Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session N20: Focus Session: Complex Oxide Thin Films Surfaces and Interfacess III: New Materials, New Techniques, and Effects of Strain |
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Sponsoring Units: DMP GMAG Chair: Anand Bhattacharya, Argonne National Laboratory Room: Baltimore Convention Center 317 |
Wednesday, March 15, 2006 8:00AM - 8:12AM |
N20.00001: Growth and Properties of a New Correlated Electron Perovskite Thin Film -- PbVO$_{3}$ . Lane W. Martin, Qian Zhan, Wenkan Jiang, Miaofang Chi, Nigel Browning, Yuri Suzuki, R. Ramesh We report the growth of single phase, fully epitaxial thin films of a relatively new perovskite material, lead vanadate (PbVO$_{3})$, using pulsed laser deposition. This growth realizes the first production of PbVO$_{3}$ outside of high-temperature and high-pressure techniques through growth of epitaxial thin films on various substrates. Structural analysis of the PbVO$_{3}$ thin films using transmission electron microscopy, x-ray diffraction, and Rutherford backscattering spectroscopy reveals films that are single phase, highly crystalline, and have a tetragonally distorted perovskite structure, with $a$ = 3.79{\AA} and $c$ = 5.02{\AA} (c/a = 1.32). Electron energy loss spectroscopy and x-ray absorption spectroscopy were used to show the stabilization of vanadium in the V$^{4+}$ state, thereby proving the creation of a new $d^{1}$ system for intensive physical study. Films exhibit semiconducting behavior in plane of the film with thermally activated behavior and distinctly different properties from other $d^{1}$ $A$VO$_{3}$ thin films. Studies of the magnetic and ferroelastic/ferroelectric nature of PbVO$_{3}$ are also underway. [Preview Abstract] |
Wednesday, March 15, 2006 8:12AM - 8:24AM |
N20.00002: Phase Transitions of SrFeO$_{3}$ Studied Using a Single-Crystalline Film Naoaki Hayashi, Shigetoshi Muranaka, Takahito Terashima, Mikio Takano To study the electronic nature of SrFeO$_{3}$ (SFO), which is a cubic perovskite containing Fe$^{4+}$ equipped with deep $d$ levels and is, therefore, dominated by $p$-hole character, a single crystalline film was grown and the resistivity (\textit{$\rho $}), Hall effect, magnetoresistance (\textit{MR}) and susceptibility were measured. It is known that this oxide in bulk form becomes antiferromagnetically ordered in a screw spin structure. The $T_{N}$ of the film has been found to be at 120$\sim $125 K from the susceptibility measurement, while the transport properties showed well-defined anomalies at 105 K, rather than at the $T_{N}$. The metallic film (\textit{$\rho $} = 9$\times $10$^{-4} \quad \Omega $cm at 300 K) exhibited a hysteretic, inflectional drop in the \textit{$\rho $} -$T $curve at 105 K after showing a very small anomaly at 125 K; the Hall coefficient was positive and temperature-independent above 110 K but increased quickly below $\sim $100 K; the \textit{MR} changed its sign from negative to positive quite steeply at 105 K. Considering these results together with what is known about bulk samples, we conclude that SFO undergoes its antiferromagnetic transition in two stages, passing an incompletely coherent stage before entering the final coherent state. [Preview Abstract] |
Wednesday, March 15, 2006 8:24AM - 8:36AM |
N20.00003: Magnetic Properties of PLD Grown Expitaxial Double Perovskite Thin Films D.E. Brown, S. Totapally, Y. Yoo, S. Kolesnik, J. Mais, O. Chmaissem, J. Churilla, B. Dabrowski, C. Kimball, M. Haji-Sheik Transition metal oxides with a double perovskite structure A$_{2}$FeMoO$_{6}$ and (A = Ca, Ba, Sr) has attracted a great deal of attention owing to their high magnetic transition temperatures and spin dependent transport properties. Electronic structure calculations and experimental results show that these materials are half-metallic ferrimagnets with localized up-spin electrons on the Fe ions and itinerant down-spin electrons shared between Fe and Mo. The Fe and Mo atoms are ordered on alternating, corner-shared octahedral sites, however, the ordered array can have imperfections that are dependent upon synthesis conditions. We have grown, using a pulsed laser deposition device, epitaxial double perovskite thin films. These films have been characterized by SQUID, resistivity, and x-ray crystallography measurements. The measurements show that double perovskite thin films can be grown with a high degree of order between the Fe and Mo atoms. Thus these materials can be attractive candidates for spin electronic devices. [Preview Abstract] |
