The antiferromagnetic form factor of La₂NiO₄

Neutron-diffraction techniques have been used to study the antiferromagnetic form factor of a La₂NiO₄ single crystal at 15 K. The antiferromagnetic form factor was obtained by measuring the integrated intensities of 16 magnetic reflections. A plateau is clearly seen at low Q (up to 3 Å^-1) in the experimentally determined form factor, similar to those observed for La₂CuO₄ and Sr ₂CuO₂Cl₂. As in the case of these latter compounds, the fit of the experimental data by a Ni²⁺ ionic form factor is not satisfactory. The experimental data are compared with a recent spin-polarized band calculation and with a covalency model.