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

Phase transformation, microstructure and magnetic properties of Cu-(11-14)mol%Mn-20 mol%Ga alloy were investigated. Magnetic domain structures were also investigated by the Lorentz microscopy and electron holography. Plate-like martensite phase (ζ _M. ordered hep) was observed in as-quenched Cu-12 mol%Mn-20 mol%Ga. Phase transformation from ζ _M martensite to ζ phase (hcp) occurred at around 540 K on heating. The ζ phase decomposed into β (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. Results of the Lorentz microscopy and electron holography revealed that the twin plates of CM martensite and magnetic domains have one-to-one correspondence, suggesting high magneto-crystalline anisotropy energy of the martensite phase. Saturation magnetization and Curie temperature increased with Mn content.