The substitution of silicon for germanium in Mn-5 Ge-3 leads to a decr
ease in the magnetization for x < 0.7 and then to phase transition tow
ard a non-collinear antiferromagnetic order for Mn5Si3. The magnetic p
roperties of Mn5Ge3 and Mn-5(Ge0.5Si0.5)(3) are analyzed by means of b
and structure calculations.