO$_{3}$ and similar large tetragonal distortion of BiCoO$_{3}$. [1]A. A. Belik, \textit{et al., Chem. Mater.}, \textbf{18} (2006) 798. [2]Y. Uratani, \textit{et al.}, \textit{Jpn. J. Appl. Phys.}, \textbf{44} (2005) 7130. [Preview Abstract] |
Thursday, March 13, 2008 12:39PM - 12:51PM |
V38.00006: A one-cent room-temperature magnetoelectric sensor Casey Israel, Neil Mathur, James Scott The replacement of silver-palladium with nickel as an electrode material is reducing the cost of industrially manufactured barium titanate based multilayer capacitors, but nickel is magnetic. We discuss direct magnetoelectric coupling at room temperature in these one-cent multilayer capacitors, the influence of the multilayer geometry on this strain-mediated coupling, and why these capacitors might be adopted as cheap magnetic-field sensors that do not require an electrical power source. [Preview Abstract] |
Thursday, March 13, 2008 12:51PM - 1:03PM |
V38.00007: Inversion symmetry controlled multiferroic response in an Ising Chain Magnet YounJung Jo, SeongSu Lee, HeeTaek Yi, SangWook Cheong, Luis Balicas Recently, Choi et al. [1] discovered that ferroelectricity in the Ising chain magnet results from inversion symmetry breaking due to the formation of an alternating ionic order of two different ions leading to an up-up-down-down spin configuration. Here we report the observation of drastic changes in the multiferroic character as a function of magnetic field in the Ising chain magnet. Application of a magnetic field up to 33 T, leads to two abrupt changes in the dielectric constant, respectively at $H_1$ = 5 T and at $H_2$=20T, with the first one leading to a fast suppression of the dielectric polarization. The saturation values of the magnetic moment observed by using a vibrating sample magnetometer and a cantilever beam magnetometer suggest that the one ionic moments align along the field for fields above 5 T followed by the subsequent alignment of the other ionic moments above 20 T. [1] Y.J. Choi $et al.$ Physical Review Lett. submitted [Preview Abstract] |
Thursday, March 13, 2008 1:03PM - 1:15PM |
V38.00008: Inter-relationship among magnetization, polarization and magnetic wave vector in multiferroic spinel CoCr$_{2}$O$_{4}$ Young Jai Choi, Jun Okamoto, Di-Jing Huang, Kuo Sheng Chao, Hong-Ji Lin, Chien-Te Chen, Michel van Veenendaal, Thomas A. kaplan, Sang-Wook Cheong It has been known that the spinel CoCr$_{2}$O$_{4}$ is a multiferroic with conical spiral magnetic order characterized by three physical parameters: magnetization (\textbf{M}), polarization (\textbf{P}) and magnetic modulation vector (\textbf{Q}). We have found that these observables have a close inter-relationship in the multiferroic state and their inter-relationship changes in a methodical manner upon temperature variation and through applied magnetic fields. In order to understand the origin of this inter-relationship, we have performed comprehensive characterization experiments on the multiferroic compound, including measurements of dielectric constant, polarization, specific heat, magnetic susceptibility, and resonant x-ray scattering as functions of temperature and applied magnetic field. [Preview Abstract] |
Thursday, March 13, 2008 1:15PM - 1:27PM |
V38.00009: Structural and Dielectric Properties of CoFe$_{2}$O$_{4}$-Ba$_{0.90}$La$_{0.067}$Ti$_{0.91}$Zr$_{0.09}$O$_{3}$ composite thin films. Eduardo Delgado, Carlos Ostos, Maria Martinez, Lourdes Mestres, David Lederman, Pedro Prieto CoFe$_{2}$O$_{4}$-Ba$_{0.90}$La$_{0.067}$Ti$_{0.91}$Zr$_{0.09}$O$_{3 }$(CFO-BLZT) composite thin films were grown via RF oxygen magnetron sputtering from a CFO-BLZT mixed target on electrically-conducting single-crystal Nb-doped SrTiO$_{3}$ (100) substrates at 1033 K. From scanning electron microscopy coupled with energy dispersive analysis of x-rays we determined that the CFO and BLZT were phase separated. X-ray photoemission spectroscopy showed that the TiO$_{6}$ octahedron in the perovskite structure was modified by the lanthanide incorporation. The dielectric characterization showed that the samples were ferroelectric at room temperature. The ferroelectric hysteresis loops measured as a function of magnetic field showed that these samples are multiferroic. [Preview Abstract] |
Thursday, March 13, 2008 1:27PM - 1:39PM |
