STRUCTURE AND MAGNETIC-ORDERING IN THE DEFECT COMPOUND ERGE1.83

The crystal structure and the magnetic ordering of the novel orthorhom bic compound ErGe2-x has been studied by neutron powder diffraction an d magnetic measurements. The crystal structure belongs to the DyGe1.85 -type (space group Cmc2(1)). ErGe2-x (x=0.17(2)) orders antiferromagne tically below T-n=6 K with a uniaxial magnetic moment arrangement. The magnetic cell has the same size as the chemical unit cell (q=0). The magnetic space group is Cmc2(1) (Sh(36)(173)). At T=1.5 K the magnetic moments of the two erbium sites have the same ordered magnetic moment value of 7.63(6) mu(B)/Er and are coupled antiferromagnetically along the a direction.