Crystal field parameters at the (0001) surface of rare-earth metals: an ab initiostudy

Abstract

The modifications of the crystal field parametersAlm at the (0001) surface of the rare-earth metals Tb, Dy, Ho, Er and Tm due to thesurface-induced modifications of the charge density are investigated by the ab initio densityfunctional electron theory. For the three outermost atomic layers the values of the parametersA20,A40,A60 andA66 whichare nonzero for the hexagonal bulk are drastically different from the bulk values. The additional parametersA43 and A63 originating from the symmetry reduction at the surface are very large close to thesurface. Altogether, the results show that for a thermodynamic calculation ofthe spin structure at the surface a simple broken-bond model does not suffice.