Phase transformation in Mn3Ga considering different degrees of deformation

Abstract

Due to a strong structure-property relationship, the different Mn3Ga modifications (cubic, hexagonal and tetragonal) show distinctively different magnetic properties. However, the synthesis of Mn3Ga with specific target properties is complicated by contradictory reports on phase stability and insufficient understanding of phase formation. In this work, we describe the phase formation of bulk Mn3Ga at 400 °C in a time-resolved manner from 1 h to 14 days. Special emphasis is laid on how the evolution of phase composition and magnetic properties is affected by applying varied degrees of deformation prior to annealing (pre-processing). While carefully considering the structural relations between different Mn3Ga modifications, the impact of different defect types is explored. Among other deformation effects, we discovered a shear-induced back-and-forth transformation between the cubic and hexagonal structures. When annealing at 400 °C two different transformation pathways were identified, both terminating in tetragonal Mn3Ga as the low-temperature equilibrium phase. Our results suggest that the preferred transformation pathway is particularly determined by the density of stacking faults, due to their participation in formation of an intermediate phase. Thus, careful consideration of the pre-processing allows for improved control on phase formation in Mn3Ga, resulting in a purposeful tuning of its magnetic properties.