  Frustrated arrays of interacting single-domain nanomagnets provide important
model systems for statistical mechanics, because they map closely onto
well-studied vertex models and are amenable to direct imaging and custom
engineering. Although these systems are manifestly athermal, we demonstrate
that the statistical properties of both hexagonal and square lattices can be
described by an effective temperature based on the magnetostatic energy of the
arrays. This temperature has predictive power for the moment configurations and
is intimately related to how the moments are driven by an oscillating external
field.