V38.00010: Studies of Magnetoelectric properties in (1-x)Pb(Fe$_{2/3}$W$_{1/3})$O$_{3}$-xPbTiO$_{3}$ solid solutions thin films Ashok Kumar, Ram Katiyar We have fabricated (1-x)Pb(Fe$_{2/3}$W$_{1/3})$O$_{3}$-xPbTiO$_{3}$ (PFWT) (x=0.50) thin films on Pt/Si substrates using sol-gel technique. The XRD patterns revealed a single-phase nature of the compound. The microstructure and surface morphology were investigated using SEM and AFM techniques that indicated good homogeneity and had surface roughness of 10-15 nm with particle size of $\sim $ 30-50 nm. The dielectric relaxation studies in these films were carried out measured in the temperature range of 100K-650K and the frequency range of 100Hz-1MHz. Raman and dielectric data indicate that the crystal structure changes from tetragonal to cubic i.e. a ferroelectric phase transition at 575K. The dielectric properties of PFWT thin films were studied in the temperature range 80-600 K over a wide range of frequencies. The slope of the reciprocal of the dielectric constant is 2:1, matched well with the simplest Landau free energy model and it indicates continuous second order displacive ferroelectric phase transition. The polarization hysteresis curve at room temperature illustrated a ferroelectric nature. The detailed of magnetic and magneto electric properties with of PFWT will be discussed. [Preview Abstract] |
Thursday, March 13, 2008 1:39PM - 1:51PM |
V38.00011: Magnetoelectric Effects in hexagonal ferrite-PZT bilayers V.M. Mathe, G. Srinivasan Magnetoelectric (ME) bilayers consisting of magnetostrictive and a piezoelectric layer are of interest for studies on the nature of ME interactions and useful technologies. Co$_{2}$Z and Zn$_{2}$Y are well known hexagonal ferrites with easy plane or uniaxial anisotropy. PZT has high piezoelectric coefficient. This study is on samples with Co$_{2}$Z or Zn$_{2}$Y as a magnetostrictive layer and PZT as a piezoelectric layer to form magnetoelectric bilayers. Low frequency (100 Hz) ME coefficient was measured over 0-17 kOe for various orientations of bilayers in a plane parallel to ac and bias magnetic fields. We measured a strong dependence of the ME voltage coefficients on magneitude and orientation of the bias field. The data are compared with theory. VLM gratefully acknowledge the award of a BOYSCAST fellowship and a FAST TRACK fellowship by DST, India. The research was supported by NSF grants. [Preview Abstract] |
Thursday, March 13, 2008 1:51PM - 2:03PM |
V38.00012: Magnetic properties in multiferroic Fe/BaTiO$_{3}$/SrTiO$_{3}$(001) M. Pechan, C. Yu, S. Srivastava, C. Palmstr{\O}m, M. Biegaslski, C. Brooks, D. Schlom Fe (001) films (30 nm) have been epitaxially grown on ferroelectric BaTiO$_{3}$/SrTiO$_{3}$(001) to study the interaction between the multiferroic components. We report the magnetic properties as a precursor to a full investigation of the multiferroic interactions. Ferromagnetic resonance measurements were carried out at 36 GHz cavity and variable frequency microstrip resonators. Four-fold anisotropy is present in these Fe (001) films with energy density $\sim $1.3x10$^{5}$ erg/cm$^{3}$, consistent with bulk Fe values and indicating high quality Fe grown on the ferroelectric. Also present is a small, additional resonance peak, with large out-of-plane uniaxial anisotropy [$\sim $0.75*(2$\pi $M$^{2})$] attributed to strained Fe at the interface, although structural data shows the majority of the film is relaxed. This interfacial Fe will likely provide the desired coupling between the ferromagnetic and ferroelectric components in the system. Frequency/field in-plane dispersion curves further confirm the high quality of the Fe films in these samples. [Preview Abstract] |
Thursday, March 13, 2008 2:03PM - 2:15PM |
V38.00013: Dynamic observation of magnetoelectric coupling effect using magnetic force microscopy and Lorentz TEM Sung Hwan Lim, Todd Brintlinger, Daisuke Kan, Yi Qi, John Cumings, Ichiro Takeuchi, Lourdes Salamanca-Riba Dynamic observation of the strain mediated magnetoelectric (ME) coupling effect was pursued by applying an external electric (E) field to a Fe$_{0.7}$Ga$_{0.3}$/BaTiO$_{3 }$(FeGa/BTO) TEM sample in the Lorentz imaging mode in a TEM. An epitaxial piezoelectric BTO layer followed by a polycrystalline magnetostrictive FeGa layer were synthesized by pulsed laser deposition and magnetron sputtering, respectively. The BTO film had Ps = 17 $\mu $C/cm$^{2 }$measured using SrRuO$_{3}$ (bottom) and FeGa (top) electrodes. The FeGa film showed strong magnetic anisotropy with in-plane easy axis. To apply an E field in-plane, FeGa was patterned on BTO using e-beam lithography. The change of magnetic domain structure was observed under an applied magnetic field in TEM. The ME effect was also investigated using MFM. After applying an E field (100 kV/cm) on the BTO layer, a reorientation of the magnetic moments in the FeGa layer along the E field direction was observed. [Preview Abstract] |
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