Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session L17: Focus Session: Magnetic Oxide Thin Films - Ferroic and Oxide Tunnel Junctions |
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Sponsoring Units: GMAG DMP Chair: James Eckstein, University of Illinois at Urbana-Champaign Room: D174 |
Tuesday, March 22, 2011 2:30PM - 3:06PM |
L17.00001: All-Manganite Tunnel Junctions with Interface-Induced Barrier Magnetism Invited Speaker: The recent discovery of several unexpected phases at complex oxide interfaces is providing new insights into the physics of strongly correlated electron systems. The possibility of tailoring the electronic structure of such interfaces has triggered a great technological drive to functionalize them into devices. In this communication, we describe an alternative strategy to produce spin filtering by inducing a ferromagnetic insulating state in an ultrathin antiferromagnetic layer in contact with a ferromagnetic layer. This artificially induced spin filtering persists up to relatively high temperatures and operates at high applied bias voltages. The results suggest that after playing a key role in exchange-bias for spin-valves, uncompensated moments at engineered antiferromagnetic interfaces represent a novel route for generating highly spin-polarized currents with antiferromagnets.\\[4pt] Work done in collaboration with M. Bibes, C. Carr\'{e}t\'{e}ro, A. Barth\'{e}l\'{e}my (Unit\'{e} Mixte de Physique CNRS/Thales, Campus de Polytechnique, 1, Avenue A. Fresnel, 91767 Palaiseau (France) and Universit\'{e} Paris-Sud, 91045 Orsay (France)), F.A. Cuellar, C. Visani, A. Rivera-Calzada, , C. Le\'{o}n, J. Santamaria (Grupo de F\'{\i}sica de Materiales Complejos, Universidad Complutense de Madrid, 28040 Madrid (Spain)), M.J. Calder\'{o}n, L. Brey (Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid (Spain)), K. March, M. Walls, D. Imhoff (Laboratoire de Physique des Solides, CNRS, Universit\'{e} Paris-Sud, 91405 Orsay (France)), R. Lopez Anton, T.R. Charlton (ISIS, Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX (United Kingdom)), E. Iborra (Universidad Polit\'{e}cnica de Madrid, Escuela T\'{e}cnica Superior de Ingenieros de Telecomunicaciones, 28040 Madrid ( Spain)), F. Ott (L\'{e}on Brillouin, CEA/CNRS, UMR 12, 91191 Gif-sur-Yvette (France)). [Preview Abstract] |
Tuesday, March 22, 2011 3:06PM - 3:18PM |
L17.00002: Nanostructured CoFe$_{2}$O$_{4}$ Films for Magnetic Logic Applications Ryan Comes, Man Gu, Mikhail Khokhlov, Jiwei Lu, Stuart Wolf CoFe$_{2}$O$_{4}$ (CFO) offers unique properties as a magnetoelectric material due to its large magnetoelastic response when strained. Previous work has shown that when CFO is co-deposited with BiFeO$_{3}$ (BFO) nanostructured phase segregation occurs and electrical control of the magnetic anisotropy is possible [1]. Such a system offers unique possibilities for an electrically-controlled spintronic logic scheme. To that end, CFO films were grown on MgO and SrTiO$_{3}$ (STO) substrates using pulsed electron deposition. Films grown on MgO substrates exhibit large perpendicular anisotropy due to epitaxial strain, while films on STO exhibit mixed anisotropy. Using electron-beam lithography, nanopillars were etched into the film in dense arrays and characterized using magnetic force microscopy. Pillar arrays were produced with diameters between 30 and 75 nm with pitch ranging from 90 to 200 nm. The dipole interactions in these pillars were examined and their potential applications for spintronic logic were evaluated. Thinner CoFe$_{2}$O$_{4}$ islands were also patterned on STO with EBL and then used as a template for a co-deposited BFO/CFO film. Results of this work will also be presented. \\[4pt] [1] Zavaliche, F., et al. \textit{Nano Lett.}, 2007, 7 (6), pp 1586--1590 [Preview Abstract] |
Tuesday, March 22, 2011 3:18PM - 3:30PM |
L17.00003: Spin-polarized tunnelling across single or double ferrite-based spin-filters Sylvia Matzen, Jean-Baptiste Moussy, Richard Mattana, Karim Bouzehouane, Cyrile Deranlot, Frederic Petroff, Jagadeesh Moodera, Guoxing Miao The generation of highly spin-polarized electron currents at room temperature is the basis of most spin-based device technologies. One approach known as spin filtering, has the potential of generating 100{\%} spin-polarized currents by the spin selective transport of electrons across a ferromagnetic tunnel barrier. In this work, we investigate the spin-polarized tunnelling characteristics of ferrites (CoFe2O4, NiFe2O4 and MnFe2O4), which are exciting candidates for spin filtering at room temperature. Tunnel junctions containing epitaxial ferrite tunnel barriers have been grown by oxygen plasma-assisted molecular beam epitaxy. Their structural, chemical and magnetic properties having previously been optimized by a number of in situ and ex situ methods, we focus on the spin-polarized tunnelling in the ferrite-based systems using different measurement techniques and we propose an unconventional device combining two ferrite magnetic tunnel barriers in order to get large tunnelling magnetoresistance without the necessity of magnetic electrodes. [Preview Abstract] |
