NEUTRON-DIFFRACTION STUDY OF THE TB3MN4GE4 COMPOUND

The antiferromagnetic Tb3Mn4Ge4 compound (orthorhombic Zr3Cu4Si4-type structure) has been studied by magnetization measurement and neutron d iffraction. The Mn magnetic framework is built of antiferromagnetic Mn -Mn zig-zag chains aligned along [001] (mu(Mn)=3.36(9)mu(B) at 2 K). T he two terbium crystallographic sites are characterized by different m agnetic behaviours. The terbium in the 2d position, surrounded by a fe rromagnetic Mn environment, displays a rather large ordered moment at 300 K (mu(Tb)=3.66 mu(B)) while the ordered moment of the terbium in t he 4e position, in a more complicated environment, gets a significant value only at low temperature. The Tb moments are close to their theor etical values at 2 K. The magnetic behaviour of the Mn sublattice is d iscussed and compared to the magnetic behaviour observed in the relate d TbMnGe and RMnGe (R=La-Nd) compounds.