Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session J32: Focus Session: Manganite Heterostructures and Interfaces |
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Sponsoring Units: GMAG DMP Chair: T. Zac Ward, Oak Ridge National Laboratory Room: 207B |
Tuesday, March 3, 2015 2:30PM - 3:06PM |
J32.00001: Oscillatory Non-collinear Magnetism Induced by Interfacial Charge Transfer in Metallic Oxide Superlattices Invited Speaker: Jason Hoffman Non-collinear magnetic textures give rise to interesting charge and spin transport properties, and allow for control of magnetism using small electric currents. While these textures have been observed in a number of bulk materials and in thin films, realizing non-collinear magnetism in heterostructures presents new avenues to control their properties using tailored interfaces and gate electric fields. We have discovered a non-collinear magnetic coupling in superlattices comprised of two metallic perovskites, La$_{2/3}$Sr$_{1/3}$MnO$_3$ (LSMO) and LaNiO$_3$ (LNO). The superlattices are synthesized using oxide molecular beam epitaxy, and characterized with a variety of means, including x-ray and neutron scattering. We find that the angle between the magnetization of the LSMO layers varies in an oscillatory manner with the thickness of the intervening LNO. The magnetic field and temperature dependence of this coupling angle cannot be explained using models that incorporate bilinear and biquadratic coupling, which are commonly used to describe non-collinear magnetism in conventional metallic heterostructures. Furthermore, we observe substantial electron transfer from the LSMO into the LNO layer, causing the Ni sites in the vicinity of interfaces to be in approximately a 2+ oxidation state. We propose a model where these localized Ni$^{2+}$ spins in the LNO couple to a momentum dependent spin susceptibility, giving rise to a spiral magnetic structure within the LNO. [Preview Abstract] |
Tuesday, March 3, 2015 3:06PM - 3:18PM |
J32.00002: Influence of structural asymmetries on LaNiO$_{3}$-LaMnO$_{3}$ interfaces Marta Gibert, Michel Viret, Pavlo Zubko, Sara Catalano, Cinthia Piamonteze, Nicolas Jaouen, Jean-Marc Tonnerre, Almudena Torres-Pardo, Alex Gloter, Odile Stephan, Jean-Marc Triscone Complex electronic reconstruction at interfaces between transition metal oxides play a key role on the emergence of novel functionalities in these materials. In this context, we reported on the observation of exchange bias in superlattices composed of nominally paramagnetic metallic LaNiO$_{3}$ and semiconducting ferromagnetic LaMnO$_{3}$ ultrathin layers [1], which exemplifies how interface engineering can induce a magnetic structure in LaNiO$_{3}$. Here, we investigate the properties of LaNiO$_{3}$-LaMnO$_{3}$ bilayers, i.e. SrTiO$_{3}$//8u.c.LaNiO$_{3}$/8u.c.LaMnO$_{3}$. TEM images have shown that the interface LaNiO$_{3}$/LaMnO$_{3}$ is sharper than the LaMnO$_{3}$/LaNiO$_{3}$ one, which displays two monolayers intermixing. This structural asymmetry results into very distinct properties: enhanced conductivity and extremely reduced magnetization is observed for the ``sharp interface'' samples in contrast to the rough ones. State-of-the-art synchrotron techniques reveal differences in interfacial charge transfer and induced magnetic moments in the Ni atoms, and allow us to reproduce the magnetic profile of each LMO layer. The role of orbital occupation will also be explored.\\[4pt] [1] Gibert et al., Nat. Mater .11, 195 (2012). [Preview Abstract] |
Tuesday, March 3, 2015 3:18PM - 3:30PM |
J32.00003: ABSTRACT WITHDRAWN |
Tuesday, March 3, 2015 3:30PM - 3:42PM |
J32.00004: Charge and Strain Control of Interface Magnetism M.R. Fitzsimmons, K. Dumesnil, N. Jaouen, T. Maroutian, G. Agnus, J.-M. Tonnerre, B. Kirby, E. Fohtung, B. Holladay, E.E. Fullerton, O. Shpyrko, S.K. Sinha, Q. Wang, A. Chen, Q.X. Jia We studied the influence of an electric field applied to an La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) layer in a LSMO/Pb(Zr$_{0.2}$Ti$_{0.8})$O$_{3}$ (PZT)/Nb-doped SrTiO$_{3}$ (STO) heterostructure by measuring its magnetization depth profile using resonant x-ray magnetic reflectivity. The saturation magnetization of the ferromagnetically-ordered LSMO was not affected by the direction of the polarization of the PZT. However, the ferromagnetic thickness and magnetization of the LSMO film at remanence were reduced for hole-charge accumulation at the LSMO/PZT interface. To understand the \textit{independent} roles of strain and hole-doping, we performed neutron scattering experiments of La$_{0.8}$Sr$_{0.2}$MnO$_{3}$ films grown on Nb-doped STO in which bending strain (via 4-point bending jig) \textit{or} electric field (via parallel plate capacitor) was applied to the films. We observed that bending strain affects the saturation magnetization of the LSMO film, whereas electric field affects the remanent magnetization of the film. These observations suggest strain may be a more effective means to control magnetism than charge. [Preview Abstract] |
