Simulated FMR to study in plane magnetic anisotropy of 3x3 array constituted by square base nickel nanopillars

A study about the magnetic anisotropy in plane of 3x3 arrays constituted by square base nickel nanopillars (NPs), with D = 30 nm width and L = 120 nm long, is presented. Variations in the effective anisotropy, due to the hard dipolar interactions, were provoked by modification in the interpillar distance, a-D = 5, 10, 20 and 50 nm. The data to study the anisotropy field, H _A, was collected from micromagnetic simulation performed by means of a ferromagnetic resonance (FMR) standard problem using the OOMMF package. The interpillar distance (face to face) was varied from the lower value, a-D = 5 nm where the dipolar interactions are very strong, to the maximum value, a-D = 50 nm were no longer significant are the dipole effects (to rescue the behavior of a single NP). Based on the isolated nanopillar symmetry, the initial proposed model for the collected data was the tetragonal anisotropy. The data showed a breaking of this symmetry for a-D ≤ 20 nm due to strong dipole interpillars interactions. Taking into account the array characteristics and the effects of local magnetization configuration at the corners of NPs, it was possible to propose a new model. The results are well described by the proposed model for all interpillar distance and, for a-D = 50 nm, the model coincides with the tetragonal symmetry compatible with the single pillar.