flatspin: A large-scale artificial spin ice simulator

We present flatspin, a novel simulator for systems of interacting mesoscopic spins on a lattice, also known as artificial spin ice (ASI). A generalization of the Stoner-Wohlfarth model is introduced, and combined with a well-defined switching protocol to capture realistic ASI dynamics using a point-dipole approximation. Temperature is modelled as an effective thermal field, based on the Arrhenius-Neel equation. Through GPU acceleration, flatspin can simulate the dynamics of millions of magnets within practical time frames, enabling exploration of large-scale emergent phenomena at unprecedented speeds. We demonstrate flatspin's versatility through the reproduction of a diverse set of established experimental results from literature. In particular, the field-driven magnetization reversal of "pinwheel" ASI is reproduced, for the first time, in a dipole model. Finally, we use flatspin to explore aspects of "square" ASI by introducing dilution defects and measuring the effect on the vertex population.