Lattice Distortion and Multiple Spin Density Wave State in γMn Alloys

Abstract

The relation between tetragonal lattice distortion observed in Mn-rich γMn alloys such as MnNi, MnFe and MnCu and their magnetic structures is investigated on the basis of the Landau expansion of free energy. By taking into account a coupling between lattice distortions and three magnetic order parameters specifying the first-kind antiferromagnetic ordering on the fcc lattice, possible phase diagrams in the temperature-composition plane are discussed. Observed various types of phase diagram for lattice distortion including the orthorhombic phase in γMnNi alloys are shown to be well explained and the type of multiple spin density wave state for each phase is predicted.