Switching characteristics and magnetization vortices of thin-film cobalt in nanometer-scale patterned arrays

The switching characteristics and magnetization vortices of 15 nm thick cobalt structures patterned to different widths of 100, 200, and 600 nm were investigated. The effects of linewidth and aspect ratio (length/width) were systematically studied using an alternating gradient magnetometer (AGM), an atomic force microscope/magnetic force microscope (MFM) and superconducting quantum interference device. The AGM and MFM show that trapped magnetization vortices appear in structures with low aspect ratios $\mathrm{(length/width)=1.5, 2},$ but not in structures with high aspect ratio $\mathrm{(length/width)=3,4}.$ It is found that the magnetization vortices of these patterned elements are strongly dependent on the width of the element with narrower linewidth more clearly showing the presence of magnetization vortices.