Dipolar magnetic interactions in 3 x 3 arrays of rectangular Ni nanopillars

A study about magnetic behavior of 3x3 arrays, constituted by Ni squared pillars (SPs), is presented. Micro magnetic simulations using the OOMMF package reveal hysteresis loops that depend on the inter-pillar distance, d. Solid SPs with high L = 120 nm, lateral dimensions D (30 nm and 60 nm) and face to face distance d (20 nm and 30 nm) were used. Hollow pillars with rectangular cavity a (12 nm and 24 nm) were also placed at d = 20 and 30 nm. For hollow pillars, the angular dependence of coercivity was slightly different than that for the solid pillars. The lateral dimension (D) was the most relevant geometric parameter acting over magnetic behaviors. The reversal of magnetic moments occurs through magnetization jumps in the hysteresis curves. These jumps are very sensitive to the inter-pillar distance in the array. The maps of moments, at the remanence state, reveal that there are vortexes at the pillars extremes. These maps also reveal that the effect of the internal and external surfaces, in hollow pillars, interact enough to modify the vector configuration. The effects of lateral dimension, D are stronger manifested in hollow pillars, because the distance between the internal and external surfaces changes with a and D. The study presents itself with relevant results, significant to understand the behavior of magnetic objects with a square cross section.