NEUTRON-DIFFRACTION STUDY ON HP 13-TYPE M7-XMNXGE6 (M = CO, FE)

We have made neutron diffraction experiments for Fe7-xMnxGe6 with x = 2 and 4 and CO7-xMnxGe6 with x = 3.25, which have the hexagonal hp 13- type structure. It is determined by the Rietvelt analysis for the nucl ear reflection that the 1T(1) site is entirely occupied by Mn atoms an d the 6T(2) site by Fe or Co atoms and excess Mn atoms. The magnetic r eflection of Fe3Mn4Ge6 corresponds to the collinear antiferromagnetism with alternating ferromagnetic layers in which the magnetic moments o f the 1T(1) and 6T(2) sites are 2.5 and 1.8 mu(B)/(Mn or Fe) atom, res pectively. Magnetic structures of the other alloys are quite complicat ed. (C) 1998 Elsevier Science B.V. All rights reserved.