First Principles Calculations for Structural, Electronic, and Magnetic Properties of Gadolinium-Doped Alumina Clusters

Atomic structures and physical properties of Gd-doped
alumina clustersnamely,
GdAl2n–1O3n and Gd2Al2n–2O3n with n = 1–10have
been studied within the framework of spin-polarized density functional
theory and the projector augmented wave pseudopotential method. We
find that the atomic structures of the host clusters (Al2O3)n are not changed significantly
by the substitutional doping of a Gd atom on Al sites. Our results
show that in the size range of the clusters we studied, a Gd atom
prefers a maximum 4-fold-coordinated Al-site, except for n = 8, in which a 5-fold-coordinated Al site is favored. The substitution
of Al with Gd atom is energetically favorable. This is in contrast
to the substitutional doping of Gd in the bulk alumina corundum structure
that is endothermic. There is a net magnetic moment of 7 μB per Gd atom, which is mostly localized on the Gd atom. Further
substitution of an Al atom with Gd in GdAl2n–1O3n clusters results in
the lowest-energy configuration's being either ferromagnetic or antiferromagnetic,
the difference between the two magnetic states being very small. The
variation in the magnetic state is found to be associated with the
variation in the coordination number of Gd atoms and the sites of
the two Gd atoms. Our results suggest that Gd doping of nanoparticles
offers an interesting way to prepare Gd-doped ceramic materials.