Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session L13: Focus Session: Interfacial Ordering |
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Sponsoring Units: DMP Chair: Charles Ahn, Yale University Room: Colorado Convention Center Korbel 4C |
Tuesday, March 6, 2007 2:30PM - 2:42PM |
L13.00001: Atomic resolution spectroscopic imaging of electronic phenomena in oxide interfaces M. Varela, H. M. Christen, H. N. Lee, D. H. Kim, L. Petit, T. C. Schulthess, J. Tao, A. R. Lupini, S. J. Pennycook, W. Luo, S. T. Pantelides, J. Garcia-Barriocanal, C. Leon, J. Santamaria Electron energy loss spectroscopy in the STEM is a powerful tool to study the structure, chemistry and electronic properties of oxides with atomic resolution, in real space. In perovskites the O 2p bands and the transition metal 3d bands are very close to the Fermi level so the electronic properties can be probed by studying the fine structure on the O K edge and the transition metal L edge. Column-by-column EELS reveals direct information about the unique phenomena going on in oxide interfaces. For example, in superconducting/ferromagnetic YBa$_{2}$Cu$_{3}$O$_{7}$/ La$_{0.3}$Ca$_{0.7}$MnO$_{3}$ superlattices significant transfer of electrons from the manganite into the superconductor is found over nanometric length scales. But quite different phenomena occur in other manganite interfaces such as LaMnO$_{3}$/SrTiO$_{3}$. In this talk both experiments and first principles calculations with simulations of the ELNES will be discussed. Sponsored by the Office of Basic Energy Sciences, Div of Materials Sciences and Engineering, US DOE under contract DE-AC05-00OR22725 with ORNL managed by UT-Battelle LLC, by the ORNL LDRD Program and by the ORNL-ORISE Postdoctoral Program. [Preview Abstract] |
Tuesday, March 6, 2007 2:42PM - 2:54PM |
L13.00002: Magnetic and electronic properties of complex oxide interfaces Weidong Luo, Maria Varela, Stephen J. Pennycook, Sokrates T. Pantelides Interfaces between two complex materials based on perovskite oxides can have novel physical properties. We studied the magnetic and electronic properties of La$_{0.67}$Ca$_{0.33} $MnO$_3$/YBa$_2$Cu$_3$O$_7$ (LCMO/YBCO) superlattices using first-principles density-functional theory (DFT). The energetics of several types of magnetic (spin) configurations of Mn ions near the LCMO/YBCO interface have been calculated using the DFT approach. Their magnetic and electronic properties have been explored and compared to the properties of bulk materials. These results are compared to recent experimental observation of suppressed magnetization at the LCMO/YBCO interface. We will also discuss the possibility of charge transfer across the interface, as suggested by recent experimental results from local electron energy-loss spectroscopy (EELS). This research was sponsored by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. Department of Energy, under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC, and by the McMinn Endowment at Vanderbilt University. [Preview Abstract] |
Tuesday, March 6, 2007 2:54PM - 3:06PM |
L13.00003: Modified doping at cuprate / lanthanum manganite interfaces Jacobo Santamaria, J. Garcia Barriocanal, A. Rivera, C. Leon, M. Varela, S.J. Pennycook, Z. Sefrioui Oxide heterostructures allow combining materials with similar structure but with very different ground states, which may compete at the interface to yield novel behaviors and functionalities. We explore the YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) / La$_{1-x}$Ca$_{x}$MnO$_{3}$ (LCMO) interface in thin film heterostructures. For x=0.3 the manganite is ferromagnetic which causes a strong depression of the superconductivity at the YBCO side. There is also a depression of the ferromagnetic moment at the interface suggesting electron transfer from the manganite into the YBCO. This is confirmed from superlattices alternating YBCO and LaMnO$_{3}$ (LMO), an A- type AF insulator. While for thin LMO layers ($<$ 6 unit cells) there is little effect on YBCO superconductivity, thicker LMO layers result in reduced Tc values and induced ferromagnetism at the interface, thus providing a firm indication of charge transfer. The occurrence of charge transfer over length scales much longer than the Thomas Fermi screening length (1 nm) is a novel behavior which, we hope, will stimulate future theoretical studies. Work supported by CICYT MAT2005 06024 C02-02. [Preview Abstract] |
