Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session J17: Focus Session: Magnetic Oxide Nano- & Hetero-Structures |
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Sponsoring Units: DMP GMAG Chair: Yayoi Takamura, UC Davis Room: 319 |
Tuesday, March 19, 2013 2:30PM - 2:42PM |
J17.00001: Mesoscale spin domain formation and their correlations in quasi-1D La$_{0.67}$Sr$_{0.33}$MnO$_3$ nanowires Xiaoqian M. Chen, Nick Bronn, Nadya Mason, Peter Abbamonte, Jason Hoffman, Anand Bhattacharya Creating materials with nano-scale dimensions can introduce finite size and boundary effects, where the scale of the system boundaries near criticality becomes comparable to the correlation of competing orders in the material. To study these effects, we have fabricated arrays of quasi-1D nanowires from epitaxially grown La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) thin films on SrTiO$_{3}$(STO) substrates. Our studies with resonant soft x-ray scattering (RSXS) reveal a non-trivial magnetic domain formation along different momentum directions in these wires. In addition, a new magnetic order was observed below 110K, likely induced by the STO structural transition. Below the Curie temperature we also observed a series of magnetic superlattice reflections, indicating collective mesoscale ordering of the magnetic moments into a pattern with a spatial period of five wires. Our calculations using dielectric susceptibility and Ising model simulations provide us an interpretation for the mechanism of domain formation and their long-range interaction through dipole coupling. [Preview Abstract] |
Tuesday, March 19, 2013 2:42PM - 2:54PM |
J17.00002: Dynamic resistive switching controlled by local lateral gating in phase separated manganite wires Hangwen Guo, Joo Hyon Noh, Shuai Dong, Philip Rack, Zheng Gai, Xiaoshan Xu, Elbio Dagotto, Jian Shen, Thomas Z. Ward Behaviors such as high T$_{\mathrm{c}}$ superconductivity, colossal magnetoresistivity, and the metal-insulator transition, have been tied to inherent electronic phases coexisting in a single crystal material. Here we demonstrate a novel approach to induce resistive electric field effect transitions based on the modification of the inherent electronic domain structures in single crystal materials. A phase separated manganite system confined to a scale which isolates a few electronic domains is controlled using laterally gated which give repeatable resistive changes of up to 50{\%}. This technique also makes it possible to create multistate switching devices from a single confined transport channel. These findings provide an avenue to control inherent electronic phases in strongly correlated materials as a means of creating novel nano-electronic devices. Supported by the US DOE Office of Basic Energy Sciences, Materials Sciences and Engineering Division. [Preview Abstract] |
Tuesday, March 19, 2013 2:54PM - 3:06PM |
J17.00003: Magnetic structure of epitaxial self-assembled La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ nanoislands Jone Zabaleta, Sergio Valencia, Florian Kronast, Miriam Jaafar, Patricia Abellan, Cesar Moreno, Jaume Gazquez, Oscar Iglesias-Freire, Felip Sandiumenge, Teresa Puig, Agustina Asenjo, Narcis Mestres, Xavier Obradors The mixed-valence manganite La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO), in nanoscale configuration, is a strong candidate for magnetic logic and sensor applications because of its Curie temperature (360 K) and high degree of spin polarization. In this work we unravel the magnetic structure of self-assembled ferromagnetic LSMO epitaxial nanoislands smaller than 200 nm in lateral size and less than 40 nm in height, grown using a bottom-up solution-based methodology. Magnetic force microscopy shows that LSMO islands stabilize either single domain, multidomain, or vortex state configurations, depending on their lateral size and aspect ratio. The vortex state of islands with different morphology and two distinct crystallographic orientations is further explored using spatially-resolved x-ray magnetic circular dichroism in photoemission electron microscopy measurements. The vortex evolution of individual islands is tracked in-situ by applying in-plane magnetic field. The magnetic structure study is complemented with crystal structure, strain state, and chemical composition studies. [Preview Abstract] |
