We investigated electronic structure of hexagonal multiferroic YMnO3 using the polarization dependent x-ray absorption spectroscopy (XAS) at O K and Mn L(2,3) edges. The spectra exhibit strong polarization dependence at both edges, reflecting anisotropic Mn 3d orbital occupation. Moreover, the O K edge spectra show that Y 4d states are strongly hybridized with O 2p ones, resulting in large anomalies in Born effective charges on off-centering Y and O ions. These results manifest that the Y d(0)-ness with rehybridization is the driving force for the ferroelectricity, and suggest a new approach to understand the multiferroicity in the hexagonal manganites.

Articles you may be interested inEnhanced indirect ferromagnetic p-d exchange coupling of Mn in oxygen rich ZnO:Mn nanoparticles synthesized by wet chemical method J. Appl. Phys. 111, 033503 (2012); 10.1063/1.3679129Room temperature ferromagnetic and ultraviolet optical properties of Co-doped ZnO nanocluster films Zinc oxide bicrystal nanobelts were fabricated via a vapor phase transport of a powder mixture of Zn, BiI 3 , and MnCl 2 ·H 2 O at temperatures as low as 300°C. The bicrystal nanobelts, growing along the ͓011 − 3͔ direction, have the widths of 40-150 nm and lengths of tens of microns. The energy dispersive x-ray spectroscopy result verifies that the bicrystal nanobelts contain higher concentration of both Bi and Mn along the grain boundary. The investigation of the growth mechanism proposes that MnBi may induce the formation of bicrystal nanobelts. Photoluminescence spectra show that the ultraviolet emission of the bicrystal nanobelts has a blueshift of 18 meV as compared to Bi-ZnO nanowires at 10 K. The bicrystal nanobelts also exhibit ferromagnetism at room temperature.

ZnO hierarchical nanostructures containing Bi2O3 have been prepared using Zn–Bi droplets. Transmission electron microscopy analyses indicate that some β-Bi2O3 nanoparticles (2–3 nm) are embedded inside hexagonal ZnO hierarchical nanostructures. It turns out that the morphologies are sensitive to temperature. The photoluminescence spectrum at 10 K shows a sharp free exciton line at 3.374 eV, which implies that the nanostructures are of high optical quality. The blue shift of green emission centred at 492 nm (2.515 eV), which can be attributed to the emission from Bi3+, is also observed.

Starting from a mixture of Zn and BiI3, we grew nanowires and nanoplates on an oxidized Si substrate at relatively low temperatures of 250 and 300 degrees C, respectively. The ZnO nanowires had diameters of approximately 40 nm and grew along the [110] direction rather than the conventional [0001] direction. The nanoplates had thicknesses of approximately 40 nm and lateral dimensions of 3-4 microm. The growth of both the nanowires and nanoplates is dominated by the synergy of vapor-liquid-solid (VLS) and direction conducting. Analysis of photoluminescence spectra suggested that the nanoplates contain more oxygen vacancies and have higher surface-to-volume ratios than the nanowires. The present results clearly demonstrate that the shapes of ZnO nanostructures formed by using BiI3 can be controlled by varying the temperature in the range 250-300 degrees C.