Wednesday, March 15, 2006 8:36AM - 8:48AM |
N20.00004: Exotic Single Crystal Thin Films Made From Cobalt Ferrite. H. Corcoran, A. Coleman, A. Lisfi, C. M. Williams, W. Morgan, A. Kumar The search for new magnetic materials is driven by technological demands such as increasing the magnetic recording density. Materials possessing a large magnetic anisotropy are suitable media to meet such requirements since a stable magnetization can be promoted in nano-structures. Hard ferrites such as the hexagonal (BaFe$_{12}$O$_{19})$ and the cubic (CoFe$_{2}$O$_{4})$ are attractive for such kind of applications due to their large magnetocrystalline anisotropy and high chemical stability. In this talk we report on exotic properties of films made from CoFe$_{2}$O$_{4}$. Epitaxial CoFe$_{2}$O$_{4}$ thin films have been grown by pulsed laser deposition (PLD) on (100) MgO substrate. Two types of spin-reorientation have been observed in such films upon annealing or increasing the film-thickness. In the as-deposited layers and at low thickness the easy axis of the magnetization is confined to the normal to the film plane whereas at large thickness the film plane becomes the preferential direction of the magnetization. On the other hand annealing induces a reorientation of magnetic anisotropy, which switches from the normal to the film plane in the as-deposited film to be in-plane aligned in the annealed state. The origin of both reorientations is explained in term of competition between stress and magnetocrystalline anisotropies. [Preview Abstract] |
Wednesday, March 15, 2006 8:48AM - 9:00AM |
N20.00005: Magnetic Anisotropy of Cr-Substituted Magnetostrictive Cobalt Ferrite Yevgen Melikhov, John Snyder, Chester Lo, Paul Matlage, Sang-Hoon Song, Kevin Dennis, David Jiles In order to tailor the magnetomechanical response of substituted cobalt ferrite for strain sensing and actuating applications, more needs to be known about the variation of the basic magnetoelastic and magnetic properties with temperature and composition. In this study, the variation of magnetic anisotropy with temperature and composition for a series of Cr-substituted cobalt ferrites, CoCr$_{x}$Fe$_{2-x}$O$_{4}$, (0$\le $x$\le $0.8) was investigated. In order to determine the cubic anisotropy constant $K_{1, }$the ``high field'' regime (from 1 T to 5 T) of the major magnetic hysteresis loops, which were measured at temperatures over the range 10-400 K using a SQUID magnetometer, was fitted using the law of approach approximation $M(T)=M_{S}$(1-8/105$K_{1}^{2}$/\textit{($\mu $}$_{0}$\textit{HM}$_{S})^{2})$ plus a forced magnetization term linear in applied field $H$. It was found that anisotropy increases with decreasing temperature, with the steepest increase coming at progressively lower temperatures for increasing Cr content. For fixed temperatures, anisotropy decreases with increasing Cr content. For the pure cobalt ferrite and x=0.2 Cr samples it appears that for temperatures less than 150 K, 5 Tesla is not enough to saturate the samples, so anisotropy cannot be computed correctly by this method. This research was supported by NSF, Grant No.DMR-0402716, and by NASA, Award No.NAG-1-02098. [Preview Abstract] |
Wednesday, March 15, 2006 9:00AM - 9:12AM |
