Thickness dependent binary behavior of elongated single-domain cobalt nanostructures

We have studied the switching behavior of single-domain cobalt nanostructur es using a combination of magnetometry and magnetic force microscopy. The e longated 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 do uble-domain configuration becomes increasingly favorable as the thickness a pproaches 30 nm. The onset of this double-domain state agrees with previous ly reported numerical calculations. We also present a quantitative study of interparticle coupling in tightly packed arrays. The local dipolar field i ncreases the squareness of the hysteresis loop as the interparticle separat ion decreases below 400 nm. (C) 2000 American Institute of Physics. [S0021- 8979(00)04901-X].