Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session L32: Focus Session: Nanostructured Manganites, Thin Films and Others |
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Sponsoring Units: GMAG DMP Chair: Hariharan Srikanth, University of South Florida Room: 336 |
Tuesday, March 17, 2009 2:30PM - 2:42PM |
L32.00001: Growth and characterization of the La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ nanowires Jugdersuren Battogtokh, Sungmu Kang, Robert S. DiPietro, Donald Heiman, Andrew C. Buechele, Ian L. Pegg, John Philip Conventional electrospinning method provides a simple approach to synthesis polymer nanowires. In this work, we report the growth, structural characterization, and magnetic properties of half-metallic, ferromagnetic La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) alloy nanowires that are first time grown on Si/SiO$_{2 }$substrates by the electrospinning method. Electrospun nanowires are annealed in an ultra-high purity argon-hydrogen gas mixture. Uniform, continuous, high aspect ratio LSMO nanowires with diameters in the range of 60--300 nm and lengths up to 500 $\mu $m are grown. The temperature dependent magnetization behavior of LSMO nanowires shows ferromagnetic behavior, and symmetric hysteresis loops are observed with magnetic fields applied to the substrate at 10 K and 300 K. Finally, we will discuss the spin dependent electrical transport properties of the single LSMO nanowire. [Preview Abstract] |
Tuesday, March 17, 2009 2:42PM - 2:54PM |
L32.00002: Resonant soft x-ray scattering from La$_{\mbox{1-x}}$Sr$_{\mbox{x}}$MnO$_{\mbox{3}}$ quantum wire arrays Shuai Wang, Serban Smadici, James Lee, Michael Odlyzko, Xiaofang Zhai, James Eckstein, Amish Shah, Jian-Min Zuo, Peter Abbamonte, Anand Bhattacharya Any finite sized, patterned system with an energy gap is expected to have elementary excitations that are characteristic of its boundary. To test this idea we have fabricated large arrays ($>60000$ elements) of colossal magnetoresistance- phase $\mbox{La}_{\mbox{2/3}} \mbox{Sr}_{\mbox{1/3}} \mbox{MnO}_{\mbox{3}}$ quantum wires. These wires are 80 nm in width so have properties that are dominated by edge effects. We used resonant soft x-ray scattering (RSXS) and SQUID magnetometry to study their magnetic properties. We found that patterning lowers the Curie temperature and suppresses the degree of magnetization. RSXS studies show diffraction maxima from the wire period, as well as temperature-dependent diffuse scattering. We will discuss these results in the context of combined structural and magnetic disorder. Funding \#: DOE grants DE-FG02-07ER46453 and DE-FG02-06ER46285 [Preview Abstract] |
Tuesday, March 17, 2009 2:54PM - 3:06PM |
L32.00003: Structure driven collapse of charge ordering in La$_{0.5}$Ca$_{0.5}$MnO$_{3}$ nanoparticles A.K. Raychaudhuri, Tapati Sarkar, E. Bozin, T. Proffen, T. Chatterji, S. Billinge High resolution X-Ray and neutron diffraction had been used to show that size reduction below a certain size ( $<$ 150nm) can lead to a collapse of the charge and orbitally ordered as well as the Antiferromagnetic ground state of the half doped manganite La$_{0.5}$Ca$_{0.5}$MnO$_{3 .}$This leads to a ferromagnetic ground state. We show that the phenomena is linked to the structural changes that accompany the size reduction. The low temperature (T$\sim $15K) structure of the nanocrystals is significantly different from that of the bulk. The structure of the nanoparticles shows a distortion albeit different from that seen in the bulk which is driven by the Jahn -- Teller distortion. The Rietveld analysis along with analysis of the Pair Distribution Function data show that there are differences in the way the MnO$_{6}$ octahedra are distorted in the bulk and the nanocrystals. We find that in the nanocrystals the structural distortion sets in at room temperature and shows very little variation on cooling. The Bragg peak of the ferromagnetic order in the nanoparticles was found to have the same indexes and approximately same d -- spacing as that seen in ferromagnetic La$_{0.67}$Ca$_{0.33}$MnO$_{3}$. [Preview Abstract] |
Tuesday, March 17, 2009 3:06PM - 3:18PM |
L32.00004: Jahn-Teller contribution to the magneto-optical response of ferromagnetic manganite thin films Gervasi Herranz, David Hrabovsky, Jose Manuel Caicedo, Ingrid Canero-Infante, Florencio Sanchez, Josep Fontcuberta We report on the temperature dependence of the magneto-optical response in the visible spectrum of ferromagnetic manganite thin films measured in transverse Kerr geometry. We show that this response is dominated by the usual magneto-optical Kerr effects for all temperatures except for a narrow window around the Curie temperature (T$_{C})$. Remarkably, the magneto-optical response of these manganite films does not die out near the ferromagnetic transition, in spite of the vanishing Kerr effect at those temperatures. On the contrary, the transverse Kerr response is hugely enhanced near T$_{C}$ and follows the same temperature dependence as the colossal magnetoresistance. We attribute these remarkable phenomena to the magnetic field-induced suppression of Jahn-Teller dynamical charge localization around T$_{C}$. Thus, the peculiar optical response of manganite films comes from the intricate physics of these strongly correlated electronic systems. We argue that the methodology we use is demonstrated to be very useful to understand the nature of some structural and electronic transitions driven by magnetic/electric fields or by temperature in other complex oxides. [Preview Abstract] |
