Monte Carlo simulation study of the influence of defects on two-dimensional ferromagnetic order

We study the magnetic properties of two-dimensional (2D) ferromagnetic lattices with random disorders or ordered antidots through Monte Carlo simulations of the anisotropic Heisenberg model. We find that the Curie temperature (Tc) decreases linearly with the concentrations of the random vacancy of the magnetic moments (ρv) or the broken exchange interaction (ρb), and only the disorders with a concentration up to 30% can lead to a dropping of Tc by about half. The systems with a random broken exchange interaction have a much lower Tc than those with random vacancies at the same effective ρb, which suggests that the more randomness of the disorders in 2D ferromagnets induces a larger impact on Tc. When the magnetic anisotropy and exchange interaction become extremely small, Tc of the pristine lattice becomes much lower and the random disorders have a greater influence on Tc. The disorders also have an impact on the behavior of the correlation function. The correlation length decreases slower with temperature (T) just above Tc at a higher ρb, and its behavior is consistent with the disorder effect on the variation of heat capacity with T around Tc. For ordered antidot lattices, Tc can maintain a rather large value at a significantly low concentration of the remaining sites for systems with more than two chains of sites in one supercell.