PURPOSE: To obtain a hexagonal lattice type and antiferromagnetic Invar type alloy with high machinability and a specified coefft. of thermal linear expansion by adding Fe to an Mn-Ge alloy and subjecting the resulting alloy to a specified heat treatment.

CONSTITUTION: A composition consisting of 20W33wt% Ge, 0.01W10% Fe and the balance Mn with inevitable impurities is melted at a high temp. such as ≥900°C, and cast, and the cast alloy is formed into a prescribed shape. This formed body is homogenized at 500°CW below the m.p. for 1minW500hr and cooled from the temp. at ≥0.7°C/hr cooling rate to produce a hexagonal lattice type crystal phase. Thus, -8×10-6W+8×10-6 coefft. of thermal linear expansion is shown at -50W+100°C. By said composition and heat treatment, an antiferromagnetic Invar type alloy with improved grindability is obtd.