Porous aluminum oxide templates for nanometer-sized cobalt arrays

Nanometer-sized Co arrays consisting of 200 nm or 20 nm diameter cylindrical islands, occupying a fractional surface area of 50 to 65%, have been synthesized by electrodeposition through the pores of suitable Al oxide templates. An increase in coercivity for 20 nm compared to 200 nm diameter Co island arrays is explained in terms of a transition to a single domain state. In this size range, demagnetizing fields have a major role in determining the magnetic response of the arrays, which show high saturation fields and a coercivity which is lower than predicted by curling or uniform rotation models. A high effective anisotropy is important in obtaining relatively high values of coercivity (up to 1700Oe) in highly packed arrays.