Tuesday, March 17, 2009 3:18PM - 3:30PM |
L32.00005: Observation of Ferromagnetic Resonance in SrRuO$_{3 }$Using the Time-Resolved Magneto-Optical Kerr Effect M.C. Langner, C.L.S. Kantner, Y.H. Chu, L.W. Martin, R. Ramesh, J. Orenstein We report the observation of ferromagnetic resonance (FMR) in strontium ruthenate using the time-resolved magneto-optical Kerr effect. The FMR oscillations in the time-domain appear in response to a sudden, optically induced change in the direction of easy-axis anistropy. The large FMR frequency, 250 GHz, and damping parameter are consistent with strong spin-orbit coupling. The damping coefficient, as well as other parameters associated with the magnetization dynamics, have a non-monotonic temperature dependence, suggestive of a link to the anomalous Hall effect. [Preview Abstract] |
Tuesday, March 17, 2009 3:30PM - 3:42PM |
L32.00006: ABSTRACT WITHDRAWN |
Tuesday, March 17, 2009 3:42PM - 3:54PM |
L32.00007: ABSTRACT WITHDRAWN |
Tuesday, March 17, 2009 3:54PM - 4:06PM |
L32.00008: Swiching Spectroscopy Piezoresponse Force Microscopy study of Domain Wall hysteresis at the nanoscale: Mapping lattice and defect pinning effects Vasudeva Rao Aravind, Samrat Choudhury, Yulan Li, Katyayini Seal, Stephen Jesse, Anna Morozovska, Eugene Eliseev, Long-Qing Chen, Sergei Kalinin, Venkatraman Gopalan In this work,~Using scanning probe microscopy with $\sim $10 nanometer resolution along with theoretical modeling, we demonstrate the role of 180$^{o}$ ferroelectric domain wall as an intrinsic defect that lowers coercive fields in its vicinity by an order of magnitude. The interaction of ferroelectric 180$^{o}$ domain wall with a strongly inhomogeneous electric field of biased scanning probe microscope tip is analyzed within decoupling approximation allowing for the spatial redistribution of polarization caused by the biased probe using continuous Landau-Ginzburg-Devonshire theory. Theoretical calculations predict that equilibrium shape of the initially flat domain wall boundary bends, attracts or repels from the probe apex. The bending of the wall and its depolarization electric field facilitates tip induced domain nucleation. The experiments and theory are compared quantitatively, to show that lattice friction as well as lattice pinning play important role in the domain wall softening behavior. \underline {Acknowledgements:} [1] National Science Foundation, [2] Center for Nanophase Materials Sciences, Oak Ridge National Laboratory. [Preview Abstract] |
Tuesday, March 17, 2009 4:06PM - 4:18PM |
L32.00009: Controlling Orthorhombic Domain Orientations in Epitaxial LaPrCaMnO Thin Films John Budai, T. Zac Ward, Jon Tischler, Jian Shen Microstructural effects such as strain and domain formation are known to influence the physical properties of transition metal oxide materials. For epitaxial films, lattice mismatch with the substrate can be used to investigate the effects due to in-plane biaxial tensile or compressive strain. Using synchrotron x-ray diffraction at the Advanced Photon Source, we have investigated the temperature-dependent lattice parameters and orthorhombic domain orientations for distorted perovskite LaPrCaMnO thin films grown on several different substrates (SrTiO3, LaAlO3, SrLaGaO4, NdGaO3). We find that structural phase transition in the substrate can have a large effect on the film. More generally, we find that tensile and compressive stresses generate different orthorhombic domain orientations and can be used to control the microstructure of the LPCMO films . [Preview Abstract] |
Tuesday, March 17, 2009 4:18PM - 4:30PM |
L32.00010: Effect of the substrate on the orbital phase transition in a manganite thin film under magnetic field Y. Wakabayashi, H. Sagayama, T. Arima, Y. Nakamura, Y. Ogimoto, K. Miyano, H. Sawa Thin films of strongly correlated materials are studied intensively because of their potential of device application. Those materials in bulk form show various fascinating properties such as metal-insulator transition. However, clear phase transitions are often suppressed under the strain from the substrates. We have studied Nd$_{0.5}$Sr$_{0.5}$MnO$_3$ thin film on SrTiO$_3$ (011) substrate, which is a unique film that has clear orbital-ordering (OO) transition, by x-ray scattering under magnetic field up to 8T. As reported earlier [1], this system show three phase transitions, paramagnetic (PM), ferromagnetic (F), A-type OO (A) to CE-type OO (CE) with cooling in zero field, and at F-A transition temperature (170K), the symmetry lowers and twin occurs. The phase sequence was changed to PM, F to CE above 4T, and above this field, considerable amount of the FM phase remains down to 10K. This field induced phase separation is attributable to the martensitic accommodation strain at the domain boundary. [1]Y.W. et al., Phys. Rev. Lett. {\bf 96} 017202 (2006), J.Phys.Soc.Jpn. {\bf 77}, 014712 (2008). [Preview Abstract] |
