Cross-over from coherent rotation to inhomogeneous reversal mode in interacting ferromagnetic nanowires

We have investigated the magnetization reversal mechanism and the effects of magnetostatic interaction in arrays of lithographically defined Permalloy nanowires with a fixed width of 185 nm, spacing of 35 nm and film thicknesses from 10 to 120 nm. The magnetization reversal has been investigated with vectorial Magneto-Optical Kerr Effect magnetometry. The vectorial hysteresis loops (in-plane magnetization components parallel and perpendicular to the applied field) recorded with the external field applied perpendicular to the length of the wires (hard magnetization direction), show a transition from coherent rotation to inhomogeneous reversal mode for wires' thickness above 80 nm. The effects of dipolar interactions are evidenced by the variation of the saturation field in the hard-axis hysteresis loops as a function of wires thickness. In detail, the analysis of the saturation field vs. wires thickness shows that the dipolar interactions start to play a role for wires thickness >= 20 nm. (c) 2007 Elsevier B.V. All rights reserved.