Tuesday, March 19, 2013 3:06PM - 3:18PM |
J17.00004: Control with the switching behavior in exchange-coupled nanomagnets Erik Folven, Yayoi Takamura, Andreas Scholl, Andrew Doran, Anthony Young, Scott T. Retterer, Helen Gomonay, Thomas Tybell, Jostein Grepstad Control with the switching behavior of monodomain nanomagnets is key to a range of magnetic device technologies. We have recently demonstrated that shape-induced stabilization of antiferromagnetic (AFM) domains can be achieved in embedded $LaFeO_3$ thin film nanostructures.$^{1,2}$ This finding offers a pathway to influence the switching behavior of nanoscale thin film ferromagnets through exchange coupling across the interface between an antiferromagnet and a ferromagnet. Here, we show how the switching field for rectangular nanomagnets may be significantly reduced in $LaFeO_3$ (AFM)/$La_{0.7}Sr_{0.3}MnO_3$ (FM) heterostructures. Mediated by the interface exchange coupling, the engineered domains in the $LaFeO_3$ layer give rise to a uniaxial bias field acting on the magnetic moments in the $La_{0.7}Sr_{0.3}MnO_3$. By tailoring the AFM domain state, we can align this bias field perpendicular to the long axis of the magnetic element, effectively lowering the potential barrier between the two stable single domain states of the rectangular nanomagnet. The experimental data obtained with element specific x-ray spectromicroscopy is compared with a simple theoretical model. 1. Folven et al., Nano Letters 10, 4578 (2010) 2. Folven et al., Nano Letters 12, 2386 (2012) [Preview Abstract] |
Tuesday, March 19, 2013 3:18PM - 3:30PM |
J17.00005: Fabrication and study of CoF$_{2}$O$_{4}$ structures on Graphene substrates employing scanning probe microscopy techniques Irma Kuljanishvili, Marko Surtchev, John Cavin, Alexander Smetana, Saju Nattikadan Graphene materials are being investigated in recent years for verity of applications, including electric and optical devices and novel substrates. In this study we explore the route for assembling micro- and nanoscale architectures of magnetic complex oxide material directly on graphene surface using `direct write' parallel patterning techniques. Ferrimagnetic oxide CoFe$_{2}$O$_{4}$ (CFO) was prepared by sol-gel chemical route and used as `ink' for patterning structures. An array of CFO dots was fabricated using Dip Pen Nanolithography method at specific locations. Here we will discuss the surface properties of the formed dot structures of CoFe$_{2}$O$_{4}$ on graphene as compared to those formed on Si/SiO$_{2}$ substrate. Structures fabricated on each substrate with the same ambient conditions and thermal processing show different morphology and magnetic interactions when studied using AFM and MFM techniques. We will describe our findings and results acquired on individual CFO dots of different sizes. We will also show that graphene substrate is likely influencing the magnetic characteristics of CFO dots that are formed on its surface, although the role of graphene as a substrate for CFO dot formation should be further investigated. [Preview Abstract] |
Tuesday, March 19, 2013 3:30PM - 3:42PM |
J17.00006: Electrical manipulation of interface conduction in BiFeO3-CoFe2O4 columnar heterostructures Yi-Chun Chen, Ying-Hui Hsieh, Jia-Ming Liou, Chia-Ying Shen, Ying-Hao Chu Complex oxide interfaces emerge as one of the most exciting subjects in the condensed-matter field due to its unique physical properties and new possibilities for next-generation electronic devices. Recently, we found local conduction at the tubular interfaces of self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) heterostructures. In this study, to further investigate the electrical properties of the tubular oxide interface, conductive atomic force microscopy (CAFM) at different temperatures was performed to examine the sample. The origin of local conduction at the BFO-CFO vertical interface is identified as a result of the accumulation of oxygen vacancies. In addition, the interface conduction can be modulated with non-volatile and reversible behaviors via an external electric field. This memritor-like phenomenon can be understood owing to the movement of oxygen vacancies driven by the applied bias. The bias causes the oxygen vacancies either accumulate or deplete to the metal contact tip, which in turn affect the resistance at the tubular interface. Our results provide the control of the conduction at complex oxide interfaces and suggest the possibility for new devices based on complex oxide interfaces. [Preview Abstract] |