N20.00006: Influence of substrate strain on (La$_{1-x}$Pr$_{x})_{1-y}$Ca$_{y}$MnO$_{3}$ phase transition Dane Gillaspie, J.X. Ma, H-Y. Zhai, Z. Ward, E.W. Plummer, H. Christen, J. Shen The large-scale phase separation between ferromagnetic metallic (FMM) and charge-ordered insulating (COI) domains observed in (La$_{1-x}$Pr$_{x})_{1-y}$Ca$_{y}$MnO$_{3}$ (LPCMO) crystals has attracted a lot of attention. This coexistence of phases is very sensitive to structural and magnetic changes, and is responsible for the enhanced magnetoresistance in LPCMO compared to its parent compounds. The energy balance of the FMM and COI phases is still not well understood. We can change the energy balance by changing the substrate, and therefore the strain on the thin film, and thereby improve our understanding of the phase transition. We have grown and characterized several different thicknesses of LPCMO on LaAlO$_{3}$, SrLaGaO$_{4}$, NdGaO$_{3}$ and SrTiO$_{3}$ substrates. We have observed that the compressive strain from the LaAlO$_{3}$ substrate suppresses the long-range charge ordering in the sample, and enhances magnetoresistance and magnetic hysteresis. The charge ordering is also suppressed in the films on SrLaGaO$_{4}$, even though the strain is negligible. Conversely, the tensile strain from the NdGaO$_{3}$ and SrTiO$_{3}$ substrates enhances the long-range charge ordering and reduces the magnetoresistance and magnetic hysteresis. *Oak Ridge National Laboratory, managed by UT Battelle for the U.S. Dept. of Energy under contract DE-AC05-00OR22725 [Preview Abstract] |
Wednesday, March 15, 2006 9:12AM - 9:24AM |
N20.00007: The role of strain in the magnetic properties of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films studied by magnetic force microscopy Ravi Kummamuru, Yeong-Ah Soh, Neil Mathur, Luis Hueso In order to elucidate the role of strain in the magnetic properties of manganite films, we studied the behavior of the magnetic domains in La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) films grown on SrTiO$_{3}$ (STO) and NdGaO$_{3}$ (NGO) substrates, which are differently strained. Our previous studies on the magnetic properties of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films grown on STO substrates using magnetic force microscopy showed a distinct magnetic texture within magnetic domains, and spin reorientation and enhancement of T$_{C}$ near grain boundaries. These results were attributed to the strain in the film caused by the lattice mismatch with the substrate and the strain relaxation at the grain boundaries. Our new studies on La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films grown on NGO substrates, which have very low strain due to a close lattice match between the film and substrate, show no presence of magnetic texture and a very sharp transition from the paramagnetic to ferromagnetic phase. [Preview Abstract] |
Wednesday, March 15, 2006 9:24AM - 9:36AM |
N20.00008: Strain Induced Crystal Superstructure in Manganite Films Yeong-Ah Soh, Zahirul Islam, Jonathan Lang, George Srajer, Neil Mathur, Mark Blamire Using xray diffraction we studied in detail the crystal structure of a 100 nm thick La$_{0.7}$ Sr$_{0.3 }$MnO$_{3}$ film grown on a SrTiO$_{3}$ substrate. Satellite peaks are observed at ($H \quad \pm \quad \delta h$, $K$, $L)$ for nonzero $K$ and ($H$, $K \quad \pm \quad \delta k$, $L)$ for nonzero $H$. No satellite peaks are observed around (0 0 $L)$ reflections. Our measurements show that the modulation wave vectors and polarization vectors representing the atomic displacements are perpendicular to each other and point in the direction parallel to the plane of the film. $L$ scans around the main Bragg peaks and around the satellite peaks exhibit strong Laue oscillations indicating that the superstructure is coherent throughout the whole thickness of the film. We will discuss the results of the xray measurements in connection with the scanning probe microscopy measurements done on the same film. [Preview Abstract] |
Wednesday, March 15, 2006 9:36AM - 9:48AM |
