Vertically aligned Fe arrays have been self-assembled on anodic aluminum oxide templates by evaporation. The rims of the pores, which act as obstacles to the stacking of atoms, prevent them from forming continuous films. By controlling the Fe nominal thicknesses (tau(n)) from 400 to 5 nm, the morphology is changed from continuous film to isolated arrays, leading to the change of the predominant magnetization reversal from domain wall motion to spin rotation. For samples with tau(n)<59 nm, isolated, rather than interconnected, morphology is formed. In this range, the coercivity shows a spectacular change for tau(n) = 47 nm, with an array diameter of about 52 nm, achieving a maximum of about 38 kA/m. The critical dimension of single-domain array is therefore determined. The magnetostatic and exchange interactions are reduced due to the thermal fluctuation, and the magnetization leaves from the in-plane direction to be randomly distributed in 3-D, for tau(n)<27 nm. (C) 2010 Elsevier B.V. All rights reserved.