  We report here the results of micromagnetic simulations of square artificial
spin ice (ASI) systems with defects. The defects are introduced by misaligning
of a nanomagnet at the vertex. In these defective systems, we are able to
stabilize emergent monopole-like state by applying a small external field. We
observe a systematic change of dipolar energies of the systems with varying
misalignment angle. The fields at which the emergent monopoles are created vary
linearly with the dipolar energies of the systems. Our results clearly show
that the magnetization reversal of the ASI systems is intricately related to
the interplay of defects and dipolar interactions.
