The effect of annealing time on the magnetic properties and microstructure of (Fe0.675Pt0.325)84B16 ribbons

Effect of annealing time on the magnetic properties and microstructure of (Fe0.675Pt0.325)84B16 ribbon has been studied. For the as-quenched ribbons (Vs=45 m/s) annealed isothermally at 500 °C, iHc increases from 0.05 kOe for the quenched ribbons to the optimal value of 7.5 kOe after 5 h annealing, but Br increases from 1.2 kG for the as-quenched ribbons to 7.5 kG after 5 h annealing at first, then decreases when the annealing time is over 6 h. From thermal magnetic analyzer (TMA) and high resolution transmission electron microscope (HRTEM), magnetically soft Fe2B and Fe3B were found to coexist with magnetically hard γ1-FePt phase in the ribbons after suitable annealing. The existence of sufficient fine Fe3B with Fe2B phases and the well exchange coupling effect between hard and soft phases are the main cause of the improved remanence and magnetic energy product of the ternary (Fe0.675Pt0.325)84B16 ribbons.