Showing papers by "Tae Won Noh published in 1997"
TL;DR: In this article, the conductivity spectra of manganese oxides were measured in a wide photon energy region between 5 meV and 30 eV at room temperature and the Hund exchange energy was found to be about 3.4 eV and the Jahn-Teller stabilization energy was less than 0.5 eV.
Abstract: Reflectivity spectra of ${\mathrm{CaMnO}}_{3}$ and ${\mathrm{LaMnO}}_{3}$ were measured in a wide photon energy region between 5 meV and 30 eV at room temperature. Using the conductivity spectra obtained from the Kramers-Kronig analysis, electronic structures of the manganese oxides were investigated. In particular, the states near the Fermi energy ${\mathrm{E}}_{\mathrm{F}}$, O 2p and Mn 3d (${\mathrm{e}}_{\mathrm{g}}$,${\mathrm{t}}_{2\mathrm{g}}$), were studied in detail. It was found that the O 2p band is located closer to ${\mathrm{E}}_{\mathrm{F}}$ than the Mn ${\mathrm{t}}_{2\mathrm{g}}$ band. For ${\mathrm{LaMnO}}_{3}$, the filled Mn ${\mathrm{e}}_{\mathrm{g}\mathrm{\ensuremath{\uparrow}}}^{1}$ band is located closer to ${\mathrm{E}}_{\mathrm{F}}$ than any other valence band. The ${\mathrm{t}}_{2\mathrm{g}}$-${\mathrm{e}}_{\mathrm{g}}$ Hund exchange energy was found to be about 3.4 eV and the Jahn-Teller stabilization energy ${\mathrm{E}}_{0}$ was estimated to be less than 0.5 eV.
126 citations
TL;DR: In this article, a La0.7Sr0.3MnO3−δ (LSMO) film was fabricated on SiO2/Si(001) substrates using a Bi4Ti3O12 (BTO) template layer.
Abstract: c-axis textured La0.7Sr0.3MnO3−δ (LSMO) films were fabricated on SiO2/Si(001) substrates using a Bi4Ti3O12 (BTO) template layer. Electrical and magnetic properties of LSMO were investigated. The LSMO/BTO layer of this structure has no in-plane alignment. Even though a ferromagnetic transition temperature, TC, is as high as that of the epitaxial LSMO film (360 K), a resistivity peak temperature, TP, is about 140 K lower than TC. The resistivity behavior as a function of temperature for LSMO/BTO/SiO2/Si films is found to be dominated by grain boundary effects. Low field sensitive magnetoresistance which suggests spin tunneling through the grain boundaries is also observed at room temperature.
53 citations
TL;DR: In this article, the Pb(Zr,Ti)O3 (PZT) thin films with different electrode configuration were grown on LaAlO3 substrates by pulsed laser deposition (PLD).
Abstract: (La,Sr)CoO3/Pb(Zr,Ti)O3/(La,Sr)CoO3 (LSCO) heterostructures have been grown on LaAlO3 substrates by pulsed laser deposition (PLD) to investigate asymmetric polarization switching of Pb(Zr,Ti)O3 (PZT) thin films with different electrode configuration. P-V hysteresis loop of LSCO/PZT/LSCO was symmetric. However, LaCoO3 (LCO)/PZT/LSCO showed a largely asymmetric P-V hysteresis loop and large relaxation of the remanent polarization at the negatively poled state, which means that the negatively poled state was unstable. On the other hand, LSCO/PZT/LCO exhibited large relaxation of the positively poled state. The asymmetric behavior of the polarized states implies the presence of an internal electric field inside the PZT layer. It is suggested that the internal electric field caused by built-in voltages at LCO/PZT and LSCO/PZT interfaces. The built-in voltages at LCO/PZT and LSCO/PZT interfaces were 0.6 eV and 2.1 eV, respectively.
17 citations
TL;DR: In this paper, an epitaxial Bi4Ti3O12(BTO) thin film was deposited on MgO(001) substrates by pulsed laser deposition and X-ray diffraction patterns showed that the c-axes of BTO films are oriented normal to the substrate surface.
Abstract: Using La0.5Sr0.5CoO3(LSCO) or Pt film as a bottom electrode layer, epitaxial Bi4Ti3O12(BTO) thin films were deposited on MgO(001) substrates by pulsed laser deposition. X-ray diffraction patterns showed that the c-axes of BTO films are oriented normal to the substrate surface. Interestingly, an epitaxial Pt/BTO/Pt film showed a strongly preferred polarization state directed towards the top electrode in spite of the symmetric electrode configuration. The inprint state did not change significantly in the pulse test with DC bias. These anomalous behaviors suggest that the imprint characteristic is highly correlated with interfacial states between the electrodes and the BTO films. To understand space charge effects in the metal-ferroelectric contacts, imprint characteristics of the thin film capacitors with various top electrodes were investigated. Auger Electron Spectroscopy(AES) depth profile was measured, to check the possibility of a interdiffusion of the bottom electrode with the BTO layer. Inte...
2 citations
TL;DR: In this paper, the LSMO layer in a LSMO/SrTiO3/YBa2Cu3O7/MgO heterostructure is found to have coherent in-plane grain boundaries with a predominance of 45° rotations (between [100] and [110] grains) in addition to the cube-on-cube epitaxial relationship.
Abstract: C-axis oriented La0.7Sr0.3MnO3.δ (LSMO) films were fabricated on the top of SrTiO3/YBa2Cu3O7 grown on MgO(001) substrates. From x-ray φ-scan and planar transmission electron microscopy measurements, the LSMO layer in the LSMO/SrTiO3/YBa2Cu3O7/MgO heterostructure is found to have coherent in-plane grain boundaries with a predominance of 45° rotations (between [100] and [110] grains) in addition to the cube-on-cube epitaxial relationship. Also, epitaxial LSMO/Bi4Ti3O12/LaAl03 (001) and c-axis textured LSMO/Bi4Ti3O12/SiO2/Si(001) with random in-plane grain boundaries are introduced as the counterparts for comparison. The resistivity and magnetoresistance (MR) of LSMO layer were measured and compared in these three different heterostructures. The low field MR at low temperature shows a dramatic dependence on the nature of the grain boundary. An attempt is made to interpret these results on the basis of correlation between the magnetic properties and grain structures.
2 citations
TL;DR: In this paper, an asymmetric band diagram for the Pt/BTO/Pt structure was suggested, and the imprint failure can be explained by existence of asymmetric interracial states.
Abstract: Epitaxial Bi4Ti3012 (BTO) films with Lao0.5Sr0.5Co03 (LSCO) or Pt bottom electrodes were grown on MgO(OOl) substrates by pulsed laser deposition. Surprisingly, a symmetric Pt/BTO/Pt capacitor showed a highly asymmetric polarization switching and an asymmetric Pt/BTO/LSCO capacitor revealed a nearly symmetric polarization switching. To understand these intriguing phenomena, Auger electron spectroscopy and x-ray photoemission spectroscopy depth-profiles were used. The evidences for interdiffusions at the bottom BTO/Pt interface were found. To get further understanding on the interfacial states, a capacitance-voltage (C-V) measurement was performed on the Pt/BTO/Pt capacitor. By fitting the C-V data with a back-to-back Schottky diode model, built-in voltages at the top and the bottom interfaces were determined to be 1.1 V and 3.2 V, respectively. From the obtained built-in voltages, an asymmetric band diagram for the Pt/BTO/Pt structure was suggested. Therefore, the imprint failure can be explained by existence of asymmetric interracial states.