Al substitution effects on phase stabilities and magnetic properties of tetragonal Mn3Ge

We have investigated Al substitution effects on phase stabilities and magnetic properties of Mn3Ge with tetragonal D022 structure. The lattice constant a is expanded, and the c is contracted by substituting Al for Ge. Consequently, the unit cell volume slightly increases with the increasing Al content, although Al atom has smaller ionic radius than Ge atom. These composition dependencies of the structural parameters are influenced by the number of the valence electrons rather than the ionic radius. Thermal stability of the D022 structure is enhanced by the Al substitution. The magnetic curves of the Al-substituted system mostly unchanged, suggesting that the structural properties such as the unit cell volume and the atomic distance between the Mn atoms play an important role for the magnetic properties of the alloy.