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 80x140 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. (C) 2000 American Institute of Physics. [S0021- 8979(00)04901-X].