Quantum Monte Carlo study of the two-dimensional ferromagnet

We present Quantum Monte Carlo calculations that probe the paramagnet-ferromagnet phase transition in a two-dimensional Stoner Hamiltonian. With a screened Coulomb interaction we observe a first order ferromagnetic transition for short screening lengths, and a second order transition with a longer screening length, accompanied by a rising critical interaction strength. Finally, we discuss the consequences of our results for an ultracold atomic gas with finite ranged interactions.