Fabrication of Nanowire-based Magnetic Structures for Magnetic Resonance Applications

Citation

Emery, Teresa Holly (2008) Fabrication of Nanowire-based Magnetic Structures for Magnetic Resonance Applications. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3XYZ-BW96. https://resolver.caltech.edu/CaltechETD:etd-06062008-115513

Abstract

The development and fabrication of novel magnetic nanowire devices is presented. These devices are used both to explore the fundamental physics of single domain particles, and to provide signal amplification and increased resolution in magnetic resonance imaging. Fabrication protocols for the creation of nickel nanowires were developed using both electron beam lithography and electroplating into nanoporous templates. The templates for electroplating were created by anodizing aluminum in either oxalic or sulfuric acids. The templates are 15 to 25 $mu$m thick and composed of highly ordered pores of 40 nm and 20 nm in diameter respectively. Nanowire samples formed by each protocol are characterized using an alternating gradient magnetometer to measure magnetic hysteresis loops. The magnets formed by electroplating were found to be much closer to ideal single domain magnets than those written via electron beam. Coercivities over to 1000 Oe were observed.

Individual cylindrical nanowires of 70 nm diameter were contacted using focused ion beam assisted platinum deposition. A contacted nanowire was tested in a cryostat to determine the temperature dependence of the magneto-resistive properties of the wire. Sections of plated nanowires still in the anodized aluminum template were examined for their reversible transverse susceptibility for applications in signal amplification in magnetic resonance imaging systems. A process of selectively plating into the aluminum templates to create shape magnets with interesting magnetic fields was developed for creating magnetic "lenses' with focal points above the plane of the substrate. Finally, an inductive stripe loop array was fabricated for use in stripe sensor tomography. These developments will enable future work on magnetic resonance imaging using a background of patterned templates for amplification.

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