  In this contribution we present some recent results about neutron halos in
deformed nuclei. A deformed relativistic Hartree-Bogoliubov theory in continuum
has been developed and the halo phenomenon in deformed weakly bound nuclei is
investigated. These weakly bound quantum systems present interesting examples
for the study of the interdependence between the deformation of the core and
the particles in the halo. Magnesium and neon isotopes are studied and detailed
results are presented for the deformed neutron-rich and weakly bound nuclei
42Mg. The core of this nucleus is prolate, but the halo has a slightly oblate
shape. This indicates a decoupling of the halo orbitals from the deformation of
the core. The generic conditions for the existence of halos in deformed nuclei
and for the occurrence of this decoupling effect are discussed.
