  We have performed a detailed study of thermal annealing of the moment
configuration in artificial spin ice. Permalloy (Ni$_{80}$Fe$_{20}$) artificial
spin ice samples were examined in the prototypical square ice geometry,
studying annealing as a function of island thickness, island shape, and
annealing temperature and duration. We also measured the Curie temperature as a
function of film thickness, finding that thickness has a strong effect on the
Curie temperature in regimes of relevance to many studies of the dynamics of
artificial spin ice systems. Increasing the interaction energy between island
moments and reducing the energy barrier to flipping the island moments allows
the system to more closely approach the collective low energy state of the
moments upon annealing, suggesting new channels for understanding the
thermalization processes in these important model systems.
