Thickness dependent binary behavior of elongated single-domain cobalt nanostructures

We have studied the switching behavior of single-domain cobalt nanostructures using a combination of magnetometry and magnetic force microscopy. The elongated nanostructures are 80×140 nm wide, and range in thickness from 14 to 30 nm. Structures thinner than 20 nm form a single-domain binary system featuring two preferred orientations of the magnetization. An additional double-domain configuration becomes increasingly favorable as the thickness approaches 30 nm. The onset of this double-domain state agrees with previously reported numerical calculations. We also present a quantitative study of interparticle coupling in tightly packed arrays. The local dipolar field increases the squareness of the hysteresis loop as the interparticle separation decreases below 400 nm.