Transition from a single-domain to a multidomain state in mesoscopic ferromagnetic Co structures

We have performed magnetic force microscopy measurements on isolated 35 nm thick rectangular Co structures. The structures have a length L ranging bet ween 0.25 and 10 mum and a width W ranging between 0.25 and 5.5 mum, coveri ng aspect ratios m = L/W between 1 and 40. This enables us to map the trans ition from a magnetic single-domain state towards a magnetic multidomain st ate when increasing the size of the structures. This transition depends on the size as well as the aspect ratio of the structures. Our results can be interpreted in terms of the theoretical model developed by A. Aharoni [J. A ppl. Phys. 63, 5879 (1988)]. (C) 2001 American Institute of Physics.