Tuesday, March 22, 2011 3:30PM - 3:42PM |
L17.00004: Effect of Strain on Electronic and Magnetic Structure of Fe-doped CoFe$_{2}$O$_{4}$ Jarrett Moyer, Carlos Vaz, Ezana Negusse, Dario Arena, Victor Henrich The development of new materials with large room temperature spin polarizations and small conductivity mismatches with semiconductors is key for more complex spintronics devices. CoFe$_{2}$O$_{4}$ has a high Curie temperature (T$_{C}$ = 793 K), a large predicted spin polarization, and, when doped with iron, a conductivity similar to semiconductors; however, the magnetic properties of thin films are different from the bulk. To investigate the effect of strain, Co$_{1-x}$Fe$_{2+x}$O$_{4}$ thin films (0 $\le x\le $ 0.65) are grown epitaxially on MgO (001) and SrTiO$_{3}$ (001) by MBE. UPS probes filled valence band states, while X-ray Linear Dichroism (XLD) determines d-orbital occupations. SQUID magnetometry and XMCD are used to determine bulk and site-specific magnetic moments, respectively. These measurements allow us to understand how strain affects the electronic and magnetic structure of Co$_{1-x}$Fe$_{2+x}$O$_{4}$ thin films. [Preview Abstract] |
Tuesday, March 22, 2011 3:42PM - 3:54PM |
L17.00005: Fabrication and properties of LuFe2O4 thin film Wenbin Wang, Xiaoshan Xu, Zheng Gai, Paul C. Snijders, Thomas Z. Ward, Jian Shen We have succeed in growing the LuFe2O4 polycrystalline thin film on the MgO(111) substrate with the Pulsed laser deposition(PLD) method. The surface structures, crystallographic and magnetic properties of the sample were characterized by XRD, AFM, SEM and SQUID. XRD pattern shows the sample crystallized in both (001) and (110) directions, which is also reflected in their morphological appearance in both AFM and SEM images. SQUID measurements reveal strong ferromagnetic signal in the thin film. [Preview Abstract] |
Tuesday, March 22, 2011 3:54PM - 4:06PM |
L17.00006: Magnetic Force Microscopy of Magnetite Thin Films with Transition Metal Buffer Layers Alfred KH. Lee, Mark C. Monti, John T. Markert, Alex de Lozanne, Priyanga B. Jayathilaka, Chris A. Bauer, Casey W. Miller Magnetite (Fe$_{3}$O$_{4}$) has been the subject of interest as a material for use in spin devices. Its ideal properties for this application break down in thin film morphologies due to the occurrence of antiphase boundaries (APBs). The density of APBs can be adjusted to some degree via film strain. This is accomplished in this work by including a variety of transition metal buffer layers between Fe$_{3}$O$_{4}$ and its MgO substrate. We investigate the microscale magnetic domain structure via magnetic force microscopy of Fe$_{3}$O$_{4}$ films on MgO with no, a Mo, or an Fe buffer layer across a temperature range surrounding the Verwey temperature (T$_V \sim$ 120K) and compare to bulk measurements from a SQUID magnetometer. [Preview Abstract] |
Tuesday, March 22, 2011 4:06PM - 4:18PM |
L17.00007: A structural, electronic and magnetic study of ultrathin iron oxides M. Monti, B. Santos, J. Marco, J. de la Figuera, M.A. Ni\~no, T.O. Mente\c{s}, A. Locatelli, K.F. McCarty, A. Mascaraque, O. Rodr\'Iguez de la Fuente Iron oxides continue to fascinate us after nearly a century of ``modern'' science devoted to their growth, properties and structure. Recently, a revival of research has been spurred by the multiferroic character of magnetite, and by its predicted half-metal character, both interesting for spintronic applications. Maghemite is, on the other hand, an interesting counterpart to magnetite. They both present the same inverse spinel structure but maghemite is a ferrimagnetic insulator. In this work we individually characterize flat triangular islands, less than 10 atomic layers thick, of magnetite and maghemite on Ru(0001) by means of selected-area X-ray photoemission and absorption, X-ray circular dichroism and low-energy electron diffraction and reflectivity. We grow magnetite islands in-situ, with well-defined magnetic domains inside, surrounded by a w\"{u}stite wetting layer by depositing iron in a molecular oxygen background pressure. Further exposure to NO$_{2}$ transforms the magnetite islands into maghemite, while changing the w\"{u}stite wetting layer into hematite. [Preview Abstract] |
Tuesday, March 22, 2011 4:18PM - 4:54PM |
L17.00008: Giant tunnel electroresistance and electrical control of spin polarization with ferroelectric tunnel barriers Invited Speaker: At room temperature, we use piezoresponse force microscopy to show robust ferroelectricity in BaTiO$_{3}$ ultrathin films, and conductive-tip atomic force microscopy to demonstrate the resistive readout of the polarization state via its influence on the tunnel current [1]. This giant electroresistance nondestructive readout paves the way for ferroelectric memories with simplified architectures, higher densities and faster operation. Additionally, ferroelectric tunnel junctions with ferromagnetic electrodes were engineered to demonstrate local, large and non-volatile control of carrier spin polarization by switching ferroelectric polarization [2]. Our results represent a giant interfacial type of magnetoelectric coupling and suggest a new low-power approach for spin-based information control. \\[4pt] [1] V. Garcia \textit{et al.}, Nature 460, 81 (2009) \\[0pt] [2] V. Garcia \textit{et al.}, Science 327, 1106 (2010) [Preview Abstract] |
