Microstructure and Improved Coercivity of Mn1.33Ga Nanoflakes by Surfactant-Assisted Ball Milling

Tetragonal polycrystalline Mn-Ga nanoflakes with a nominal composition of Mn_1.33Ga were prepared by the surfactant-assisted high-energy ball milling method, and the effects of milling time and annealing treatment on structure and the magnetic properties were also investigated in detail. The irregular Mn_1.33Ga flakes show typical shape anisotropy and a high aspect ratio with thicknesses in the range of 100 nm ~ 3 μm. Crystalline grain is reduced to 10 nm when increasing the milling time above 4 h. Coercivity is greatly improved, and the highest coercivity of 7.2 kOe is obtained for flakes milled for 2 h, but the saturation magnetization, Ms, and remanence, Mr, decrease sharply during the ball milling process. Medium-temperature annealing is beneficial to the crystallization and the enhancement of magnetization. After annealing at 773 K for 30 min, Ms and Mr are recovered to 68 and 41 emu/g, respectively; and the (BH)max can reach 2.3 MGOe which is comparable with that of 2.5 MGOe for films or microparticles.