Micromagnetic modeling and analysis of linear array of square nanomagnets

Abstract 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 K s arising from the square geometry of individual elements, and a “chain” anisotropy K c due to inter-element dipolar interactions. An analytical model of K c is introduced, which agrees closely with numerical results from the OOMMF micromagnetics package, in the limit of small element separation s. For s = 5 nm , the energy due to K c far exceeds that of K s 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 H sw is derived by assuming coherent rotation. It yields a close correspondence with OOMMF for s larger than s 0 = 80 nm , but significantly overestimates the numerical value for s s 0 . This is due to the onset of sequential reversal at s = s 0 brought about by strong dipolar coupling between elements. The critical nucleation and the propagation fields associated with sequential reversal are also investigated as a function of s .