Micromagnetism in mesoscopic epitaxial Fe dot arrays

The domain structures of epitaxial Fe (20 nm)/GaAs(100) circular dot arrays (diameters from 50 to 1 mu m) were studied with magnetic force microscopy. A transition from a single domain to a multidomain remanent state was obse rved upon reducing the dot diameter beneath 10 mu m in dot arrays with the separation twice the dot diameter. When the separation is reduced to half t he dot diameter, the single domain states were found to "collapse" into str ipe-like multidomain states due to local dipole coupling between dots. Micr omagnetic simulations further suggest that for ultrathin Fe dots of less th an about 2 nm thickness the diameter does not have a significant influence on the domain structures due to a dramatic reduction of the dipole energy. (C) 2000 American Institute of Physics. [S0021-8979(00)47608-5].