  We have studied the temperature and magnetic field dependence of the total
magnetic moment of large-area permalloy artificial square spin ice arrays. The
temperature dependence and hysteresis behavior are consistent with the coherent
magnetization reversal expected in the Stoner-Wohlfarth model, with clear
deviations due to inter-island interactions at small lattice spacing. Through
micromagnetic simulations, we explore this behavior and demonstrate that the
deviations result from increasingly complex magnetization reversal at small
lattice spacing, induced by inter-island interactions, and depending critically
on details of the island shapes. These results establish new means to tune the
physical properties of artificial spin ice structures and other interacting
nanomagnet systems, such as patterned magnetic media.

Mesoscale and Nanoscale Physics