Tuesday, March 19, 2013 3:42PM - 3:54PM |
J17.00007: Self-Assembled Multiferroic Nanocomposites for Use in Magnetic Logic Architecture Ryan Comes, Mikhail Khokhlov, Hongxue Liu, Jiwei Lu, Stuart Wolf CoFe$_{\mathrm{2}}$O$_{\mathrm{4}}$ (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$_{\mathrm{3}}$ (BFO) nanostructured phase segregation occurs, with CFO pillars forming in a BFO matrix. The CFO-BFO nanocomposite system has been proposed as a possible multiferroic logic or memory scheme.[1] We will discuss the patterning and growth of CFO-BFO composites using e-beam lithography and pulsed electron deposition.[2] Our results have demonstrated the ability to pattern the composites into square arrays of pillars with spacing as small as 100 nm. The magnetic properties of the patterned films have been characterized using magnetic force microscopy and are in good agreement with previous results from our group for unpatterned composites.[3] Cross-sectional TEM analysis of the films was used to quantify the strain in the CFO pillars and evaluate the elastic anisotropy. Piezoresponse force microscopy analysis and lithographic domain patterning of the BFO matrix is also presented. [1] S.A. Wolf, et al. Proc. IEEE 98 (2010). [2] R. Comes, et al. Nano Lett. 12 (2012). [3] R. Comes, et al. J. App. Phys. 111 (2012). [Preview Abstract] |
Tuesday, March 19, 2013 3:54PM - 4:06PM |
J17.00008: Magnetoelectric effects in oxide magnetic tunnel junctions with ferroelectric barriers Javier Tornos, Y.H. Liu, S.G.E. te Velthuis, M.R. Fitzsimmons, A. Rivera, R. Lopez Anton, G. Sanchez Santolino, M. Varela del Arco, N.M. Nemes, S.J. Pennycook, Z. Sefrioui, C. Leon Yebra, J. Santamaria Functional properties of magnetic tunnel junction can be enhanced by employing a ferroelectric material as the barrier layer. We report on La0.7Sr0.3MnO3(LSMO)/BaTiO3(BTO)/LSMO magnetic tunnel junctions(MTJ) with BTO ferroelectric tunnel barrier. Switching BTO ferroelectric polarization influences the tunneling magnetoresistance (TMR) achieving two different r resistance states for each magnetic state (parallel or antiparallel) of the magnetization of the electrodes . The voltage dependence of the differential conductance obtained from IV curves displays oscillations whose period depends on the BTO electric polarization. This unusual behavior could be related to the presence of an induced magnetic moment in BTO ferroelectric barrier detected by XMCD measurements. These results reveal that spin polarization, and its tunneling conductance can be electrically tuned through reversal of the ferroelectric polarization of the barrier. [Preview Abstract] |
Tuesday, March 19, 2013 4:06PM - 4:18PM |
J17.00009: Magnetic field effects on dielectrophoresis in manganites Daniel Grant, Galin Dragiev, Amlan Biswas Perovskite-type manganese oxides (manganites) are of interest for many of the different properties they possess, including colossal magnetoresistance (CMR) and ferroelectric behavior. With the application of an electric field, large resistance decreases have been noted near the insulator-to-metal transition temperature in samples of (La$_{\mathrm{1-y}}$Pr$_{\mathrm{y}})_{\mathrm{1-x}}$Ca$_{\mathrm{x}}$MnO$_{\mathrm{3}}$ (LPCMO). Two proposed models have emerged to explain the behavior, dielectric breakdown and dielectrophoresis, with experimental evidence showing some aspects of the dielectrophoresis model to be correct. However, neither model accounts for magnetic interactions among the ferromagnetic metallic regions and the effects of a magnetic field applied in conjunction with an electric field. We have performed measurements on LPCMO samples by varying the strength and orientation of the magnetic field and the applied voltage. Cross-shaped microstructures have been made on LPCMO samples to allow us to investigate the effects of sample size on dielectrophoresis. We will present resistance and magnetization data obtained on LPCMO samples at various magnetic field strengths, magnetic field orientations, and sample sizes to elucidate the effect of magnetic interactions on dielectrophoresis induced transport and magnetic properties. [Preview Abstract] |
