Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session T17: Focus Session: Magnetic Oxide Thin Films - Manganite Thin Films |
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Sponsoring Units: GMAG DMP Chair: John Freeland, Argonne National Laboratory Room: D174 |
Wednesday, March 23, 2011 2:30PM - 3:06PM |
T17.00001: Tunable Percolative Transport in Manganite Thin Films using Strain and Exchange Fields Invited Speaker: Strongly correlated electronic systems are often sensitively dependent on spin-charge-orbital-lattice interactions. We will discuss recent work on manganites that have led to some fascinating new discoveries on the role of these interactions in driving electronic phase separation in strongly correlated systems. We demonstrate that substrate induced anisotropic strain effects and surface exchange coupled magnetic nanodots can be used to preferentially seed electronic domains. These effects have led to a new understanding of how order parameter tuning can lead to highly controllable electronic and magnetic properties. We find that even strain frustrated ultrathin manganite films---where no metal-insulator transition is present---can be selectively tuned with the application of magnetic nanodots at the film surface. Both the magnetoresistance and the metal-insulator transition temperature can be tuned through dot density and dimension. The strain frustrated film's metal-insulator transition and magnetoresistivity can be driven to bulk levels. We expect these results to be applicable in many other systems in which order parameters are tightly correlated. [Preview Abstract] |
Wednesday, March 23, 2011 3:06PM - 3:18PM |
T17.00002: STM study on the electronic phase separation of manganites Min Gao, Zheng Gai, Paul C. Snijders, Hangwen Guo, Thomas Z. Ward, H.-J. Gao, Jian Shen Phase separation is a key problem in understanding the exotic properties of complex oxide materials. Combing pulsed laser deposition with in situ scanning tunneling microscopy, we can investigate the electronic phase separation ofLa$_{5/8-x}$Pr$_{x}$Ca$_{3/8}$M nO$_{3}$. Current imaging tunneling spectroscopy reveals both local domain contrast and global conductivity evolving when the temperature crosses over the metal-insulator transition temperature. The domain size can be several hundred nanometers. This result confirms other experimental results and shows that the surface electronic properties of complex oxide materials can represent their bulk properties. [Preview Abstract] |
Wednesday, March 23, 2011 3:18PM - 3:30PM |
T17.00003: Nonlinear optical imaging of antiferromagnetic domains in orbital-ordered Pr$_{0.5}$Sr$_{0.5}$MnO$_{3}$ thin films Kenjiro Miyano, Naoki Ogawa, Yasushi Ogimoto Perovskite manganites develop various ordering patterns of charge, orbital, and spin, whose geometrical correlation brings out a new order, e.g., electronic polarization. As an example in pseudo-cubic systems, the CE-type charge/orbital order (CO/OO) was predicted to be multiferroic. With the use of nonlinear optics, we show that Pr$_{0.5}$Sr$_{0.5}$MnO$_{3}$ thin films exhibit symmetry breaking in the OO phase without CO. Ultrathin films prepared on LSAT(110) substrates reproduce bulk-like properties, showing successive phase transitions from paramagnetic metal, to ferromagnetic metal, and finally to A-type antiferromagnetic (AF) insulator upon cooling. Below $T_{OO}$=$T_{N}$, we detect SHG from these films and visualize the formation of AF domains with the size of several $\mu$m, which is much larger than that of phase-separated manganites. With careful examination of the magnetic point group, we can ascribe the broken symmetry to the AF spin order under the monoclinic lattice distortion concomitant with the OO, which also manifests the direction of the AF vector. [Preview Abstract] |
Wednesday, March 23, 2011 3:30PM - 3:42PM |
T17.00004: Novel Resistive Switching Behavior in Phase Separated Manganites Hangwen Guo, T. Zac Ward, Dali Sun, Paul C. Snijders, Zheng Gai, Jian Shen Electronic phase separation plays a key role in many novel phenomena in complex materials. Manganites are a prime example of this class of materials and have recently come under increase scrutiny for possible application in resistive random-access memory (RRAM) technology. Here, we will discuss our recent work on spatially confined La5/8-xPrxCa3/8MnO3. We have discovered that it is possible to drive single electronic domain formation/annihilation through electric field pulsing. By measuring the I-V curve, we find such resistive switching is different from normal RRAM mechanisms in manganites and is closely related to the nature of electronic phase separation. These findings open these systems to a new understanding of the nature of electronic phase separation and begin the development of manganites for future applications in RRAM devices. [Preview Abstract] |
Wednesday, March 23, 2011 3:42PM - 4:18PM |
