Nanostructured D022-Mn2Ga Alloys with High Magnetization and Coercivity

Nanostructured Mn 2 Ga alloys with the majority D0 22 phase have been prepared by subjecting ball-milled powders with micron size grains to the supercritical conditions of fluids at high pressure of 850 psi and temperature of 250 °C. The use of supercritical fluids was found to lead to a reduction of grain size from microscale to nanoscale. The supercritically treated samples show a homogeneous microstructure with an average grain size of 35 nm. The magnetic properties show an enhancement of magnetization and coercivity with values M S and H C of 55 emu/g and 4.7 kOe, respectively. This new method of enhancing the coercive field by a factor of more than two via the reduction of grain size to nanoscale opens new routes for rare-earth-free permanent magnet development.