Micromagnetic modeling and analysis of linear array of square nanomagnets

We perform an analytical and a numerical micromagnetic study of the magnetostatic interactions and switching behavior in a linear array of square permalloy (Ni80Fe20) elements. The angular anisotropy in the magnetostatic energy of the array is expressed in terms of a shape anisotropy Ks arising from the square geometry of individual elements, and a “chain” anisotropy Kc due to inter-element dipolar interactions. An analytical model of Kc is introduced, which agrees closely with numerical results from the OOMMF micromagnetics package, in the limit of small element separation s. For s=5nm, the energy due to Kc far exceeds that of Ks by a factor of about 20. For larger s, the model is refined to account for the magnetostatic interaction between surface poles on neighboring elements. Based on the refined model, the analytical switching field Hsw is derived by assuming coherent rotation. It yields a close correspondence with OOMMF for s larger than s0=80nm, but significantly overestimates the numerical value for s