Magnetism of self-ordered and composite nanostructures

Nanostructured magnetic materials (NMM) have attracted much attention recently due to their unique structural and magnetic properties compared to continuous thin films or bulk materials. Our ability to fabricate artificial nanostructures makes it possible to test fundamental magnetism theories, and also enables us to produce materials with better properties and devices with ever smaller feature sizes.; Two examples of NMM studied in this thesis are self-ordered nanowire arrays and nanocomposite films. A traditional method to produce periodic arrays of nanoscale magnetic dots and wires is nano-lithography, which is comparatively cumbersome and not suitable for large-area production. Alternatively templates made by various methods are used to produce nano dots or wires by electrodeposition or lithographic patterning. In this work, porous anodic alumina, created by anodization of aluminum in acidic solutions, is used as templates for electrodeposition of ferromagnetic metals. Particularly interesting problems of the magnetism of nanowires are the magnetic hysteresis of the wires and the time-dependent magnetization reversal. It is well-known that simple reversal mechanisms, such as coherent rotation and curling, are unable to account for the observed hysteretic behavior. Systematic measurements of time- and temperature-dependent magnetic properties for ferromagnetic nanowire arrays as a function of wire dimensions reveal a novel magnetization reversal mechanism, which is localized in nature.; Tetragonal FePt and CoPt based nanocomposite films with exchange decoupled high anisotropy grains embedded in a nonmagnetic matrix are promising candidates for future high-density recording media. (001) textured FePt, CoPt and their nanocomposite films have been produced non-epitaxially on ordinary glass or Si substrates. The orientation mechanism has been studied systematically. The nonmagnetic matrix affects the local atomic environments of magnetic grains. The effects of the matrix material on the structural and fundamental magnetic properties are investigated both experimentally and theoretically. Elemental doping has been carried out to tailor the properties for recording applications.