Nonuniversal critical behavior of magnetic dipoles on a square lattice

摘要: We study the thermal transition between paramagnetic and antiferromagnetic phases of interacting magnetic dipoles on square lattices in two dimensions. By Monte Carlo simulations, we find strong long-range order low temperature phase a critical behavior that is, as fourfold anisotropic XY model, nonuniversal, single-site quadrupolar anisotropy ${h}_{4}$ is relevant variable. However, indices differ markedly from ones for model. They vary Ising type, within errors, ${h}_{4}=0$, to ${h}_{4}\ensuremath{\rightarrow}\ensuremath{\infty}$ limit nearly abrupt first-order transition.