High coercivity in FePt-based bulk magnets

The purpose of this study is to demonstrate the process technology which can yield bulk shaped FePt permanent magnets with a large coercivity. Rapid quenching of the ribbons and the ball milling route were adopted to process nanocrystalline powders, and annealing were performed in the temperature range 500-700 °C. Then, the as-milled powders were subsequently consolidated by spark plasma sintering method. Constituent phases were examined by X-ray diffraction and microstructural studies were carried out by transmission electron microscopy. Magnetic properties were evaluated using a vibrating sample magnetometer and SQUID magnetometer. The compositions selected were: (i) equiatomic FePt, (ii) Fe₃₅Pt₃₅P₃₀ and (iii) Fe₅₃Pt₄₄C₃. The selection of C-containing composition was based on the expectation that carbon will restrict the growth of FePt particles and hence will enhance the coercivity.