Phase transformation and magnetic properties of ferromagnetic Cu-Mn-Ga alloys

Phase transformation, microstructure and magnetic properties were investigated for Cu-(11-14) mol%Mn-20mol%Ga. The structures of the magnetic domains were also investigated by Lorentz microscopy and electron holography. Plate-like martensite phase(ζ_M, ordered hcp) was observed in as-quenched Cu-12 mol%Mn-20mol%Ga. Phase transformation from ζ_M martensite to ζ phase(hcp) occurred at around 540K on heating. The ζ phase decomposed into ζ″ (ordered hcp) and β(bcc) phase at around 700 K, then became the single β phase at around 840 K. By subsequent slow cooling, ζ phase was observed at room temperature. The results obtained from Lorentz microscopy and electron holography revealed that the twin plates of ζ_M martensite and the magnetic domain have one-to-one correspondence, suggesting high magneto-crystalline anisotropy energy of the martensite phase. The saturation magnetization and the Curie temperature increased with Mn content.