Induced magnetization density in the 5f system UAl2

Using a polarized‐neutron diffractometer we have studied the induced magnetization density in the unit cell of the 5f system UAl2. Measurements have been made on single crystals at 4.2 K with an applied magnetic field of 42.5 kOe (induced magnetic moment 0.0344 μB per mole). Neutron wavelengths of 1.067 and 0.785 A and different crystal thicknesses have been used to correct for and eliminate any effects from extinction. The major part of the magnetization density appears as a contribution localized at the U site, exhibiting a form factor similar to that of the f3 free ion, and extrapolating in the forward direction to the value given by the bulk susceptibility. However, there are two interesting aspects of the density. First, the form factor points differs significantly from a smooth curve. This indicates asphericity in the 5f electron distribution arising from the crystalline environment of the U atoms. Second, and more unusual, finite magnetic scattering amplitudes have been observed for a series of reflections to which the centrosymmetric density at the U site cannot contribute. We consider this as strong evidence of noncentrosymmetric bonding involving the 5f–6d electrons.