Different magnetic behaviour of the Kondo compounds Al3Ce and Al11Ce3

Neutron diffraction experiments on the Al3Ce and Al11Ce3 compounds have been performed on the multidetector of the ILL high flux reactor. No magnetic structure has been detected on the Al3Ce compound down to 20 m K. This confirms the non-magnetic ground state of Al3Ce. For Al11Ce3, two magnetic structures have been observed: a ferromagnetic one at 4.2 K and an antiferromagnetic one at 2 K. The antiferromagnetic structure, which corresponds to a propagation vector (0, 0, 1/3), implies a strong reduction of the magnetic moment of determined sites; this reflects the Kondo character of the compounds. (orig.)