2D ferromagnetic models with symmetry-breaking interactions: self-consistent harmonic approximation

Abstract

The 2D classical planar rotator, XY and Heisenberg ferromagnetic models with uniaxial in-plane anisotropy are investigated using self-consistent harmonic approximation. We found that for sufficiently large anisotropy there is implemented the phase transition from ferromagnetic phase into paramagnetic one. We also determine the range of anisotropy values for which the XY and planar rotator models undergo phase transition in temperature from the state with long-range magnetic order into Berezinskii–Kosterlitz–Thouless phase with topological order. The same calculations are carried out for the models with magnetoelastic coupling.