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 seri es of cobalt and permalloy nanoscale dot arrays. The patterns were produced by e-beam lithography combined with e-beam deposition and lift-off techniq ues. To avoid pattern to pattern variations in growth-induced anisotropy an d or thickness, elliptical elements of varying aspect ratio were deposited simultaneously on a single substrate. All arrays were 1.0x2.5 mum tetragona l lattices and were fabricated with 300 Angstrom thickness of cobalt and wi th 200 and 300 Angstrom thickness of permalloy. From MOKE data we extract t he field at which the onset of switching occurs for each array. For each ma terial (viz. Co or permalloy), and thickness (200 or 300 Angstrom), the swi tching field versus aspect ratio can be interpreted by a single nucleation field. The dependence of the nucleation barrier on the material and its thi ckness is discussed. (C) 2000 American Institute of Physics. [S0003-6951(00 )00647-1].