MAGNETIZATION AND COERCIVITY OF MN3-DELTA-GA ALLOYS WITH A D0(22)-TYPE STRUCTURE

The DO22-type (Al3Ti-type) phase in the Mn-Ga system is ferrimagnetic; the spin direction is parallel to the tetragonal c axis. The Curie te mperature is about 765 K (for delta = 0.67), near the decomposition te mperature. We have prepared the DO22-type alloys by annealing the quen ched ingots of the high-temperature phase (gamma(Mn) phase) at 400 or 300 degrees C for a long time. The preparation becomes much easier if the ingots are powdered by filing before the annealing. The single-pha se specimens of Mn3-deltaGa were obtained in the composition range 0.1 5 less than or equal to delta less than or equal to 1.06. The coercivi ty of some specimens was so large that we measured the magnetization c urve in high magnetic fields up to 150 kOe. The room-temperature value s of saturation magnetization, remanent magnetization, and coercivity of the powder sample of the alloy with delta = 0.67 are 50 emu/g, 25 e mu/g, and 13.5 kOe, respectively. We have also studied the effect of m agnetic annealing during the transition from the gamma(Mn) phase to th e DO22-type phase and the effect of the addition of Fe to Mn3-deltaGa of the DO22-type phase. (C) 1996 American Institute of Physics.