  We have determined the spatial distribution of the magnetisation induced by a
field of 9 T in the tetragonal phase of BaFe2As2 using polarised neutron
diffraction. Magnetic structure factors derived from the polarisation
dependence of the intensities of Bragg reflections were used to make a maximum
entropy reconstruction of the distribution projected on the 110 plane. The
reconstruction shows clearly that the magnetisation is confined to the region
around the iron atoms and that there is no significant magnetisation associated
with either the As or Ba atoms. The distribution of magnetisation around the Fe
atom is significantly non-spherical with a shape which is extended in the <111>
directions in the projection. These results show that the electrons which give
rise to the paramagnetic susceptibility are confined to the Fe atoms their
distribution suggests that they occupy 3d t_2g type orbitals with about 60% in
those of xy symmetry.
