Magnetization Reversal of Rectangular Particles: Closure States and Effect of Dipolar Coupling

We have investigated the magnetization configurations of ferromagnetic rectangular particles with lateral dimensions 1025 450 nm and two different thicknesses: 10 and 40 nm. For each thickness, we analyzed both an array consisting of isolated particles and a second one where the nanomagnets are put head-to-tail, with 85 nm interdot spacing, forming long chains of closely-spaced elements. Magneto- optical Kerr effect measurements and in-field magnetic force microscopy experiments were performed to achieve a deep comprehension of the magnetization reversal process. It is shown that inter-particle dipolar coupling substantially modifies the reversal mechanism in the case of the largest thickness, where it can delay or even suppress the occurrence of closure configurations of the magnetization (with one or more vortices), that are typical of isolated nanomagnets.