Tuesday, March 6, 2007 3:06PM - 3:18PM |
L13.00004: Interaction between magnetism and superconductivity in $La_{0.7}Ca_{0.3}MnO_3$/$YBa_2Cu_3O_{7-\delta}$ multilayers T. Hu, H. Xiao, C. C. Almasan, C. Visani, Z. Sefrioui, J. Santamaria Angular dependent resistivity measurements were performed on $La_{0.7}Ca_{0.3}MnO_3$/$YBa_2Cu_3O_{7-\delta}$ (LCMO/YBCO) heterostructures below and above the superconducting transition temperature $T_c \approx$ 90 K in different applied magnetic field. Besides the conventional intrinsic anisotropic magnetoresistance (AMR) present above $T_c$, we observe another anisotropic magnetoresistance, which only arises below $T_c$ and increases significantly with decreasing temperature. Also, the proximity-induced resistance, which appears in the LCMO layer, displays a spectacular increase at $T_c$ and then decreases significantly with decreasing temperature, persisting down to the lowest measured T of 72 K. This anomalous AMR and the proximity-induced resistance in the LCMO layer could be due to the triplet component of the superconducting condensation which penetrates into the ferromagnet over a long distance. [Preview Abstract] |
Tuesday, March 6, 2007 3:18PM - 3:30PM |
L13.00005: Magnetic anisotropy and vortex dynamics in LCMO/YBCO heterostructures H. Srikanth, N.A. Frey, C. Visani, J. Santamaria Interplay of ferromagnetism and superconductivity in heterostructures of highly spin polarized CMR oxides and cuprate superconductors, is of topical interest. We have used a sensitive radio-frequency (RF) resonant method based on a tunnel-diode oscillator (TDO) to simultaneously probe the dynamic magnetic susceptibility and the vortex penetration depth in well characterized sputtered bi-layers (LCMO/YBCO) and tri-layers (LCMO/YBCO/LCMO), grown on STO substrates with the thickness of LCMO and YBCO being 40 u.c. and 15 u.c., respectively. Transverse susceptibility in the normal state shows distinct peaks associated with the anisotropy fields in LCMO. In the superconducting state, complex coupled response is observed with the region just below T$_{c}$ dominated by flux flow in a vortex liquid state. Experimental results with various field orientations are reported and analyzed in the context of proximity effect, spin diffusion, flux penetration and dissipation in the presence of geometrical barriers. Overall, our work demonstrates the effectiveness of RF experiments in probing the magnetization and vortex dynamics in these systems. [Preview Abstract] |
Tuesday, March 6, 2007 3:30PM - 4:06PM |
L13.00006: Magnetism at the interface between ferromagnetic and superconducting oxides. Invited Speaker: Atomically controlled interfaces between two materials can give rise to novel physical phenomena and functionalities not exhibited by either of the constituent materials alone. Modern synthesis methods have yielded high-quality heterostructures of oxide materials with competing order parameters. Although magnetic correlations at the interface are expected to be important in determining the macroscopic properties of such nanosystems, a quantitative determination of the interfacial magnetic structure in oxides has thus far been very limited. Here we examine superlattices composed of the half-metallic ferromagnet La$_{2/3}$Ca$_{1/3}$MnO$_{3}$ and the high-temperature superconductor YBa$_{2}$Cu$_{3}$O$_{7}$ by core-level absorption spectroscopy with circularly polarized x-rays and by diffuse neutron reflectometry. The resulting data yield microscopic insight into the interplay of spin and orbital degrees of freedom at the interface. The data also reveal an extensive rearrangement of the magnetic domain structure at the superconducting transition temperature. The combination of techniques establishes an incisive probe of the interplay between competing electronic order parameters in oxide heterostructures. J. Chakhalian, J. W. Freeland, G. Srajer, J. Strempfer, G. Khaliullin, J.C. Cezar, T. Charlton, R. Dalgliesh, C. Bernhard, G. Cristiani, H.-U. Habermeier and B. Keimer, ``Magnetism at the interface between ferromagnetic and superconducting oxides,'' Nature Physics, v.2 , 244 (2006). [Preview Abstract] |