T17.00005: Mesoscopic orientation-ordered percolating network in a strained manganite thin film Invited Speaker: Many unusual behaviors in complex oxides are deeply associated with the spontaneous emergence of microscopic phase separation. Recent studies on these strongly correlated materials have shown that multiple states can coexist near certain phase boundaries. In this work, a cryogenic microwave impedance microscope [1] is implemented to investigate the microscopic origin of the colossal magnetoresistance effect in manganite thin films. In a strained Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ thin film grown on (110) SrTiO$_{3}$ surface, the filamentary ferromagnetic metallic domains emergent from the antiferromagnetic charge/orbital-ordered insulating background as increasing magnetic fields align preferentially along certain crystal axes of the substrate [2]. Such an orientation ordering is missing in a relaxed sample with partial loss of the epitaxial coherency. The mesoscopic glassy orders with a period of 100nm indicate that the substrate-induced anisotropic strain rather than the Coulomb interaction plays the dominant role in the phase separation. The microwave images also revealed drastically different domain structures between the zero-field-cool and field-cool processes, consistent with the macroscopic transport measurements in both bulk and thin film materials. \\[4pt] [1] W. Kundhikanjana \textit{et al.}, arXiv 1010.1509. \\[0pt] [2] K. Lai \textit{et al.}, \textit{Science} \textbf{329}, 190 (2010). [Preview Abstract] |
Wednesday, March 23, 2011 4:18PM - 4:30PM |
T17.00006: Room Temperature Resistive Switching in Manganite Thin Films Luis Pe\~na, Luis Garzon, Zori\c{c}a Konstantinovic, Lluis Balcells, Carmen Ocal, Benjamin Martinez Resistive switching (RS), i.e. the switching between two distinct resistive states electrically controlled, is currently a subject of major interest because of its very promising properties for the implementation of data storage devices. In this work we report on the reversible transitions from low resistive (LR) to high resistivity (HR) states in high quality manganite thin films (LSMO) prepared by RF sputtering on top of (001) oriented STO substrates. The transitions between the LR and HR states are induced by the application of a bias voltage by means of the conducting tip of a scanning force microscope [1]. The experimental setup is arranged in order to avoid parasitic interfacial phenomena (e.g., metal diffusion) or electrode interconnections (e.g., filamentary formation). These RS experiments have been performed on few microns wide patterned LSMO structures. The magnetotransport properties and thermal stability of these LR and HR states are investigated in order to gain a deeper insight into the nature of the structural/electronic modifications generated by the application of high electric field by means of the AFM tip on the manganite film. \\[4pt] [1] C. Moreno et al. \textit{Nanoletters 10, 3828 (2010)} [Preview Abstract] |
Wednesday, March 23, 2011 4:30PM - 4:42PM |
T17.00007: Magnetic and Transport Properties of Heterostructured Films of Prussian Blue Analogues and Manganites P.A. Quintero, H. Jeen, E.S. Knowles, A. Biswas, M.W. Meisel, M.J. Andrus, D.R. Talham The magnetic and transport properties of heterostructured films consisting of Prussian blue analogues, $A_j$M$^{\prime}_k$[M(CN)$_6$]$_{\ell}\cdot n$H$_2$O (M$^{\prime}$M-PBA), where $A$ is an alkali ion and M$^{\prime}$,M are transition metals, and manganites have been studied. Specifically, NiCr-PBA and CoFe-PBA films\footnote{D.M.~Pajerowski \emph{et al.}, J.~Am.~Chem.~Soc. {\bf 132} (2010) 4058.} of $\sim$100~nm thickness have been deposited on perovskite (La$_{1-y}$Pr$_{y}$)$_{0.67}$Ca$_{0.33}$MnO$_3$ (LPCMO) manganese films\footnote{T.~Dhakal, J.~Tosado, A.~Biswas, Phys.~Rev.~B {\bf 75} (2007) 092404.} of $\sim$30~nm thickness. The effect of the ferromagnetic NiCr-PBA, $T_c \sim 70$~K, and the photo-controllable ferrimagnetic CoFe-PBA, $T_c \sim 20$~K, on the I-V properties of the LPCMO will be reported, where special attention will be given to the changes of the transition temperatures of the ferromagnetic metallic (FMM) and the charge-ordered insulating (COI) phases in the LPCMO substrate. \\ ** Supported by NSF DMR-0701400 (MWM), DMR-0804452 (AB), DMR-1005581 (DRT), DMR-0654118 (NHMFL), and by scholarship from the Organization of American States (PAQ). [Preview Abstract] |
Wednesday, March 23, 2011 4:42PM - 4:54PM |