Tuesday, March 22, 2011 4:54PM - 5:06PM |
L17.00009: Electrically Controlled Spin Valve at a Complex Oxide Interface Evgeny Tsymbal, J.D. Burton Since the discovery of giant magnetoresistance exploration of spin-dependent electronic transport has proved promising for applications. To avoid the costly generation of magnetic fields in these devices there have been recent efforts toward manipulating magnetization by \textit{electric} fields. Such magnetoelectric effects can be induced at the surfaces and interfaces of many ferromagnetic metals. Ferroelectric materials are especially helpful in this because their spontaneous electrical polarization can induce a large response at the interface with a magnetic metal. One example is the ferroelectric control of magnetic order at the interface between La$_{1-x}A_{x}$MnO$_{3}$ (where $A$ is a divalent cation), and the ferroelectric BaTiO$_{3}$ [1]. Importantly, ferroelectric films can now be made thin enough (less than a few nm) to allow measurable electron tunneling while still maintaining a stable and switchable polarization [2]. Here we show that those few atomic layers near the interface sensitive to the ferroelectric polarization can act as an atomic scale spin-valve in series with the ferroelectric tunnel barrier. Switching the ferroelectric barrier induces more than an order of magnitude change in the conductance due to the interfacial spin-valve, constituting a substantial spin-dependent transport phenomenon controlled by an electric field alone.\\[0pt] [1] J. D. Burton and E. Y. Tsymbal, Phys. Rev. B \textbf{80}, 174406 (2009).\\[0pt] [2] A. Gruverman\textit{ et al.}, Nano Lett. \textbf{9}, 3539 (2009). [Preview Abstract] |
Tuesday, March 22, 2011 5:06PM - 5:18PM |
L17.00010: Magnetic state switching controlled by a voltage in La$_{0.7}$Ca$_{0.3}$MnO$_{3}$/(Ba, Sr)TiO$_{3}$/La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ tunneling junctions Weijin Hu, Ke Chen, Xiaoxing Xi, Qi Li, Zhidong Zhang We report the switching of the two magnetic states (parallel and antiparallel states) in La$_{0.7}$Ca$_{0.3}$MnO$_{3}$/(Ba, Sr)TiO$_{3}$/La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ magnetic tunneling junctions by measuring the tunneling magnetoresistance after applying a voltage pulse. The junction size ranges between 5x5 to 20x20 $\mu $m$^{2}$ with the barrier thickness in the range of 1-3 nm. We have found that magnetic state of the junction can be switched both from the antiparallel to parallel state and from the parallel to antiparallel state in certain and different field ranges, respectively. The switching does not depend on the polarity of the electrical field direction and the magnetic field direction. The critical voltage for the switching depends on the magnetic field with higher voltage needed for lower magnetic field. The critical voltage depends almost linearly on the bias magnetic field when the switch occurs. [Preview Abstract] |
Tuesday, March 22, 2011 5:18PM - 5:30PM |
L17.00011: Four resistance states in La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/(Ba, Sr)TiO$_{3}$/La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ multiferroic tunnel junction at room temperature Peng Xu, Yuewei Yin, Weijin Hu, Muralikrishna Raju, Qi Li, Xiaoguang Li Multiferroic tunnel junction (MFTJ), composed of two ferromagnetic electrodes separated by a thin ferroelectric barrier, has been predicted to serve as a four-state device as a result of the coexistence of tunneling magnetoresistance and tunneling electroresistance effects. Our previous results have demonstrated such devices, but only at low temperatures. Here, we report a MFTJ composed of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/(Ba, Sr)TiO$_{3}$/La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ fabricated by pulsed-laser deposition. A typical R-H loop with a sharp-switched resistance states (magnetic parallel and antiparallel) similar to that of magnetic tunnel junctions has been observed up to room temperature. Upon polarization reversal of the barrier, both the parallel and antiparallel resistances will switch to a different value. Clear tunneling magnetoresistance and tunneling electroresistance, hence the four-resistance states, have been observed at room temperature. The resistance states can be switched between them by electric and magnetic fields and the manipulation of the states will be discussed. [Preview Abstract] |
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