Tuesday, March 6, 2007 4:06PM - 4:18PM |
L13.00007: Interface Magnetic Order in LaFeO$_3$/LaCrO$_3$ and LaFeO$_3$/La$_{1-\delta}$MnO$_3$ Superlattices H.N. Lee, J.W. Freeland, G. Khaliullin, B. Keimer, J. Chakhalian Creation of sharp interfaces between strongly correlated electron systems can result in novel states at the boundary. Here we present our work using element-resolved x-ray probes to study the magnetic order in LaFeO$_3$(LFO)/LaCrO$_3$(LCO) and LaFeO$_3$/La$_{1-\delta}$MnO$_3$ superlattices. Using pulsed laser deposition with RHEED control, (111) and (100) oriented ultra-thin superlattices were grown with layer thicknesses of 1 to 9 unit cells. In the bulk LaFeO$_3$ and LaCrO$_3$ are antiferromagnetic while La$_{1-\delta}$MnO$_3$ is ferromagnetic. At the interface of (111) oriented LaFeO$_3$/La$_{1-\delta}$MnO$_3$ superlattices we find clear sign of large net magnetic moment on both Mn and Fe even at moderate fields. For the LFO/LCO case, the (111) case displays small net mangetic moment in both layers while the (100) orientated samples shows no clear sign of net magnetic moment even at fields up to 5T. Research sponsored by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy, under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC. [Preview Abstract] |
Tuesday, March 6, 2007 4:18PM - 4:30PM |
L13.00008: ABSTRACT WITHDRAWN |
Tuesday, March 6, 2007 4:30PM - 4:42PM |
L13.00009: Doping the interface of Mott-Insulator heterostructures Wei-Cheng Lee, Tami Pereg-Barnea, Allan MacDonald Recent rapid progress in techniques for layer-by-layer growth of transition metal oxides is making new types of heterostructures available. Previous studies have demonstrated interesting charge transfer and band bending effects near interfaces between Mott insulators and band insulators [1] and between polar and non-polar insulators [2]. We propose [3] interesting effects at several different classes of heterojunctions between ABO3 perovskites based on a single-band Hubbard model studied with several different approximate treatments of electron-electron interactions. Some potentially interesting material combinations will be discussed. \newline \newline [1] A. Ohtomo, etc., Nature 419, 378 (2002). \newline [2] N. Nakagawa, etc., Nature Materials 5, 204 (2006). \newline [3] W.-C. Lee and A.H. MacDonald, Phys. Rev. B 74, 075106 (2006) and work in preparation. [Preview Abstract] |
Tuesday, March 6, 2007 4:42PM - 4:54PM |
L13.00010: Polar Kerr effect of epitaxial magnetite thin films in the visible and near infrared spectral region Ji Cheng, George Sterbinsky, Bruce Wessels Magnetite thin films are of interest for spin polarized injection and magneto-electric devices. The polar magneto-optical Kerr effect (MOKE) and optical absorption were measured on epitaxial films over the visible and near infrared spectral region at room temperature. Magnetite thin films on magnesium oxide, strontium titanate, barium titanate and spinel substrates were deposited by molecular beam epitaxy using molecular oxygen and iron. A complex MOKE spectrum was measured over the spectral range of 1.5 to 3.0 eV. A negative transition was observed at 1.6 eV and a positive transition at 2.7 eV. These were previously attributed to intervalence charge transfer and intersublattice charge tranfer transitions. The detailed spectrum was dependent upon the substrate suggesting strain may be playing a role. Using MOKE magnetometry the coercive field was measured. The coercive field of the epitaxial film varied from 370 gauss for films deposited on MgO to 620 gauss for films deposited on barium titanate. [Preview Abstract] |
