Neutron diffraction study of the electronic structure of high-T[subscript c] superconductor-related compounds

Neutron diffraction techniques have been used to study the electronic structure of La[subscript]2NiO[subscript]4 and Sr[subscript]2CuO[subscript]2Cl[subscript]2 by measuring the antiferromagnetic form factor of the single-crystal samples at 15 K. The antiferromagnetic form factor was obtained from the integrated intensities of several magnetic reflections. In both cases, the experimentally determined form factor exhibits a plateau at low Q values (up to 3 A[superscript]-1), similar to that observed for La[subscript]2CuO[subscript]4. Detailed modelling of the experimental data of these three compounds suggests that the observed plateau may be accounted for by including the covalency effects in the Ni-O or Cu-O plane. The experimental data are also compared with spin-polarized band calculations