Tuesday, March 19, 2013 4:18PM - 4:30PM |
J17.00010: The observation and control of electronic nematic phase in manganites by stripy domains Changcheng Ju During the past decades, novel electronic liquid crystal phases have been revealed in strongly correlated electronic systems, especially the electronic nematic phase in strontium ruthenate and superconductors. Transport measurements show strongly transport anisotropies in these otherwise isotropic electronic systems. In this work, we report 71$^{\circ}$ striped ferroelectric domains created in BiFeO3 can also epitaxially lock the perovskite manganites leading to the emerge of an electronic nematic phase. Firstly, La1-xSrxMnO3/BiFeO3 (LSMO/BFO) bilayer samples are deposited by PLD. The 71$^{\circ}$ periodic striped ferroelectric domains and coherent growth are demonstrated by PFM and X-ray rocking curve. X-ray reciprocal space mapping have been used to confirm the epitaxial relationships of the layers and in-plane lattice constants. Transport measurements reveal a nematic phase transition without high magnetic fields. By changing the thickness of BFO and LSMO layer respectively, we observed substantial anisotropic resistivities and a shift of transition temperature for nematic phase and M-I transition. Unlike the other electronic liquid crystals, magnetic fields perpendicular to the film can suppress the appearance of nematic phase. XMCD and NEXAFS at the Mn L2, 3 edge revealed an in-plane preferential occupation of orbitals and a broken rotational symmetry for Mn-O-Mn bonds at nematic phase. At last, we also demonstrate a nonvolatile electric-field control of anisotropic resistivity switching. [Preview Abstract] |
Tuesday, March 19, 2013 4:30PM - 4:42PM |
J17.00011: Characterization of interfacial charge accumulation in ferroelectric BaTiO$_3$/manganite interfaces using atomic-resolution annular bright field imaging and electron energy-loss spectroscopy Robert Klie, Qiao Qiao, Patrick Phillips, Hanghui Chen, Matthew Marshall, Fred Walker, Sohrab Ismail-Beigi, Charles Ahn Interfaces in functional oxides have been the focus of many studies due to potential emergence of novel phases. In this study, we will focus on ferroelectric/manganite, more specifically the LaSrMnO$_3$/BaTiO$_3$ interfaces in single-crystal thin films grown on SrTiO$_3$. Using atomic-resolution annular bright field (ABF) imaging, as well as atomic-column resolved electron energy-loss spectroscopy in the aberration-corrected, cold-field emission gun JEOL ARM200CF, we will demonstrate that the interfacial accumulation/depletion of charges, depending on the orientation of the ferroelectric polarization, can be directly quantified. We find that the interfacial accumulation of electron/holes is screen within three unit-cells of LaSrMnO$_3$. Moreover, using ABF imaging, we will shows that the distortions of the oxygen sublattice can be directly quantify, in both the BaTiO$_3$ layer, as well as the interfacial LaSrMnO$_3$. Our experimental results imaging and spectroscopy results will be complemented by first-principles density functional theory calculations. [Preview Abstract] |
Tuesday, March 19, 2013 4:42PM - 4:54PM |
J17.00012: Magnetic properties of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/BaTiO$_{3}$ interfaces Yaohua Liu, S.G.E. te Velthuis, J.W. Freeland, N.J. Tornos, C. Leon, J. Santamaria Interfaces between the ferromagnetic (FM) and ferroelectric (FE) oxides may host nanoscale multiferroic phases with strong magnetoelectric coupling, which can be potentially utilized for energy-efficient spintronics. In this work, we have investigated the magnetic properties of the interface between ferromagnetic La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) and ferroelectric BaTiO$_{3}$ (BTO) via X-ray resonant magnetic scattering (XRMS) and X-ray magnetic circular dichroism (XMCD) on a series of 10 nm LSMO / t BTO bilayers, with t = 1.2, 2.4 and 4.8 nm, respectively. Additionally, we have studied a LSMO/BTO/LSMO trilayer. Interestingly, we have observed magnetic dichroism from Ti ions between 30 K and 210 K, which closely tracks the Mn's dichroism during the magnetization reversal. In contrast, no Ti magnetization has been observed in a single-layer BTO film on a SrTiO$_{3}$ substrate. These results suggest that there are Ti$^{3+}$ ions that reside at the LSMO/BTO interfaces and the interfacial Mn and Ti moments are exchange coupled. [Preview Abstract] |
