Browsing by Author "Du, Y"

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    The magnetic structure of an epitaxial BiMn0.5Fe0.5O3 thin film on SrTiO3 (001) studied with neutron diffraction
    (American Institute of Physics, 2012-10-22) Cortie, DL; Stampfl, APJ; Klose, F; Du, Y; Wang, XL; Zhao, HY; Kimura, H; Cheng, ZX
    High-angle neutron diffraction was used to directly reveal the atomic-scale magnetic structure of a single-crystalline BiMn0.5Fe0.5O3 thin film deposited on a SrTiO3 (001) substrate. The BiMn0.5Fe0.5O3 phase exhibits distinctive magnetic properties that differentiate it from both parent compounds: BiFeO3 and BiMnO3. A transition to long-range G-type antiferromagnetism was observed below 120K with a (1/2 1/2 1/2) propagation vector. A weak ferromagnetic behavior was measured at low temperature by superconducting quantum interference device (SQUID) magnetometry. There is no indication of the spin cycloid, known for BiFeO3, in the BiMn0.5Fe0.5O3 thin film. The neutron diffraction suggests a random distribution of Mn and Fe over perovskite B sites. © 2012, American Institute of Physics.
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    Suppression of the spin spiral in an antiferromagnetic BiFe 0.5 Mn 0.5 O3 thin film and powder
    (Australian Institute of Physics, 2012-02-02) Cortie, DL; Du, Y; Cheng, ZX; Klose, F; Wang, XL
    Since the advent of the spintronics paradigm [1], there has been a resurgence of interest in materials that simultaneously possess magnetic and ferroelectric ordering [2]. Such materials provide the realistic prospect of manipulating magnet elements using electric fields at room temperature. While electric field control has recently been demonstrated using the interfacial coupling between a multiferroic oxide and a metallic thin film [3], there is still a search to find a suitable single phase ferromagnetic multiferroic [4,5]. Previous work reported that a metastable phase of BiMnO3 was ferromagnetic with a Curie temperature of 99K [5] whereas BiFeO3 . is a canted anti-ferromagnetic below 640K with ferroelectric order [2]. We explored the effect on magnetic structure of including high percentages of Mn into a BiFeO3 host in a La0.2BiFe 0.5 Mn 0.5 O3 compound. Neutron diffraction was performed on an epitaxial nanoscale film using the instrumentation at ANSTO to obtain the magnetic structure at low temperature, and the results were compared with powders and magnetometry data. The neutron data for the film and powders both indicate a single magnetic transition to a highly collinear G-type antiferromagnetic order where the incommensurate spin spiral present for BiFeO3 appears to be suppressed by the addition of Mn . The Neél temperature is shifted to 225 K. The c/a ratio of the unit cell is found to differ between thin film and the powder suggesting that the epitaxial lattice matching to the SrTiO3 substrate strains the film in the ab plane but preserves the overall unit cell volume leading to a lattice expansion in the c direction and a further reduction in Neel temperature to 130 K. The magnetic properties of the film and powder appear to be dramatically different from the properties of nanoparticles reported for the same compound which showed multiple magnetic transitions to higher temperatures [4].
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    Synthesis and thermoelectric properties of single crystalline and polycrystalline Ba8Ga16Ge30
    (Elsevier, 2010-02-18) Wang, HF; Cai, KF; Li, H; Yu, DH; Wang, XC; Zhou, CW; Li, XL; Wang, YY; An, BJ; Du, Y
    Large Ba8Ga16Ge30 single crystals were synthesized by a Ga-flux method. The single crystals were characterized by X-ray diffraction and energy-dispersive X-ray spectroscopy. The cubic structure of Ba filled type-I germanium clathrates with lattice parameter of 10.767 Å has been confirmed. The Ba8Ga16Ge30 polycrystalline sample was prepared by melting the synthesized single crystals. Thermoelectric properties of the single crystalline and polycrystalline Ba8Ga16Ge30 samples were measured from room temperature to 773 K. The single crystalline sample shows p-type conduction, while the polycrystalline sample exhibits n-type conduction and typical heavily doped semiconducting behavior. At room temperature, the electrical conductivity of the polycrystalline sample is much higher than that of the single crystalline sample, whereas the absolute value of Seebeck coefficient of the single crystalline sample is higher than that of the polycrystalline sample. The maximum power factor for the single crystalline and polycrystalline samples reaches ~17 μW cm−1 K−2 at 773 K and ~10 μW cm−1 K−2 at 500 K, respectively. © 2010, Elsevier Ltd.