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SEM images of nickel dot arrays fabricated by x-ray interference lithography: (a) , , , (b) , , , and (c) high resolution image showing edge irregularities for , , . The orientation of the applied field, , for MOKE measurements is indicated by the double headed arrow.
(a) MOKE hysteresis loops for nickel dot arrays with nm, and various dot diameters and separations. The shaded area highlights the region between 40 and where the transition from double to single switching occurs. Typical hysteresis loops with schematic diagrams showing (b) double switching via the vortex state, where and are the vortex nucleation and annihilation fields, respectively, and (c) single switching of collective spins.
Snap shot of a micromagnetic simulation showing flux closure through a dot array resulting in single switching in all but the dot farthest to the right. Parameters employed: , , simulation cell , , and . The magnetic spins were saturated with a field, H, in the positive direction which was then reduced to zero. The inset shows the vortex state which forms in an isolated dot.
PEEM image showing bands of contrast in a nickel dot array with , , and . The direction of the demagnetizing field, , which is the same as the magnetization sensitivity direction, is indicated by the double-headed arrow. The contour plot is the Fourier transform of the image, confirming the directionality. The expanded section of the image is overlayed with a schematic of the dot array for comparison, showing that the bands are about two dots wide.
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