Tuesday, March 3, 2015 3:42PM - 3:54PM |
J32.00005: Mapping magnetism with atomic resolution using aberrated electron probes Juan Idrobo, J\'an Rusz, Michael A. McGuire, Christopher T. Symons, Ranga Raju Vatsavai, Andrew R. Lupini In this talk, we report a direct experimental real-space mapping of magnetic circular dichroism with atomic resolution in aberration-corrected scanning transmission electron microscopy (STEM). Using an aberrated electron probe with customized phase distribution, we reveal with electron energy-loss (EEL) spectroscopy the checkerboard antiferromagnetic ordering of Mn moments in LaMnAsO by observing a dichroic signal in the Mn L-edge. The aberrated probes allow the collection of EEL spectra using the transmitted beam, which results in a magnetic circular dichroic signal with intrinsically larger signal-to-noise ratios than those obtained via nanodiffraction techniques (where most of the transmitted electrons are discarded). The novel experimental setup presented here, which can easily be implemented in aberration-corrected STEM, opens new paths for probing dichroic signals in materials with unprecedented spatial resolution. [Preview Abstract] |
Tuesday, March 3, 2015 3:54PM - 4:06PM |
J32.00006: Insight into spin transport in oxide heterostructures from interface-resolved magnetic mapping M.N. Grisolia, F.Y. Bruno, C. Visani, S. Valencia, R. Abrudan, A.A. Unal, M. Varela, J. Tornos, A. Rivera-Calzada, Z. Sefrioui, C. Leon, J. Santamaria, S. J. Pennycook, J.E. Villegas, A. Barthelemy, M. Bibes At interfaces between complex oxides electronic, orbital and magnetic reconstructions may produce states of matter absent from the materials involved, offering novel possibilities for electronic and spintronic devices. Here we show that magnetic reconstruction has a strong influence on spin transport. In epitaxial heterostructures combining layers of antiferromagnetic LaFeO$_{3}$ (LFO) and ferromagnetic La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO), we find that a net magnetic moment is induced in the first few unit planes of LFO near the interface with LSMO. Using Xray photoemission electron microscopy, we show that the ferromagnetic domain structure of the manganite electrodes is imprinted into the antiferromagnetic tunnel barrier, endowing it with spin selectivity. Finally, we find that coexisting ferromagnetic and antiferromagnetic interactions strongly influence the tunnel magnetoresistance of LSMO/LFO/LSMO junctions through competing spin polarization and spin filtering effects. [Preview Abstract] |
Tuesday, March 3, 2015 4:06PM - 4:18PM |
J32.00007: Exchange coupling in (111)-oriented La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/La$_{0.7}$Sr$_{0.3}$FeO$_{3}$ superlattices Yue Jia, Rajesh Chopdekar, Elke Arenholz, Anthony Young, Matthew Marcus, Andreas Scholl, Yayoi Takamura Epitaxial La$_{0.7}$Sr$_{0.3}$MnO$_{3}$(LSMO)/La$_{0.7}$Sr$_{0.3}$FeO$_{3}$(LSFO) superlattices serve as ideal systems to explore the magnetic structure and exchange coupling in (111)-oriented perovskite oxides. The (111) orientation offers a buckled honeycomb structure resembling that of graphene with the stacking of highly polar layers. Furthermore, the bulk LSFO magnetic structure predicts that the (111) interface should have fully uncompensated antiferromagnetic (AF) moments leading to exchange bias interactions. Detailed soft x-ray magnetic spectroscopy and microscopy reveal that interfacial effects and the ultrathin nature of the sublayers of the superlattices can stabilize orientations of the LSFO AF spin axis which differ from that of LSFO films and LSMO/LSFO bilayers. A portion of the interfacial AF moments can be reoriented to an arbitrary direction by a moderate external magnetic field through spin-flop coupling with the ferromagnetic LSMO sublayers with low magnetocrystalline anisotropy in the (111) plane. The remaining decoupled moments are pinned by the crystalline anisotropy, displaying 3-fold symmetry consistent with the crystal symmetry of the (111) plane. [Preview Abstract] |
Tuesday, March 3, 2015 4:18PM - 4:30PM |
J32.00008: ABSTRACT WITHDRAWN |
Tuesday, March 3, 2015 4:30PM - 4:42PM |
J32.00009: ABSTRACT WITHDRAWN |
Tuesday, March 3, 2015 4:42PM - 4:54PM |
