Bulletin of the American Physical Society
2015 Annual Meeting of the APS Mid-Atlantic Section
Volume 60, Number 14
Friday–Sunday, October 23–25, 2015; Morgantown, West Virginia
Session C4: Material Growth and Characterization |
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Chair: David Lederman, West Virginia University Room: Waterfront Hotel Wharf AB |
Sunday, October 25, 2015 9:24AM - 10:00AM |
C4.00001: TBD Invited Speaker: Johnpierre Paglione . [Preview Abstract] |
Sunday, October 25, 2015 10:00AM - 10:12AM |
C4.00002: Multiferroic BaCoF$_{4}$ Thin Films Grown Via Molecular Beam Epitaxy Pavel Borisov, Trent Johnson, Camilo Garcia-Castro, Amit KC, Dustin Schrecongost, Cheng Cen, Aldo Romero, David Lederman Multiferroic materials exhibit exciting physics related to the simultaneous presence of multiple long-range orders, in many cases consisting of antiferromagnetic (AF) and ferroelectric (FE) orderings. To date, multiferroic fluoride compounds materials have not been studied nearly as much as oxides. In order to provide a new, promising route for fluoride-based multiferroic material engineering, we grew multiferroic fluoride BaCoF$_{4}$ in thin film form on Al$_{2}$O$_{3}$ (0001) substrates by molecular beam epitaxy. The films grow with the orthorhombic \textit{b}-axis out-of-plane and with three in-plane structural twin domains along the polar \textit{c}-axis directions. The FE ordering in thin films was verified by FE remanent hysteresis loops measurements at $T=14$ K and by room temperature piezoforce microscopy (PFM). An AF behavior was found below Neel temperature $T_{N}= 75$ K, which is in agreement with the bulk properties. At lower temperatures two additional magnetic phase transitions at 19 K and 41 K were found. First-principles calculations demonstrated that the growth strain applied to the bulk BaCoF$_{4}$ indeed favors two canted spin orders, along the \textit{b}- and \textit{a}-axes, respectively, in addition to the main AF spin order along the \textit{c}-axis. [Preview Abstract] |
Sunday, October 25, 2015 10:12AM - 10:24AM |
C4.00003: \textbf{Self-sustained current oscillations in NbO}$_{\mathrm{\mathbf{2}}}$\textbf{ thin film vertical devices grown on TiN coated SiO}$_{\mathrm{\mathbf{2}}}$\textbf{/Si substrates using pulsed laser deposition } Toyanath Joshi, Pavel Borisov, David Lederman Due to its relatively high MIT temperature (1081 K) and current-controlled negative differential resistance, NbO$_{\mathrm{2}}$ is a robust candidate for memory devices and electrical switching applications. Highly stable and self-sustained current oscillations can be generated in NbO$_{\mathrm{2}}$ thin films when attached to a constant voltage source. In this work, we present the self-sustained current oscillatory behavior of NbO$_{\mathrm{2}}$ thin film vertical devices grown on TiN coated SiO$_{\mathrm{2}}$/Si substrates using pulsed laser deposition (PLD). The formation of NbO$_{\mathrm{2}}$ phase was confirmed by Grazing Incidence X-ray Diffractometry (GIXRD), X-ray Photoelectron Spectroscopy (XPS) and current vs. voltage measurements. Probe station tips (tip size \textasciitilde 2$\mu $m) and TiN bottom layer were used as top and bottom contacts. Current pulse measurements, performed in response to applied triangular voltage pulses, showed a non-linear threshold switching behavior for voltage pulse durations of 100 ns and above. Self-sustained current oscillatory behavior was obtained with frequencies ranging from 5 to 12.5 MHz from the film grown in lower (1 mTorr) and 10.5 - 14.8 MHz from the film grown in higher (10 mTorr) O$_{\mathrm{2}}$/Ar mixed growth pressure (\textasciitilde 7{\%} O$_{\mathrm{2}})$ while changing V$_{\mathrm{pp}}$ of the rectangular pulse voltage from 5 -- 12.5 V and 10.5 -- 14.8 V respectively. [Preview Abstract] |
Sunday, October 25, 2015 10:24AM - 10:36AM |
