ANTIFERROMAGNETIC FORM-FACTOR OF SR2 CUO2CL2

Neutron diffraction techniques have been used to study the antiferromagnetic form factor of Sr2CuO2Cl2, which has the body-centered-tetragonal (I4/mmm) K2NiF 4-type structure (the same as that of tetragonal La 2CuO4 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 ((1)/(2) (1)/(2) 0), ((1)/(2) (1)/(2) 2), ((1)/(2) (1)/(2) 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 La 2CuO4. 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.