Magnetic form factor of the heavy fermion compounds CeCu2Ge2 and CeCu1.9Ni0.1Ge2

CeCu 2 Ge 2 and CeCu 1.9 Ni 0.1 Ge 2 are heavy fermion compounds that order in incommensurate magnetic structures at low temperatures. The neutron magnetic form factor of single crystalline samples has been established by polarized neutron diffraction in the paramagnetic, as well as within the magnetically ordered state. For both compounds the neutron magnetic form factor could be reasonably well described within the dipole approximation but is also in accord with a Γ 7 -ground state as proposed on the basis of inelastic neutron scattering experiments. The present polarized neutron diffraction study shows that the ordered magnetic moment of CeCu 2 Ge 2 is extremely stable against any change of temperature or magnetic field and further remains almost unaltered by alloying of 5% Ni.