Gd(0001):: A semi-infinite three-dimensional heisenberg ferromagnet with ordinary surface transition

By comparing the surface and, bulk magnetization of smooth, well-ordered Gd samples, we show that the surface has an ordinary transition, i.e., a common Curie temperature for surface and bulk;. A quantitative statistical analysis of the temperature dependent magnetization is presented. Critical exponents for both surface, beta (S) = 0.83 +/- 0.04, and bulk, beta (B) = 0.376 +/- 0.015, are consistent with the semi-infinite three-dimensional Heisenberg model with homogeneous exchange.