Magnetic anisotropy and domain patterns in electrodeposited cobalt nanowires

The magnetic anisotropy and domain structure of electrodeposited cylindrica l Co nanowires with length of 10 or 20 mum and diameters ranging from 30 to 450 nm are studied by means of magnetization and magnetic torque measureme nts, as well as magnetic force microscopy. Experimental results reveal that crystal anisotropy either concurs with shape anisotropy in maintaining the Co magnetization aligned along the wire or favours an orientation of the m agnetization perpendicular to the wire, hence competing with shape anisotro py, depending on whether the diameter of the wires is smaller or larger tha n a critical diameter of 50 nm. This change of crystal anisotropy, originat ing in changes in the crystallographic structure of Co, is naturally found to strongly modify the zero (or small) field magnetic domain structure in t he nanowires. Except for nanowires with parallel-to-wire crystal anisotropy (very small diameters) where single-domain behaviour may occur, the format ion of magnetic domains is required to explain the experimental observation s. The geometrical restriction imposed on the magnetization by the small la teral size of the wires proves to play an important role in the domain stru ctures formed.