On the evolution of the ground state in the system UxLa1−xS: Polarized neutron diffraction and X-ray magnetic circular dichroism study

In the UxLa1−xS system there is an abrupt loss of the long-range ferromagnetic ordering found in pure US at a critical concentration xc ∼ 0.57, which is far above the percolation limit. As the magnetic ground state in such a system can be strongly affected by small variations of the 5f localization, we have investigated a set of samples with different x by polarized neutron diffraction and X-ray magnetic circular dichroism (XMCD). The neutron results are consistent with early measurements performed on pure US. Even at the lowest U content (x = 0.15, below xc) the shape of the induced form factor (f(Q)) is comparable with that found for x = 1 and is well reproduced by either a U or a U state. The ratio between the orbital and the effective spin moments in the XMCD measurements confirms this result, but the evolution of the shape at the M5 edge suggests an abrupt change in the distribution of the electrons (holes) in the 5f density of states around xc. PACS. 87.64.Ni Optical absorption, magnetic circular dichroism, and fluorescence spectroscopy – 75.25.+z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.)