Novel exchange-coupled SmFe3/α-Fe nanocomposite magnets fabricated by magnetic annealing

1.SmFe3/α-Fe nanocomposite magnet is fabricated by magnetic annealing.2.Magnetic behavior is studied by analyzing hysteresis loops and Henkel plots.3.Magnetic annealing leads to strong exchange coupling and enhanced (BH)max.4.α-Fe about 3–8 nm with high volume fraction is obtained by magnetic annealing.

A new nanocomposite magnet containing exchange-coupled SmFe3 and α-Fe phases has been successfully fabricated via melt spinning followed by magnetic annealing at 450–470 °C for 10 min. These SmFe3/α-Fe magnets show remarkably high remanent ratio, Mr/Ms, up to 0.93 and display a smooth single-phase-like loop with excellent rectangularity. In comparison, the non-field treated ones exhibit much lower Mr/Ms values and show a distinctive kink in the demagnetization curve due to the decoupling of the nanograins. The Henkel plot and microstructural examination confirm that magnetic annealing leads to much stronger intergranular exchange coupling, which is attributed to the formation of a magnetic-field-induced microstructure consisting of the SmFe3 hard phase with diameters of 80–100 nm and the α-Fe soft phase with size of about 3–8 nm. An enhanced energy product of 13.0 MGOe has been obtained in the ribbon magnetically annealed at 470 °C, which is about 60% higher than that of the ribbon annealed without a magnetic field.