Microstructure and magnetic properties of nanocrystalline Fe-Pt-based ribbons

Abstract The structural and magnetic properties of FePt – magnetic nanocomposites prepared by isothermal annealing of melt-spun Fe52Pt28Nb2B18 and Fe51Pt27Nb2B20 ribbons are reported. As it was evidenced the as-cast samples consists of L10-FePt hard magnetic grains dispersed in a predominant soft magnetic matrix composed of A1 FePt, Fe2B and boron-rich (FeB)PtNb residual phases. The applied annealing procedure reflects in temperature-induced structural and magnetic transition of dominated A1 FePt phase into L10-FePt dependent on Fe-Pt composition. As it was shown the Fe52Pt28Nb2B18 ribbon annealed at 700 °C exhibit promising hard magnetic properties at room temperature manifested as reasonably high remanence to saturation ratio (Mr/Ms = 0.68); coercivity (Hc = 0.92 T) and (BH)max = 83 kJ/m3 parameter. Strong exchange coupling between both FePt – based hard and soft magnetic phases was demonstrated by a smooth demagnetizing curve.