MAGNETIC NEUTRON POWDER DIFFRACTION ON SOME UCU2-XGA2-TYPE STRUCTURE(Y TERNARIES OF THE THCR2SI2)

The magnetic structures of seven different specimens of constitution U Cu2-xGa2+y were investigated by neutron powder diffraction. All specim ens were found to order antiferromagnetically below 50 K. For UCu1.66G a2.66 and UCu1.33Ga2.66, a simple magnetic structure of the type AFI w as observed where the magnetic unit cell is identical to the chemical one. In contrast, the ternaries UCu1.25Ga2.5, UCu1.33Ga2.5, UCu1.45Ga2 .5, UCu1.45Ga2.55 and UCu1.4Ga2.6 show a new type of antiferromagnetic ordering with a magnetic unit cell enlarged by a factor of four with respect to the chemical unit cell. (C) 1998 Elsevier Science B.V. All rights reserved.