High Coercivity in Annealed Melt-Spun Mn-Ga Ribbons

Mn-Ga is a complex system due to the large number of phases which can be formed at different alloy compositions. In this paper, we present a simple method to prepare Mn_2-3Ga alloys with a majority D0₂₂ phase by heat treating melt-spun ribbons. X-ray diffraction results show the formation of D0₂₂ after annealing the as-prepared ribbons with the D0₁₉ structure at 450 °C for different times. This transformation results in a high H_C of 8 kOe and a magnetization of 10 emu/g, at room temperature. SEM images in the as-prepared ribbons show the presence of a microrod-like D0₁₉ microstructure with the size of the rods in the range of 0.5-1 μm. This homogeneous structure, after annealing for long time is transformed to D0₂₂ spherical shape nanoparticles with an average size below 100 nm. Samples annealed further at 600 °C for 16 h showed a higher magnetization of 18 emu/g.