T17.00008: Interfacial phase separation in La$_{2/3}$(Sr/Ca)$_{1/3}$MnO$_{3}$ thin films with different complex oxide capping layers Sergio Valencia, Zori\c{c}a Konstantinovic, Schmitz Detlef, Lluis Balcells, Benjamin Martinez Interfacial effects in sputtered manganite thin films with different capping layers (MgO, LAO, STO, NGO and Au) have been investigated. The interfaces have been chemically and magnetically characterized by means of local probes such as X-ray absorption spectroscopy (XAS) and X-ray magnetic circular (XMCD) and linear dichroism (XLD). Total electron yield detection at the Mn L-edge guarantees that the spectroscopic information originates from those regions closer to the film/capping interface. A complex phase separated scenario at the interface arises from the spectroscopic data. XAS shows departure of the Mn valence from bulk like values in case of STO and Au capping (Mn2+ presence) and in case of MgO and NGO (Mn4+ increase). XMCD shows concomitant depressed interface magnetization suggesting coexistence of ferromagnetic and non-magnetic phases. Finally XLD proves the presence of an antiferromagnetic (AFM) and orbital ordered (OO) phase. [Preview Abstract] |
Wednesday, March 23, 2011 4:54PM - 5:06PM |
T17.00009: Photoinduced effects in ferromagnetic state of manganites Vera Smolyaninova, Grace Yong, Rajeswari Kolagani, Amlan Biswas, Kilhwan Wang Rear-earth manganese oxides have a rich phase diagram. Transitions between different magnetic, electronic and structural states can be induced by application of external fields. Light-induced destruction of the charge ordering in some compositions of manganites, which results in significant increase of conductivity, is a well known example of such transition. Significant change in conductivity of these materials makes them attractive for photonic and opto-electronic device applications. We report a study of photoinduced properties of manganites in ferromagnetic metallic state. Since light penetration depth in these materials is small, thin films of manganites were used in this study. Photoinduced resistivity changes in these materials will be reported. Photoinduced effects in compositions with different temperatures of metal-insulator transition will be discussed. This work is supported by the NSF grant DMR-0348939. [Preview Abstract] |
Wednesday, March 23, 2011 5:06PM - 5:18PM |
T17.00010: Bulk-like electronic structure at the surface of epitaxial La$_{1-x}$Sr$_{x}$MnO$_{3}$ films Eric Monkman, Carolina Adamo, Daniel Shai, Dawei Shen, John Harter, Ilya Elfimov, Darrell Schlom, Kyle Shen We present direct measurements of the electronic structure of La$_{1-x}$Sr$_{x}$MnO$_{3}$ (LSMO) using a combined molecular beam epitaxy and angle-resolved photoelectron spectroscopy system. Our results allow for the first comparison between theory and experimental results over the entire Fermi surface in the ferromagnetic-metallic phase. We observe both of the predicted Fermi surface sheets, and find that the evolution of the Fermi surface shape with doping is consistent with a rigid-band shifting of the chemical potential. Measurements in the antiferromagnetic phase at x $>$ 0.5 allow us to determine the changes in the low energy electronic structure linked to the magnetic phase transition. The ability of this surface sensitive technique to probe the bulk electronic structure of LSMO limits the possible depth of a surface dead layer. This conclusion is supported by density functional theory calculations for LSMO slabs, which indicate that the polarity of the (001) surface is efficiently screened within $\sim$1 unit cell. [Preview Abstract] |
Wednesday, March 23, 2011 5:18PM - 5:30PM |
T17.00011: Hall effect on strain-released La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ thin films Liuqi Yu, Xiaohang Zhang, S. von Moln\'ar, P. Xiong, Lingfei Wang, W.B. Wu It has been demonstrated that releasing the in-plane anisotropic strain in thin films of La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ grown on orthorhombic NdGaO$_{3}$ (001) substrates can induce a charge ordering state below the Curie temperature.$^{1}$ Three LCMO films on NGO, (PLD at 735$^{o}$C and 45 Pa O$_{2}$ pressure, 45 nm thick) were annealed at 780$^{o}$C in flowing O$_{2}$ for 1, 10 and 20 hours to increase degrees of strain relaxation. Hall measurements were performed. In all three samples, the Hall resistivity takes on two distinct slopes in the paramagnetic phase: a negative slope at low fields, which varies with temperature, and a temperature-independent positive slope at high fields. Notably, the switching field for the Hall slope decreases linearly with temperature and extrapolates to the paramagnetic Curie temperatures of the samples. The observation is similar to the behavior of the nonlinear Hall effect in EuB$_{6}$ and suggests that the switches occur at a \textit{constant critical magnetization}.$^{2}$ In strain-released samples, peaks in the Hall resistivity emerge near $T_{C}$ and become more pronounced with decreasing temperature. The origins and implications of these observations will be discussed. Work supported in part by NSF DMR-0908625. $^{1}$Z. Huang et al., JAP 105, 113919 (2009) $^{2}$X. Zhang et al., PRL \textbf{103}, 106602 (2009) [Preview Abstract] |
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