Multifunctional Oxides: Session III
Sponsored by: MS&T Organization
Program Organizers: Xiaoqing Pan, University of Michigan

Tuesday 2:00 PM
October 18, 2011
Room: E162A
Location: Greater Columbus Convention Center

Session Chair: Chonglin Chen, UTSA

2:00 PM  Invited
Heterostructured Titania/Ferroelectric Catalysts for Water Splitting: Li Li¹; Andrew Schultz¹; Yiling Zhang¹; Paul Salvador¹; Gregory Rohrer¹; ¹Carnegie Mellon University
    In this talk, we will describe photochemical reactions on thin titania films supported by ferroelectric substrates (BaTiO3 and BiFeO3) with a wide range of orientations. For all of the orientations and both phases of titania, the thinnest films have reactivities equal to or greater than the bulk-like films, suggesting that the charge separating characteristics of the substrate have the potential to increase the reactivity of titania. When titania is supported by the narrower bandgap ferroelectric BiFeO3, photochemical reactions on the titania surface can be stimulated by visible light with an energy smaller than titania’s bandgap. Finally, the efficacy of the dipolar field effect is demonstrated by measurements of hydrogen evolution rates from a composite catalyst micron sized comprised of SrTiO3 or BaTiO3 particles coated with mesoporous titania. The rate of hydrogen evolution from the composite catalyst exceeds the rate of hydrogen evolution from the BaTiO3 or the mesoporous titania alone.

2:40 PM
High Frequency Magnetodielectric Properties of Hexagonal Ferrites: Yajie Chen¹; Trifon Fitchorov¹; Bolin Hu¹; Anton Geiler¹; Carmine Vittoria¹; Vincent Harris¹; ¹Northeastern University
    Hexagonal ferrites are vital for a wide range of high frequency applications where sending, receiving, and manipulating electromagnetic signals are important. We present here results of the design and processing of microwave magnetic materials for high frequency applications (i.e. 1-20 GHz), with emphasis on the doped Ba-hexaferrites. Scandium or Indium ions are used to reduce the magnetocrystalline anisotropy field in BaFe12O19 while retaining an easy magnetization axis along the crystallographic c-axis. The work is primarily focused on In-doped BaFe12O19 ferrite ceramics, which were examined for electric, magnetic, ferromagnetic resonance, and magnetodielectric properties. In pursuit of lower operating frequencies, the experiments demonstrate the ability to tailor the magnetocrystalline anisotropy field with the substitution of indium for iron. We demonstrate for the first time magnetic tuning of dielectric properties at room temperature and under low magnetic fields. The results offer potential for use in next generation multifunctional microwave devices.

3:00 PM Break

3:20 PM  Invited
Magnetism and Electronic Structure of Eu²⁺ Perovskite Oxides: Hirofumi Akamatsu¹; ¹Kyoto University
    Cubic perovskite EuTiO₃ has recently attracted considerable attention due to its strain-induced multiferroicity. Previous first-principles studies have revealed that it is critically balanced between the antiferromagnetic and ferromagnetic states. The microscopic mechanism behind its cell-volume-dependent magnetism, however, remains to be clarified. In this study, the magnetic interactions and electronic structure in EuMO₃ (M=Ti, Zr, Hf, Si, and Ge) and Eu₂TiO₄ have been systematically investigated using hybrid Hartree-Fock density functional calculations. It is shown that antiferromagnetic superexchange interactions between Eu-4f spins via nonmagnetic B-site cations such as Ti⁴⁺ ions play a crucial role in the magnetism of EuMO₃ (M=Ti, Zr, and Hf). In addition, the magnetic, structural, and optical properties of EuMO₃ (M=Ti, Zr, and Hf) have been investigated experimentally. The magnetic ground state, lattice constants, and band gap are in good agreement with those obtained by the calculations.

4:00 PM
Anomalous Magnetic Behavior of Cobalt Doped Sm2O3 Thin Films: Nathan Gray¹; Ashutosh Tiwari¹; ¹University of Utah
    In this talk, we will report the observation of a new kind of magnetism in precipitate free cobalt doped Sm₂O₃ thin films. High quality thin films of Sm_1.9Co_0.1O₃ were prepared by pulsed laser deposition and thoroughly characterized using several techniques of structural characterization and magnetic property measurements. We found that these films exhibit a magnetic phenomenon which cannot be accounted for by conventional models. We termed the observed magnetic response Dynamic Superparamagnetism. The observed behavior appears quite similar to that observed in classical superparamagnetic systems, however it has a different temperature dependence and unique origin. Our proposed model for Dynamic Superparamagnetism is based on the widely accepted bound polaron theory for insulating ferromagnets. In our model, exchange mediating defects form magnetically active regions which behave like superparamagnetic clusters, however, unlike superparamagnetic systems the clusters are not precipitates or secondary phases, but magnetically active regions with size changing dynamically with temperature.