Collapse of the uranium 5f moment in ferromagnetic URhGa under pressure investigated by XMCD at the U M4,5 edges

The aim of this proposal is to quantitavely determine with high accuracy the pressure dependence of the U 5f orbital and spin moments and their ratio in the ferromagnetic URhGa. The measurements of magnetic and thermodynamic properties led to conclude that the Curie temperature initially increases whereas the saturation moment decreases. This is a rather unexpected behavior for UTX (T- transition metal, X- p element) compounds. A vanishing U 5f is expected to occur at about 17 GPa. The vanishing U moment could be due either to a compensation of the orbital and spin contribution or to the occurence of a non- magnetic ground state. We propose to measure XMCD under pressure at the U M4,5 edges to conclude between these two scenarios.