Effects of the bulk anisotropy on the surface magnetization

We study in this paper the magnetization singularity at the bulk critical temperature of a semi-infinite anisotropic Heisenberg model. In this analysis the surface is described by a Heisenberg model, while the bulk is given by an anisotropic Heisenberg model. Within the Greenʹs function formalism we find the slope of the surface magnetization at the bulk critical temperature. We show that this slope is discontinuous and the difference between the derivatives of the surface magnetization, just below and above the bulk critical temperature, can exhibit a minimum at a given value of the bulk anisotropy parameter.