Magneto-optic Kerr effect investigation of cobalt and permalloy nanoscale dot arrays: Shape effects on magnetization reversal

Using the magneto-optic Kerr effect (MOKE) and magnetic force microscopy we have investigated the shape dependence of magnetization reversal in a series of cobalt and permalloy nanoscale dot arrays. The patterns were produced by e-beam lithography combined with e-beam deposition and lift-off techniques. To avoid pattern to pattern variations in growth-induced anisotropy and or thickness, elliptical elements of varying aspect ratio were deposited simultaneously on a single substrate. All arrays were 1.0×2.5 μm tetragonal lattices and were fabricated with 300 Å thickness of cobalt and with 200 and 300 Å thickness of permalloy. From MOKE data we extract the field at which the onset of switching occurs for each array. For each material (viz. Co or permalloy), and thickness (200 or 300 Å), the switching field versus aspect ratio can be interpreted by a single nucleation field. The dependence of the nucleation barrier on the material and its thickness is discussed.