The magnetization in an infinite two-dimensional hexagonal array of small magnetic single-domain nanoparticles is studied by theoretical calculations. Various hysteresis loops and analytical expressions of coercivity and saturation field of the system with different particle sizes and array densities are obtained under the assumption of magnetization reversal mechanisms based on the competition between the dipolar interaction energy and the shape anisotropy energy with an external magnetic field perpendicular to the array plane. The hysteresis loop varies from a rectangle to a nonhysteresis straight line through a set of complicated loops composed of two types, which is in accordance with the magnetization reversal process varying from an independent coherent rotation to an “antisymmetric-ferromagnetic chain” mechanism. Our results can give a reasonable reference to the application of perpendicular magnetic recording media.

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