Neutron diffraction study of the TbFeSi2-type NdMnCu0.5Ge1.5-xSix (0<=x<=1.5) solid solution

Antiferromagnetic TbFeSi2-type NdMnCu0.5Ge1.5-xSix compounds have been investigated by bulk magnetometric measurements and neutron diffraction. The Neel temperatures decrease from 370 K (x=0) to 200 K (x=1.5). The (010) Mn planes are antiferromagnetic in the germanium rich compounds (x less than or equal to 0.3), and become ferromagnetic in the silicon rich compounds (x>1.2). In the intermediate range (0.4<x<1.2), the compounds display more complicated magnetic structures with ''mixed'' Mn planes and/or helimagnetic arrangements. Whatever the concentration x, the Nd sublattice orders around T-t approximate to 70 K. The magnetic behaviour of the Mn sublattice is compared to that observed in the RMnCu0.5Ge1.5 and closely related RMnSi, RMn2Ge2, and RMnSi2 compounds. The various magnetic arrangements observed in NdMnCu0.5Ge1.5-xSix and RMnSi2 compounds are connected with modifications in the chemical bond in each series. (C) 1997 Elsevier Science S.A.