Field-induced magnetic reorientation of the 2D Heisenberg ferromagnet with S = 1: the influence of an exchange anisotropy

The two-dimensional (2D) Heisenberg model with spin S = 1, with the exchange anisotropy plus a second-order uniaxial single-site anisotropy and an external transverse magnetic field is treated by the Tyablikov (Random Phase Approximation: RPA) decoupling of the exchange interaction term and the Anderson-Callen decoupling of the anisotropy term. The orientation of the magnetization is determined by the expectation values 〈Sα〉 (α = x, z) of the spin components from which the orientation angle θ is obtained as a function of the temperature and of the transverse magnetic field for various parameters of the exchange anisotropy in the (x,y)-plane. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)