Magnetization densities and uranium form factors in UNiGa and UNiAl

The magnetization densities and the uranium form factors of the two compounds UNiGa (metamagnetic) and UNiAl (antiferromagnetic) have been determined by polarized neutron scattering. Both compounds crystallize in the noncentrosymmetric hexagonal space group P anti 62m. Two methods have been applied to analyze the flipping ratios: a direct least squares atomic model refinement, and the noncentrosymmetric maximum entropy Fourier inversion. Both methods have given almost equal induced magnetic moments (1.31μB for U, 0.03μB for Ni1, 0.12μB for Ni2 in the case of UNiGa, and 0.14 for U, 0.02 for Ni1 and 0.01 for Ni2 in the case of UNiAl). For both compounds the expression for the U form factor has been found to be the same: left angle j0 right angle +2.0 left angle j2 right angle slightly different from the U3+ free ion. Furthermore, the maximum entropy method has revealed, in each compound, the presence of small amounts of Ni interstitial atoms. (orig.)