POROUS ALUMINUM-OXIDE TEMPLATES FOR NANOMETER-SIZED COBALT ARRAYS

Nanometer-sized Co arrays consisting of 200 nm or 20 nm diameter cylin drical islands, occupying a fractional surface area of 50 to 65%, have been synthesized by electrodeposition through the pores of suitable A l 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 pred icted by curling or uniform rotation models. A high effective anisotro py is important in obtaining relatively high values of coercivity (up to 1700Oe) in highly packed arrays.