Magnetic nanostructures have been subject of intense research as a result of their unique magnetic properties such as superparamagnetism, enhanced magnetic moment, and high magnetic density storage due to shape anisotropy. A highly reproducible and affordable method to fabricate cobalt nanostructures on silicon substrates was devised in this thesis using nanosphere lithography. The surface morphology and magnetic properties of the nanopatterned cobalt thin film were characterized using an optical microscope, scanning electron microscope, atomic force microscope, and a magneto optical Kerr effect (MOKE) magnetometer. Modification to the surface of cobalt thin film was found to extensively alter its magnetic coercivity. Continuous cobalt thin film at 10 nm thick has a coercivity of 102±2 Oe, whereas nanostructured cobalt thin films at the same thickness have a coercivity of 167±16 Oe. The magnetic coercivity increases by 65±18 Oe for an array of close packed cobalt nanostructures using nanosphere templates with diameters ranging from 203 nm to 600 nm. The cobalt nanostructured sample using a 930 nm diameter nanosphere template has a coercivity comparable to a continuous cobalt thin film at 108±7 Oe. In addition, these nanostructures exhibit unusual magnetic properties such as multistep behavior and pinching/crossing-over of the magnetization curves with regards to the MOKE signal. These features become more prominent as the diameter of the nanosphere template decreases.
|Commitee:||Bill, Andreas, Gredig, Thomas|
|School:||California State University, Long Beach|
|Department:||Physics and Astronomy|
|School Location:||United States -- California|
|Source:||MAI 56/03M(E), Masters Abstracts International|
|Subjects:||Nanoscience, Physics, Condensed matter physics|
|Keywords:||Coercivity, Ferromagnetic, Magneto optical, Nanosphere lithography, Nanostructure, Pinching crossing over multistep|
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