Browsing by Author "Huang, YJ"

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    Magnetic and electronic co states in the layered cobaltate GdBaCo2O5.5-x
    (American Physical Society, 2008-08) García-Fernández, M; Scagnoli, V; Staub, U; Mulders, AM; Janousch, M; Bodenthin, Y; Meister, D; Patterson, BD; Mirone, A; Tanaka, Y; Nakamura, T; Grenier, S; Huang, YJ; Conder, K
    We have performed nonresonant x-ray diffraction, resonant soft and hard x-ray magnetic diffraction, soft x-ray absorption, and x-ray magnetic circular dichroism measurements to clarify the electronic and magnetic high-spin (HS) state at the states of the Co3+, ions in GdBaCo2O5.5. Our data are consistent with a Co-Py(3+) pyramidal sites and a Co-Oc(3+), low-spin (LS) state at the octahedral sites. The structural distortion with a doubling of the a axis (2a(p)X2a(p)X2a(p) cell) shows alternating elongations and contractions of the pyramids, and indicates that the metal-insulator transition is associated with orbital order in the t(2g) orbitals of the Co-Py(3+) HS state. This distortion corresponds to an alternating ordering of xz and yz orbitals along the a and c axes for the Co-Py(3+). The orbital ordering and pyramidal distortion lead to deformation of the octahedra but the Co-Oc(3+) LS state does not allow an orbital order to occur for the Co-Oc(3+), ions. The soft x-ray magnetic diffraction results indicate that the magnetic moments are aligned in the ab plane but are not parallel to the crystallographic a or b axes. The orbital order and the doubling of the magnetic unit cell along the c axis support a noncollinear magnetic structure. The x-ray magnetic circular dichroism data indicate that there is a large orbital magnetic contribution to the total ordered Co moment. © 2008, American Physical Society
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    Zr-Cu-Ni-Al bulk metallic glasses with superhigh glass-forming ability.
    (Elsevier, 2009-02) Sun, YJ; Qu, DD; Huang, YJ; Liss, KD; Wei, XS; Xing, DW; Shen, J
    Zr-Cu-Ni-Al quaternary amorphous alloy compositions with varying glass-forming ability are developed by an efficient method of proportional mixing of binary eutectics. The critical diameter of the glassy sample is improved from 6 mm for Zr53Cu18.7Ni12Al16.3 to 14 mm for Zr50.7Cu28Ni9Al12.3 by straightforwardly adjusting the eutectic unit's coefficients. The drastic improvement in GFA is attributed to balancing, the chemical affinities of the Zr, Cu, Ni and Al components in the melt prior to solidification which makes the precipitation of competing crystalline phases more difficult. As the glass-forming ability increases, the concentration Of Cu ill the alloys exhibits a same trend. Based on synchrotron radiation high-energy X-ray diffraction analysis and Miracle's structural model, it is envisioned that the substitution of additional Cu Morris for Zr atoms in the investigated alloys stabilizes the efficient cluster packing structure of the amorphous alloys, leading to the pronounced increase ill their glass-forming ability. © 2008, Elsevier Ltd.