Phase equilibria and magnetic properties in Mn-Ga-Cu ternary alloys

Phase equilibria at 600 and 800 °C and magnetic properties of some selected alloys in the low Ga portion of the Mn-Ga-Cu ternary system were investigated. It was clarified that the α-fcc (γMn, Cu) and β-bcc (δMn, Cu3Ga) phase exist in a wide composition range along the Ga-Cu side at 800 °C, while a very stable ternary compound, τ2 (Cu5Ga3Mn4, hP12), appears in the center of the low Ga region at 600 °C. It was also confirmed that all the β phase specimens quenched from 800 °C martensitically transform to the 2H, 2M or 6M phase with high density of stacking faults. In the Mn-19.0Ga-25.8Cu (at.%) martensite alloy followed by aging at 400 °C, a high coercivity of 11.7 kOe was detected, which may have resulted from the dispersion of the metastable ferrimagnetic Mn3Ga-D022 phase during the aging treatment.