Magnetostatic interactions and magnetization reversal in ferromagnetic wires

We have investigated the effect of magnetostatic interactions on the magnetization reversal behavior of ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ flat wire arrays using magnetoresistance (MR) measurements. The wires are fabricated from films of thickness 500 Å. As the separation s of a wire array of fixed width w=2 μm is increased, a crossover from the behavior characteristic of an interacting wire array to that of a single isolated wire is identified for $s/w\sim 1$. For the interacting limit, $s/w<~1$, a marked reduction in the coercive field occurs as the spacing of wires of fixed width are decreased. The shape of the MR response to fields applied along the hard axis is also found to be strongly dependent on the interwire separation. We attribute this behavior to the effect of interwire dipolar interactions. MR measurements were also made as a function of the orientation of the applied field relative to the axis of the wire, in order to investigate how the shape anisotropy affects the magnetization reversal process. In μm-size wires we find that “one-jump” switching of the magnetization can occur according to the orientation of the wires with respect to the applied field.