We present a theory to study the temperature-dependent behavior of surfacestates in a ferromagnetic semi-infinite crystal. Our approach is based on thesingle-site approximation for the \emph{s-f} model. The effect of thesemi-infinite nature of the crystal is taken into account by a localizedperturbation method. Using the mean-field theory for the layer-dependentmagnetization, the local density of states and the electron-spin polarizationare investigated at different temperatures for ordinary and surface transitioncases. The results show that the surface magnetic properties may differstrongly from those in the bulk and the coupling constant of atoms plays adecisive role in the degree of spin polarization. In particular, for the casein which the exchange coupling constant on the surface and between atoms in thefirst and second layer is higher than the corresponding in the bulk, anenhancement of surface Curie temperature and hence the spin polarization can beobtained.
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