Fabrication, characterization, manipulation and application of magnetic nanostructures

Nanostructured materials have not only abundant new physics but also application importance. Nanosciences include developing new techniques and exploring new phenomena. This dissertation presents the fabrication and property investigation of magnetic nanowires and exchange coupled NiFe/CoO nanostructured networks. Functionalization and potential biomedical applications of multicomponent nanowires are discussed.; Using nuclear track etching, nanopores with controlled areal density (1−1011/cm2) and size (diameter > 10nm) are fabricated in polycarbonate membranes and mica single crystal wafers. Pore morphology depends strongly on the etching properties of the matrix. In contrast to the cylindrical pores in polycarbonate, etched nanopores in single crystalline mica membranes maintain diamond shape cross-sections, as a replica of the oxygen terminated planes of the unit cell. Compared to conventional nanoporous polymer membraness, mica template provides better thermal stability, chemical stability, mechanical rigidity and atomically smooth surfaces.; Different materials have been electrodeposited into the pores to form nanowires. Magnetic properties of the electrodeposited Ni nanowires exhibit strong size dependence. Coercivity and remnant magnetization increase with decreasing nanowire diameter. High temperature measurements on the Ni nanowires in mica show finite size effects in the quasi-one dimensional structures. Curie temperature shifts to lower temperature with decreasing wire diameter and follows the finite size scaling law. Due to the diamond shape wire cross-section, in-plane magnetic anisotropy based on two mutually perpendicular anisotropic axes has been observed. We also studied the magnetization reversal process when the external field rotated away from wire axis. In the 120nm Ni nanowires, transition from switching based on curling to coherent rotation has been observed when the angle between the field and wire axis is about 80°.; Single nanowire manipulation based on removing the matrix to expose nanowires has been explored. Nanowire suspensions are prepared and magnetic response of the Ni nanowire in suspensions has been studied. Single nanowire has been contacted by lithography, electric trapping and magnetic trapping. Single wire transport measurements have been done on Pt nanowires by optical lithography.; With the capability of making high aspect ratio nanowires with different composition by electrodeposition, the use of multi-component magnetic nanowires as a biomedical “delivery vehicle” is discussed.; Non-uniform FM/AFM exchange coupled network structures have been fabricated by sputtering CoO and NiFe onto nanoporous alumna membranes. With the average ligament of 120nm long and 40nm wide, the nanosturctured bilayer shows great H_E and H_c enhancement compared to uniform film. The change can be attributed to domain confinement and pinning effect of the walls due to microstructures. This provides another degree of freedom to control the coercivity and exchange bias of materials by changing the geometry and size of the bilayers.