| The fabrication and characterization of ferromagnetic nanostructures have become increasingly important areas of research. Arrays of patterned magnetic nanostructures are a preferred choice for emerging storage technologies because of thermal stability, signal-to-noise ratio, and storage density. The switching field and switching mechanism(s) of nanoelements depend on complex interplay between magnetic anisotropy, and magnetostatic and exchange energies. As element sizes decrease to critical length scales such as the magnetic exchange length, the micromagnetic structure can consist of either single domain patterns or more complex configurations.; The effects of shape, size and distribution of patterned magnetic nanoelements on remanent states and magnetization reversal behavior have been investigated. Linear shapes such as ellipses and rectangles, circular shapes such as disks, rings, slotted rings and slotted-disks (pac-man), and complex shapes such as triangles, pentagons, hexagons and dumbbells have been examined. Elements with sizes ranging from 200 nm to 700 nm were patterned individually and in groups with different interelement distances to study magnetic interactions between neighboring elements. The 10- and 30-nm-thick polycrystalline Co nanoelements were prepared using electron-beam lithography, thin-film deposition and lift-off processes. Lorentz microscopy and off-axis electron holography were used to record the remanent states and switching behavior of the patterned ferromagnets.; In linear shapes, centered single-vortex (SV) and single domain states were observed for smaller sizes and smaller aspect ratios. Multiple vortices and domain walls were observed for larger sizes and higher aspect ratios. In circular shapes, centered SV states were observed in small-sized elements whereas double-vortex (DV) states were observed in larger elements. In more complex shapes, centered SV states were observed in small elements, whereas off-centered vortices and domain walls were observed in larger elements. Novel shapes such as double-pacman (DPM) and slotted elliptical structures were investigated: For DPM elements, flux-closure states were observed for most shapes and sizes, and the amount of flux-leakage outside the elements was observed to be minimal. For slotted elliptical structures, the relative occurrences of the two most frequently occurring SV and DV remanent states were highly dependent on the applied field direction for initial saturation and the shape geometry. |