N20.00009: Electronic properties of structural twin and antiphase boundaries in materials with strong electron-lattice couplings K. H. Ahn, T. Lookman, A. Saxena, A. R. Bishop Using a symmetry-based atomic scale theory of lattice distortions, we show that in functional materials with strong electron lattice coupling, the electronic properties are distinctly modified near elastic textures such as twin boundaries (TBs) and antiphase boundaries (APBs), which can be directly measured by STM. The results also show that the heterogeneities of electron local DOS are not confined within TBs and APBs, but can propagate into domains in the form of Friedel oscillations for TBs and with the wave vector related to short wave length lattice distortions for APBs. The results are discussed in relation with perovskite manganites and other functional electronic materials. Reference: Ahn, Lookman, Saxena, and Bishop, Phys. Rev. B 71, 212102 (2005). [Preview Abstract] |
Wednesday, March 15, 2006 9:48AM - 10:00AM |
N20.00010: Ultra-thin Perovskite Manganite films on SrTiO$_{3}$ and SrTiO$_{3}$/Si heterostructures A. Pradhan, D. Hunter, K. Zhang, B. Lasley, K. Lord, T.M. Williams, R.R. Rakhimov We report on the growth and characterization of high-quality ultra-thin La$_{0.7}$Ba$_{0.3}$MnO$_{3}$ and La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ epitaxial films on SrTiO$_{3}$ and SrTiO$_{3}$-buffered Si (100) and Si (111) substrates by pulsed-laser deposition. The films demonstrate remarkable magnetic and electrical properties associated with the colossal magnetoresistance behavior at and above room temperature. The enhanced transition temperature of manganite films on buffered Si substrates is discussed in terms of the strain relaxation at the interface between the manganite film and the SrTiO$_{3}$ buffer layer which is caused by the smaller grain size. We also report the doping of Ru (x=0.3 to 0.4) into Mn sites in LSMO films grown both on STO and STO buffered Si. The films display remarkable hardening of $H_{c}$ due to the charge-transfer-enhanced exchange coupling. We have optimized doping for the compensation of hole doping by the valence effect of Ru,. This effect has been explained in terms of the charge transfer between the Mn$^{4+}$ and Ru$^{4+}$ species and ferromagnetic interaction between the resultant Mn$^{3+}$ and Ru$^{5+/4+}$. The electrons in Ru$^{4+}$ partially occupy the degenerated $t_{2g}$ orbitals due to the fact that Ru is a heavy metal, we expect a single-ion anisotropy of Ru spins through a spin-orbit channel. This structure is highly applicable for fabrication of the magnetic tunnel junctions. [Preview Abstract] |
Wednesday, March 15, 2006 10:00AM - 10:12AM |
N20.00011: Variation of magnetic domain structure correlated to low-field magnetoresistance hysteresis in La$_{0.66}$Ca$_{0.34}$MnO$_{3}$ film as observed by magnetic force microscopy. Changbae Hyun, Casey Israel, Weida Wu, Alex de Lozanne, Alaka P. Valanju, Rodger M. Walser, M.E. Gomez, J. G. Ramirez, G.A. Mendoza The ferromagnetic domain structure of a 150-nm-thick La$_{0.66}$Ca$_{0.34}$MnO$_{3}$ film was imaged by magnetic force microscopy (MFM) as a function of in-plane applied field at 240K, just below T$_{C}$. The film was grown by sputtering on a (001) SrTiO$_{3}$ substrate. The variation of the domain structure is correlated with the hysteresis in both magnetization and magnetoresistance. The resistance peak in the magnetoresistance coincides with the coercivity of the film and sweeping changes in the MFM images. We show the effect of applying the in-plane magnetic field along both in-plane crystalline axes. [Preview Abstract] |
Wednesday, March 15, 2006 10:12AM - 10:24AM |
N20.00012: Anisotropic magnetoresistance in colossal magnetoresistive La$_{1-x}$Sr$_{x}$MnO$_{3}$ thin films Jeng-Bang Yau, X. Hong, C. H. Ahn, Y. Bason, L. Klein We report on magnetic field and temperature dependent measurements of the anisotropic magnetoresistance (AMR) in epitaxial La$_{1-x}$Sr$_{x}$MnO$_{3}$ (LSMO) thin films. While in $3d$ ferromagnetic alloys increasing the magnetization, either by reducing the temperature or increasing the magnetic field, increases the AMR, in LSMO films the AMR dependence on magnetization displays non-monotonic behavior which becomes particularly pronounced in lightly doped compounds. This could imply that these samples may be electronically inhomogeneous, in which increased magnetization yields enhanced uniformity which suppresses spin-dependent scattering and hence reduces the AMR. [Preview Abstract] |
