Artificially Structured Materials

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9732763 Chien This project deals with artificially structured materials, primarily quasi two-dimensional multilayers and one-dimensional nanowire arrays. Such materials exhibit novel properties due to their geometry, the interplay between constituent materials, and the degrees of freedom in their fabrication. The multilayer work will address key questions in ferromagnetic/antiferromagnetic (FM/AF)exchange coupling and magnetic/superconducting multilayers. Thus, the materials fabrication work will address the question of whether FM/AF coupling can be established between transition metal and rare earth moments. A further topic to be investigated in detail is the spatial variation of the FM/AF coupling as the individual layers in the multilayer arrays are traversed. The magnetic/superconducting multilayers employing ferromagnetic and antiferromagnetic constituents offer an excellent opportunity to investigate the pair-breaking mechanism arising in antiferromagnetic/superconducting planer interfaces, and superconducting ground state properties expressed in junction interfaces. Novel fabrication techniques have been developed to produce bismuth nanowire arrays that have been found to exhibit very large magnetoresistance. The origins of this and related electrical transport properties remain obscure and will be further investigated. The research involves graduate students in a range of fundamental projects that also have potential for major impact on technological areas such as information storage technology and the microelectronics industry. %%% This project deals with artificially structured materials such as quasi two-dimensional multilayers and one- dimensional nanowire arrays. Such materials exhibit novel properties due to their geometry, the interplay between constituent materials, and the degrees of freedom in their fabrication. These materials are of interest from fundamental viewpoints, but additionally have important technological applications in magnetic recording readheads, wide-range magnetic field sensing devises, and field emitters for flat panel displays. The magnetic interaction between multilayers leads to a phenomenon known as exchange biasing. This exchange biasing is at the heart of the new generation of high performance magnetic recording heads. Several key questions in the nature and mechanism of exchange biasing, and materials synthesis aspects of exchange biasing, will be explored. Nanowire arrays of bismuth will be investigated to understand origins of magnetoresistance in this semi- metallic material. The arrays show promise for applications for field sensing devices. The mechanism of the large magnetoresistance is poorly understood and the influence of fabrication methods on this transport property will be systematically investigated. The research involves graduate students in a range of fundamental projects that also have potential for major impact on technological areas such as information storage technology and the microelectronics industry. ***