The recent discovery of ferromagnetism above room temperature in low-temperature-processed MnO(2)-ZnO has generated significant interest. Using suitably designed bulk and thin-film studies, we demonstrate that the ferromagnetism in this system originates in a metastable phase rather than by carrier-induced interaction between separated Mn atoms in ZnO. The ferromagnetism persists up to approximately 980 K, and further heating transforms the metastable phase and kills the ferromagnetism. By studying the interface diffusion and reaction between thin-film bilayers of Mn and Zn oxides, we show that a uniform solution of Mn in ZnO does not form under low-temperature processing. Instead, a metastable ferromagnetic phase develops by Zn diffusion into the Mn oxide. Direct low-temperature film growth of Zn-incorporated Mn oxide by pulsed laser deposition shows ferromagnetism at low Zn concentration for an optimum oxygen growth pressure. Our results strongly suggest that the observed ferromagnetic phase is oxygen-vacancy-stabilized Mn(2-x)Zn(x)O(3-delta.).

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We have made epitaxial and polycrystalline thin films of multiferroic BiFeO 3 on different substrates ͓͑001͒ and ͑111͒ SrTiO 3 , ͑001͒ and ͑111͒ LaAlO 3 , ͑001͒ MgO, and ͑0001͒ sapphire͔ by pulsed-laser deposition. We investigated the second harmonic generation ͑SHG͒ in these films and find that the SHG was smallest in epitaxially grown films on ͑001͒ SrTiO 3 and largest in epitaxial films grown on ͑111͒ SrTiO 3 and ͑111͒ LaAlO 3. We discuss these results in terms of the crystal structure as well as the film microstructure.

A nondestructive method for the high-throughput screening of novel bond coat materials has been developed. By using a suite of characterization techniques, including Raman spectroscopy, fluorescence spectroscopy, and X-ray diffraction, a rapid determination of thermally grown oxide phases and their protective capability over a continuous composition spread sample can be obtained. The methodology is validated with the Ni-Al system. The procedure developed in this work results in the rapid identification of bond coat composition regions in which the preferred thermally grown oxide, α-Al2O3, is nucleated thus significantly reducing the amount of phase space that needs to be explored in subsequent studies.