Tuesday, March 19, 2013 4:54PM - 5:06PM |
J17.00013: Magnetoelectric coupling at the EuO/BaTiO$_{3}$ interface Shi Cao, Pan Liu, Jinke Tang, Chung Wung Bark, Sangwoo Ryu, Chang Beom Eom, Peter Dowben, Alexei Gruverman Magnetization modulation by ferroelectric polarization pinning is reported for the ferromagnetic-ferroelectric EuO/BaTiO$_{3}$ (EuO/BTO) heterostructures. Away from T$_{c}$, the critical exponent $\beta $ indicates that the magnetization of EuO is consistent with mean field theory despite suggestions that EuO is a typical Heisenberg ferromagnetic semiconductor. The Heisenberg model is also inconsistent with the significant band dispersion seen in EuO thin films. The possible mechanisms include extrinsic doping and/or pinning of interface states at the EuO/BTO interface. The results are discussed in the context of data also obtained for La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/BaTiO$_{3}$ heterostructures, where the critical exponent $\beta $ is also close to the predictions of mean field theory, suggesting a similarity in the importance of the magnetic interface with a ferroelectric and the possible importance of ferroelectric polarization reversal. [Preview Abstract] |
Tuesday, March 19, 2013 5:06PM - 5:18PM |
J17.00014: Coupled ferromagnetism and ferroelectricity in superlattices of non-ferroelectric antiferromagnetic manganites J.D. Burton, K. Rogdakis, J.W. Seo, Z. Viskadourakis, Y. Wang, L. Ah Qune, E. Choi, E. Tsymbal, J. Lee, C. Panagopoulos Complex oxide heterostructures present a promising avenue for the design of multifunctional properties which may find application in a variety of technological systems. In heterostructures composed of transition metal oxides the disruption introduced by an interface can affect the balance of the competing interactions among spins, charges and orbitals. This has led to the emergence of properties absent in the original building blocks of a heterostructure. We will report on the discovery of magnetically tunable ferroelectricity in artificial tri-layer superlattices consisting of non-ferroelectric and non-ferromagnetic components: NdMnO$_3$/SrMnO$_3$/LaMnO$_3$.[1] Ferroelectricity was observed below 40 K exhibiting strong tunability by superlattice periodicity. Furthermore, magnetoelectric coupling resulted in 150{\%} magnetic modulation of the polarization. First-principles calculations indicate that broken space inversion symmetry and mixed valency give rise to the observed behavior. This discovery highlights the importance of tri-layered systems for the engineering of emergent properties in oxide heterostructures. [1] K. Rogdakis et al, Nat Commun 3, 1064 (2012) [Preview Abstract] |
Tuesday, March 19, 2013 5:18PM - 5:30PM |
J17.00015: Anomalous exchange bias at collinear/noncollinear spin interface Tao Wu We report on the interfacial magnetic coupling in manganite bilayers of collinear ferromagnetic La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ and noncollinear multiferroic TbMnO$_{3}$. Exchange bias emerges at the Neel temperature of TbMnO$_{3}$ (about 41 K) due to the onset of long-range antiferromagnetic ordering in the Mn spin sublattice. Interestingly, an anomalous plateau of exchange bias emerges at the ordering temperature of Tb spins (about 10 K), and we ascribe this unique feature to the strong coupling between Tb and Mn spin sublattices in TbMnO$_{3}$, which in turn influence the magnetic coupling across the interface. On the other hand, the enhancement of coercivity in La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ shows monotonous temperature dependence. Our results illustrate a strong interfacial magnetic coupling at the La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/TbMnO$_{3}$ interface, highlighting the roles of competing spin orders, magnetic frustration, and coupling between multiple spin sublattices in artificial collinear/noncollinear spin heterostructures. [Preview Abstract] |
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