J32.00010: Signatures of a Two-Dimensional Ferromagnetic Electron Gas at the La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/ SrTiO$_{3}$ Interface Arising From Orbital Reconstruction Maria J. Calderon, Norbert Nemes, Juan Ignacio Beltran, Flavio Bruno, Javier Garcia-Barriocanal, Zouhair Sefrioui, Carlos Leon, Mar Garcia-Hernandez, Carmen Mu\~noz, Luis Brey, Jacobo Santamaria The interface between two different oxides has properties different from the ones corresponding to the constituent layers in bulk. Different orders can arise due to the complexity of these materials in which the orbital degree of freedom, magnetism and lattice are strongly interdependent. Here we present a joint theoretical-experimental effort to understand the properties of a multilayer formed by a metallic ferromagnetic manganite oxide (La$_{0.7}$Sr$_{0.3}$MnO$_{3})$ and the insulating SrTiO$_{3}$. Magnetoresistance measurements as a function of the relative angle between the magnetic field and the interface plane have shown an unexpected in-plane peak. Calculations of resistivity in a model system including spin-orbit coupling reveal that the unexpected in-plane maximum is due to transport through a two-dimensional ferromagnetic electron gas formed by orbital reconstruction at the manganite interface. These orbital and magnetic reconstructions are supported by X-ray linear dichroism and ab-initio calculations. Advanced Materials DOI:10.1002/adma.201402829. [Preview Abstract] |
Tuesday, March 3, 2015 4:54PM - 5:06PM |
J32.00011: Emergent ferromagnetism in NdMnO3/SrMnO3 superlattices Artur Glavic, Stuart Calder, Valentino Cooper, Hemant Dixit The phenomenon of ferromagnetism evolving in digital superlattices of two antiferromagnets LaMnO3[2n]/SrMnO3[n] has been well established [1-2]. We show that this interface effect can be observed in systems with different rare earth manganites as well, exemplified in the Nd system grown on LSAT and TbScO3 substrates. With polarized neutron reflectometry we prove that not only 2/1 unit cell samples become ferromagnetic but that interface ferromagnetism can be induced whenever a single layer of SrMnO3 is introduced in the NdMnO3 system. These results show that the strain state of the superlattice system is of much less importance for the induced magnetization then the Mn3+/Mn4+ electronic state. \\[4pt] [1] P. Salvador, et al., \textbf{Appl. Phys. Lett.} 75, 2638 (1999).\\[0pt] [2] S. Dong, et al., \textbf{Phys. Rev. B} 86, 205121 (2012). [Preview Abstract] |
Tuesday, March 3, 2015 5:06PM - 5:18PM |
J32.00012: Observation of a Three-Dimensional Quasi-Long-Range Charge Order in YBa$_{2}$Cu$_{3}$O$_{7-x}$/La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ Heterostructures Thomas Mion, Junfeng He, Padraic Shafer, Vu Thanh Tra, Qing He, Jiunn-Yuan Lin, Ying-Hao Chu, Elke Arenholz, Ruihua He Heterostructures with strong interfacial effects can exhibit novel physical properties non-existent in either of the constituent materials alone. In particular, striking phenomena are observed when materials with mutually incompatible order parameters are put together by interface control on the atomic level. YBa$_{2}$Cu$_{3}$O$_{7-x}$/La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ (YBCO/LCMO) heterostructures, the combinations of a high temperature superconductor and a ferromagnet, have attracted much recent attention due to the strong modifications to the original properties of the constituent materials, including an orbital reconstruction at the interface and an unexpected persistence of the proximity effect between superconductivity and ferromagnetism significantly away from the interface. Here, we report a new electronic order in this system which competes with superconductivity. It is a three-dimensional quasi-long-range charge order, distinct from the recently observed two-dimensional charge order in bulk YBCO. Our finding contributes to establishing YBCO/LCMO) heterostructures as a unique material platform in which superconductivity, charge order and ferromagnetism coexist and interact with each other. [Preview Abstract] |
Tuesday, March 3, 2015 5:18PM - 5:30PM |
J32.00013: The Electrophoretic-like Mechanism of Huge Current effect in Electronically Phase Separated Manganite Wires Lifeng Yin, Wengang Wei, Jian Shen Electronically phase separated (La, Pr)CaMnO$_{\mathrm{3}}$ manganite wires are found to exhibit huge current effect. As the current density increase, the resistivity of wires decrease dramatically, and the metal-insulator transition temperatures get enhanced. However, the Superconducting Quantum Interference Device measurements show that the magnetizations with current on and off are almost identical. It is further confirmed by magnetic force microscope measurements, i.e. the current only changes the shape of ferromagnetic domain, while not the volume of ferromagnetic domain. The results conform to a phenomenological model in which the inherent nanoscale insulating and metallic domains are rearranged through electrophoretic-like processes to open and close percolation channels. [Preview Abstract] |
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