Magnetic form factor in CeRu2Si2 on crossing its metamagnetic transition

The magnetic form factor of the heavy fermion compound CeRu2Si2 was measured by polarized neutron diffraction in the Pauli paramagnetic phase and above the metamagnetic transition. The magnetization density is characteristic of 4f electrons in both phases with an almost pure |5/2,5/2 ground-state wavefunction. The only field effect observed in this experiment corresponds to a nonlinear variation of the magnetization of the 4f electrons.