C4.00004: Characterization of ferromagnetic $\tau $ -MnAl thin films grown by MBE James Kally, David Rench, Kun-Hua Tu, Danielle Reifsnyder Hickey, Jong Seok Jeong, Ryan Wu, Andre Mkhoyan, Caroline Ross, Nitin Samarth The epitaxial stabilization of MnAl thin films in the $\tau $-phase (tetragonal crystal structure) results in a metallic ferromagnet with a strong uniaxial out-of-plane magnetic anisotropy. The ensuing perpendicular magnetic anisotropy makes these films potentially attractive for energy efficient, high density magnetic memory applications. These thin films are also of contemporary interest for semiconductor spintronics since they can be integrated with III-V semiconductor devices. We describe the epitaxial growth of $\tau $-MnAl films on GaAs (001), as well as the characterization of their structural, magnetic and transport properties. Thin films of $\tau $-MnAl are prepared by molecular beam epitaxy at 250 \textordmasculine C. High-resolution transmission electron microscopy images show a well-ordered crystal while energy dispersive spectroscopy confirms stoichiometric control of the composition. Magnetometry measurements reveal a very high coercivity of 10 kOe, a saturation magnetization of 400 emu/cc and a uniaxial magnetic anisotropy constant $K_{\mathrm{u\thinspace }}=$10 Merg/cc. Further, we demonstrate a route for nanopatterning $\tau $-MnAl films into pillars of sub-100 nm scale diameter. [Preview Abstract] |
Sunday, October 25, 2015 10:36AM - 10:48AM |
C4.00005: Growth, structural, dielectric and magnetic properties of epitaxial multiferroic NaMnF$_{3}$ thin films Amit KC, Pavel Borisov, David Lederman Epitaxial NaMnF$_{3}$ thin films were grown on SrTiO$_{3\, }$(100) single crystal substrates via molecular beam epitaxy (MBE). The orthorhombically distorted perovskite fluoride NaMnF$_{3}$ (\textit{Pnma} space group) has been predicted to have a polar instability at low temperatures due to MnF$_{6}$ octahedral tilts. Structural, magnetic and dielectric properties were studied. Thin film structural quality as a function of the substrate temperature and film thickness was investigated using X-ray diffraction (XRD), in-situ reflection high-energy electron diffraction (RHEED), and atomic force microscopy (AFM). The best films were smooth and single phase grown with three different twin domains. Magnetic characterization was performed using superconducting quantum interference device (SQUID) magnetometry. In-plane magnetization measurements revealed antiferromagnetic ordering with a Neel temperature $T_{N}_{\, }=$ 66 K. For the dielectric studies, NaMnF$_{3}$ films were grown on top of SrRuO$_{3}$ (100) buffer layers grown via pulsed laser deposition that were used as bottom electrodes. Dielectric spectroscopy was performed at different temperatures between 11K and room temperature in a frequency range 1 Hz to 100 kHz. Significant temperature dependent dielectric properties were observed. [Preview Abstract] |
Sunday, October 25, 2015 10:48AM - 11:00AM |
C4.00006: \textbf{Ferroelectricity and Persistent Photocurrent in NaMnF}$_{\mathrm{\mathbf{3}}}$\textbf{ Thin Film} Ming Yang, Amit KC, Pavel Borisov, David Lederman, Aldo Romero, Cheng Cen Abstract: While studies of complex oxides have yielded many fascinating phenomena based on electron correlation effects, there are strong indications that complex fluorides may have analogous, or even enhanced properties. NaMnF$_{\mathrm{3}}$ is one such example, where multiferroic characters and magnetoelectric coupling have recently been predicted theoretically. Thin films of NaMnF$_{\mathrm{3}}$ with 50 nm thickness were grown on SrTiO$_{\mathrm{3}}$ substrates via molecular beam epitaxy. Ferroelectric properties of NaMnF$_{\mathrm{3}}$ were studied by piezoelectric force microscopy. Stable ferroelectric switching were obtained at room temperature by biased scanning probe. In addition, the sample also exhibits an interesting coupling between its out-of-plane polarization and in-plane electric field applied. At low temperatures, photocurrent was observed under 400 nm laser illumination. Amplitude and direction of such photocurrent can be hysterically controlled by external biases. This phenomenon likely results from the combined effects of built-in field in ferroelectrically polarized NaMnF$_{\mathrm{3}}$ thin film and the photocarriers generated in SrTiO$_{\mathrm{3}}$ substrate. These findings indicate great potential of complex fluorides in applications such as ferroelectric capacitors, switches, and memory devices. [Preview Abstract] |
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