Effect of P addition on the structure and magnetic properties of melt-spun Fe–Pt–B alloy

The structure, thermal stability and magnetic properties of melt-spun Fe55Pt25B20−xPx (x = 0–5) alloys have been investigated. Addition of P increases the amorphous-forming ability of an Fe55Pt25B20 alloy, leading to the formation of the full amorphous phase. After annealing, the homogeneous nanosized structure consisting of hard L10-FePt and soft Fe2B magnetic phases with average grain size of ∼40 nm are obtained for the alloys with x = 0 and 2, while a L10-FePt/Fe2B nanocomposite structure with an average grain size of ∼80 nm is obtained for the alloy with x = 5. As the P content increases, the coercivity (iHc) of the L10-FePt/Fe2B nanocomposite alloys significantly increases, the remanence (Br) decreases. The alloy with x = 5 shows the largest iHc of 12.1 kOe, while the alloy with x = 2 exhibits higher Br of 53.5 emu/g and better demagnetization curve squareness, which is due to the enhancement in exchange coupling among the uniformly distributed nanosized Fe2B and L10-FePt phases.

► Addition of P increases the amorphous-forming ability of Fe–Pt–B alloys.
► Nanocomposite structure with L10-FePt and Fe2B phases is obtained for the alloys after annealing.
► Coercivity of the L10-FePt/Fe2B nanocomposite alloys is enhanced with increasing P content.
► Fe55Pt25B15P5 alloy exhibits high coercivity of 12.1 kOe.