Magnetic coupling of stripe domains in FePt/Ni80Fe20 bilayers

Abstract

Equiatomic FePt in the A1 soft magnetic phase and Ni80Fe20 (permalloy) thin films form a stripe-like magnetic domain structure above a critical thickness. This critical thickness is considerably different in the two alloys and allows us to study the influence of the magnetic coupling in the domain configuration in bilayers. Using dc magnetron sputtering techniques, we fabricated two different sets of FePt/Ni80Fe20 bilayers, keeping one thickness fixed and varying the other, and investigated the dc magnetic properties and the magnetic domain configuration of the structure. In all cases, magnetization reversal occurred at a single coercive field, indicating a relatively strong magnetic exchange coupling between both layers. The observed stripe period was also consistent with a model of spring magnet-like behavior. However, for certain values of FePt and permalloy thickness a complex nonparallel double stripe structure was found, which may be attributed to the influence of the dipolar stray field of the thicker layer on the stripe structure of the thinner film.