Magnetization densities and uranium form factors in UNiGa and UNiAl

Abstract

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 6 2m. 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 (1.31 μ B for U, 0.03 μ B for Ni1, 0.12μ B for Ni 2 in the case of UNiGa, and 0.14 for U, 0.02 for Ni 1 and 0.01 for ni 2 in the case of UNiAl). For both compounds the expression for the U form factor has been found to be the same: 〈 j 0〉 + 2.0 〈 j 2〉 slightly different from the U 3+ free ion. Furthermore, the maximum entropy method has revealed, in each compound, the presence of small amounts of Ni interstitial atoms.