Wednesday, March 15, 2006 10:24AM - 10:36AM |
N20.00013: Size effect in percolative phase separation of colossal magnetoresistive (La,Pr,Ca)MnO$_{3}$ films . Hong-Ying Zhai, Jianxing Ma, Dane Gillaspie, Thomas Ward, Anthony Hmelo, Leonard Feldman, Jian Shen La$_{1-x-y}$Pr$_{y}$Ca$_{x}$MnO$_{3}$(LPCMO) (where x=3/8) is electronically phase-separated into a sub-micrometre-scale mixture of ferromagnetic metallic (FMM) and charge-ordered insulating (COI) domains. Transport through the ferromagnetic network depends sensitively on the domain structure, which can be controlled by magnetic field, light, and strain, etc. Enhanced CMR effect can be achieved in the vicinity of the percolative threshold. Using optical lithography, e-beam lithography, and focused ion beam techniques, we can fabricate series micron and sub-micron structures on LPCMO films grown on LaAlO$_{3}$ and SrTiO$_{3}$ using pulsed laser deposition. Size dependant transport properties will be addressed in detail. Research sponsored by the U.S. Department of Energy under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory. [Preview Abstract] |
Wednesday, March 15, 2006 10:36AM - 10:48AM |
N20.00014: Combinatorial Hall Effect System for Oxide Films Jeffrey Clayhold, Bryan Kerns, David Rench, Michael Schroer, Ivan Bozovic Combinatorial film growth techniques have made it possible to produce large numbers of high-quality oxide films at one time. Characterizing the samples by traditional methods would be far too slow. Certain measurements, such as the the Hall effect, require careful temperature control and lock-in amplifiers to resolve the small signal. We have built special-purpose, multi-channel resistance bridges to measure the Hall effect simultaneously in 32 samples. The voltage resolution is less than 2 nV for signals on the order of 1 $\mu$V, for a signal-to-noise ratio of 500. We will discuss Hall effect data from samples of La$_{\rm 2-x}$Sr$_{\rm x}$CuO$_{\rm 4}$. [Preview Abstract] |
Wednesday, March 15, 2006 10:48AM - 11:00AM |
N20.00015: B-site substitution in LaTiO$_{3}$ thin films: influence on the titanium oxidation state. A. Guiller, C. Marchiori, M. Sousa, R. Germann, J. P. Locquet, J. Fompeyrine, J. W. Seo LaTiO$_{3}$ (LTO) is a Mott insulator, antiferromagnetic at RT, and exhibits a Metal Insulator Transition (MIT) at the Neel temperature. Despite its complex chemistry, it is an interesting candidate to fabricate field-effect devices. A full device requires the deposition of a dielectric in contact with the LTO thin film such as HfO$_{2}$. This choice will be discussed, and we will present issues related to a possible interdiffusion. Adding Hf in the LTO layer leads to a clear change of the resistivity measured as a function of temperature, and strongly influences the MIT temperature. Starting from a semiconducting LTO, 20{\%} Hf substitution on the perovskite B-site makes the layer become metallic from RT down to 4.2K. The average valence of Ti is increasing from Ti$^{3+}$ towards Ti$^{4+}$ with the substitution of Hf, as shown by XPS. Several explanations can be proposed beyond a real incorporation of Hf into the LTO matrix. Besides a pure electronic effect, structural and catalytic effects have been then investigated in details by means of XRD, XPS and HRTEM. Multilayers as well as single-phase thin films have been fabricated to disentangle these different effects. Our results will be discussed taking also into account a possible material loss in the structure. We will in particular explore the behavior of La-deficient structure to qualitatively explain our data. [Preview Abstract] |
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