Antiferromagnetic form factor of Sr₂CuO₂Cl₂

Neutron diffraction techniques have been used to study the antiferromagnetic form factor of Sr₂CuO₂Cl₂, which has the body-centered-tetragonal (Ι 4/mmm) K₂NiF₄-type structure (the same as that of tetragonal La₂CuO₄ but with the out-of-plane oxygens replaced by Cl and the La by Sr). The antiferromagnetic form factor was obtained at 15 K by measuring the integrated intensities of the (½ ½ 0), (½ ½ 2), (½ ½ 3), (³⁄₂ ³⁄₂ 0), (³⁄₂ ³⁄₂ 6), (³⁄₂ ⁵⁄₂ 1), (³⁄₂ ³⁄₂ 8), and (⁵⁄₂ ⁵⁄₂ 0) magnetic reflections of a single crystal of Sr₂CuO₂Cl₂. The experimentally determined magnetic form factor is similar to that of La₂CuO₄. The experimental data were compared with the Cu²⁺ magnetic form factor and with the results of band theoretical calculations. We find that the fit to the experimental data is improved if one assumes a dipolar spin polarization on the in-plane oxygen ions.