  The magnetization behaviors of GdMn2Ge2 and TbMn2Ge2 in the bulk and in the
fine particles obtained by high-energy ball-milling are compared. Pronounced
modificayions in the spontaneous, remnent and high-field magnetization in the
fine particle form, attributable to Mn are observed. The results indicate that
the antiferromagnetism of Mn sub-lattice known for the bulk form in the range
100-300 K gets weakened in favor of ferromagnetism in the fine particles. On
the basis of this observation, we infer that there are other factors like size
(and possibly defects) also play a role to decide the exact nature of magnetic
ordering of Mn in this ternary family of compounds, contrasting the
traditionally held view that the basal plane Mn-Mn distance is the crucial
controlling parameter.
