Fabrication of Mn-(Bi, Ga) based hard magnetic nanocomposites

The hard and soft magnetic nanoparticles of Mn-(Bi, Ga) and Fe-Co, respectively, were prepared by using a high energy ball milling method. These nanoparticles were then mixed together with different ratios and subsequently annealed in various conditions of temperature and time to make nanocomposite magnets. The coercivity Hc and maximum energy product (BH)max of these magnets depend on the nanoparticle size and on the ratio of the hard/soft magnetic phases. The annealing process plays an important role for exchangecoupling between the hard and soft magnetic phases. With sizes in a range of 40-60 nm, the Mn-(Bi,Ga) nanoparticles reveal high coercivity (Hc > 12 kOe) to be a potential rare-earth-free hard magnetic phase for producing nanocomposite magnets. Quite high coercivities, Hc > 4 kOe, and maximum energy products, (BH)max > 4 MGOe, have been achieved for this kind of rare-earth-free nanocomposite magnets.