Tuesday, March 6, 2007 4:54PM - 5:06PM |
L13.00011: Epitaxial CoFe$_2$O$_4$(111)-based multilayers for spin filter applications Ana Ramos, Jean-Baptiste Moussy, Martine Gautier-Soyer Efficient spin filtering at room temperature has high potential for ultra sensitive detectors and spin injection into semiconductors, leading to the growth of spin-based devices. We investigate the interaction of spin filter CoFe$_2$O$_4$(111) epitaxial tunnel barriers with Co and Fe$_3$O$_4$ electrodes in light of their possible application at room temperature. The question of the exchange coupling that often prohibits the independent switching between a magnetic tunnel barrier and its magnetic electrode is addressed, as is the difference between an oxide/metal and oxide/oxide system. Our study of the magnetic reversal in the CoFe$_2$O$_4$/Co and CoFe$_2$O$_4$/Fe$_3$O$_4$ bilayers, supported by a detailed structural and chemical analysis of the samples and their interfaces, clearly evidences the effect of a metallic or an oxide interface. An unusual exchange spring magnet behavior arises in the case of the CoFe$_2$O$_4$/Fe$_3$O$_4$ samples due to the superexchange interactions found in these ferrimagnetic oxides. This unique exchange phenomenon at the oxide-oxide interface ultimately leads to a barrier/electrode system that switches independently without the necessity of a non-magnetic spacer. [Preview Abstract] |
Tuesday, March 6, 2007 5:06PM - 5:18PM |
L13.00012: Electron leakage and double-exchange ferromagnetism at a prototype metal-insulator interface: CaRuO$_3$/CaMnO$_3$ Sashi Satpathy, Birabar Nanda Density-functional studies of the electronic structure of a prototype interface between a paramagnetic metal and an antiferromagnetic insulator (CaRuO$_3$/ CaMnO$_3$) reveal how magnetism near the interface can be modified by the leaked electrons from the metallic to the insulating side. These electrons mediate a ferromagnetic interaction between the interface Mn moments via Anderson-Hasegawa double-exchange, which competes with the already existing antiferromagnetic superexchange, resulting in an interfacial ferromagnetic layer. Electron penetration beyond the first layer is insufficient to alter the bulk antiferromagnetism. We argue that a canted state in the first layer is possible, consistent with earlier magnetic measurements on this system. [Preview Abstract] |
Tuesday, March 6, 2007 5:18PM - 5:30PM |
L13.00013: First principles calculations of interfacial magnetism in CrO2-SnO2 rutile junctions. Mairbek Chshiev, Krishna Chetry, Arunava Gupta, William H. Butler Rutile oxides possess a wide range of interesting properties including the half metallic behavior of CrO$_{2}$ which has been shown both theoretically and experimentally to have essentially 100{\%} spin polarization. For this reason, CrO$_{2}$ has attracted interest as an electrode material for fabrication of spin-valve structures and tunnel junctions with extremely high magnetoresistance ratios. SnO$_{2}$ is considered to be an ideal candidate for such magnetic tunnel junctions since it is an insulator with the same rutile crystal structure as CrO$_{2}$. Understanding of the atomic configuration and magnetic structure at the interfaces is important for obtaining high magnetoresistance ratios because of possible mixing of Cr and Sn interfacial atoms. We report first-principles studies of the role of the magnetic structure for different interfacial intermixing configurations between Cr and Sn atoms for supercells in the (100) and (110) directions. The calculations were performed using the Vienna ab-initio simulation program (VASP) within the Generalized Gradient Approximation (GGA) to Density Functional Theory (DFT). [Preview Abstract] |
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