Field dependence of the susceptibility maximum in the anisotropic Heisenberg ferromagnet

The location and height of the susceptibility maximum for anisotropic one and two-dimensional spin S=12 Heisenberg models are investigated by using the Green's function treatment within the random phase approximation. The results are fitted to the power law behaviors, Tmχ-T0=ahγ and χ(Tmχ)=bh-β, in the high field. And the exponents γ,β are found to be dependent of the anisotropy. Our results do not support the 23 power laws which are obtained from the mean-field Landau's theory. For the isotropic and Ising cases, the exponents γ,β which are in agreement with the results by other theoretic techniques.