Comparing frustrated and unfrustrated clusters of single-domain ferromagnetic islands

We have studied the magnetic-moment configurations of different geometry clusters of single-domain nanoscale ferromagnetic islands. The clusters consisted of four islands arranged in geometries taken from the square lattice of artificial spin ice. The magnetic-moment configurations were imaged by magnetic force microscopy after effectively annealing through ac demagnetization. We then compared the results for cluster geometries with and without frustration of the magnetostatic interactions between the island moments. We found that nonfrustrated clusters achieve their lowest energy states more readily than do frustrated clusters. This behavior suggests the presence of a kinetic barrier associated with frustration of the magnetostatic interactions.