Tuesday, March 17, 2009 4:30PM - 4:42PM |
L32.00011: Coherent Long Range Lateral Charge Ordering in strained Epitaxial Oxide Film Structures. Jong-Woo Kim, Philip Ryan, Jak Chakhalian, Mikhail Kareev, Jian Liu, Steve May, Anand Bhattacharya, John Freeland The quality of ordered oxide films has reached the level whereby epitaxial superlattice structures can now be achieved by both pulsed laser deposition (PLD) and ozone assisted molecular beam epitaxial (MBE) growth. Engineering each layer coupled with compressive and tensile strain with the explicit aim of controlling and or enhancing the macroscopic electrical and magnetic ordering is a considered aim of ordered oxide film growth. The question how highly strained films structurally respond to such stress is examined by synchrotron diffraction. Both LaSrMnO films grown on STO(001) by MBE and PLD grown LaNiAlO films on both LAO(001) and STO(001) have revealed coherent lateral ordering dependent upon film disorder, substrate mismatch induced strain and even dislocations induced by the substrate step morphology. [Preview Abstract] |
Tuesday, March 17, 2009 4:42PM - 4:54PM |
L32.00012: Dember effect induced photovoltage in perovskite \textit{p}-\textit{n} heterojunctions Kui-juan Jin, Kun Zhao, Hui-bin Lu, Leng Liao, Guo-zhen Yang An unusual and rather large transient lateral photovoltage (LPV) has been observed in La$_{0.9}$Sr$_{0.1}$MnO$_{3}$/SrNb$_{0.01}$Ti$_{0.99}$O$_{3}$ and La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/Si heterojunctions under the nonuniform irradiation of pulsed laser. The irreversible LPVs on both sides of a $p-n $ junction challenge the well established model for LPV in conventional semiconductor $p-n$ junctions, which can be well explained by Dember effect. Much larger LPV is observed in La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/Si than that in La$_{0.9}$Sr$_{0.1}$MnO$_{3}$/SrNb$_{0.01}$Ti$_{0.99}$O$_{3}$. Similar results measured from both substrates of SrNb$_{0.01}$Ti$_{0.99}$O$_{3}$ and Si also support such a Dember effect. Much larger LPVs in heterojunctions than those in simple samples (SrNb$_{0.01}$Ti$_{0.99}$O$_{3}$ or Si) suggest a potential application of Dember effect in heterostructures. [Preview Abstract] |
Tuesday, March 17, 2009 4:54PM - 5:06PM |
L32.00013: Ellipsometric Study of the Electronic Band Structure of CrO$_2$ across the Ferromagnetic Transition M.K. Stewart, B. Chapler, M.M. Qazilbash, A.A. Schafgans, D.N. Basov, K. Chetry, A. Gupta, T. Tiwald We present a detailed study of the optical properties of half metallic CrO$_2$ at temperatures below, at, and above the Curie temperature. The films were grown epitaxially on (100) and (110) oriented TiO$_2$ substrates by chemical vapor deposition. Using variable angle spectroscopic ellipsometry we have extracted the optical conductivity of the films in the range from 0.06 to 6 eV. Our data reveal an important anisotropy in the films which is in good agreement with what is know about their crystal structure. The main features of the conductivity spectra in the ferromagnetic state are consistent with existing band structure calculations. However, we observe no temperature dependence of these features across the ferromagnetic transition, posing questions about the electronic structure of the material. [Preview Abstract] |
Tuesday, March 17, 2009 5:06PM - 5:18PM |
L32.00014: Spins and Twins: Correlation between Crystallographic and Magnetic Domains at Co/NiO(001) Interfaces Hendrik Ohldag, Elke Arenholz, Gerrit van der Laan Using soft x-ray spectromicroscopy we show that NiO(001) exhibits a crystallographic and magnetic domain structure near the surface identical to that of the bulk. Upon Co deposition a perpendicular coupling between the Ni and Co moments is observed that persists even after formation of uncompensated Ni spins at the interface through annealing. The chemical composition at the interface alters its crystallographic structure and leads to a reorientation of the Ni moments from the h112i to the h110i direction. We show that this reorientation is driven by changes in the magnetocrystalline anisotropy rather than exchange coupling mediated by residual uncompensated spins. [Preview Abstract] |
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