Beneficial effects of Cu substitution on the microstructures and magnetic properties of Pr 2(FeCo) 14B/α-(FeCo) nanocomposites

Abstract

We studied the phase composition, microstructures and magnetic properties of melt-spun Pr 8.5(Fe 0.8Co 0.2) 86.5− x Cu x B 5 ( x=0, 0.5, 1.0, 2.0, 3.0) nanocomposites. It was found that Cu addition suppresses the formation of Pr 2(CoFe) 17 phase and results in a two-phase mixture of α-(FeCo)/Pr 2(FeCo) 14B. Transmission electron microscopy (TEM) and energy-dispersive X-ray analysis (EDX) demonstrate that Cu strongly segregates at intergranular regions, leading to drastic decrease of the grain sizes of both 2:14:1 phase and α-(FeCo) phase. Wohlfarth remanence analysis indicates that the impact of Cu addition on the strength of exchange coupling interactions between hard and soft magnetic phases in the ribbons is determined by two opposite factors: (1) grain refinement and (2) grain isolation especially at higher Cu content. A small amount of Cu addition ( x=0–3.0) has little effect on the Curie temperature of 2:14:1 phase. The magnetic properties of B r, i H c, and ( BH) max of optimally processed Pr 8 5(Fe 0 8Co 0.2) 86.5− x Cu x B 5 ribbons initially increase with increasing Cu content from x=0 to 0.5 but all of them decrease drastically with further increasing Cu content, which can be mainly attributed to the variation of exchange coupling effect between hard and soft magnetic grains and the decrease in saturation magnetization. A combination of i H c=7.4 kOe, B r=10.9 kG and ( BH) max=20.1 MGOe has been obtained in Pr 8.5(Fe 0.8Co 0.2) 86Cu 0.5B 5 ribbon. Moreover, minor addition of Cu ( x=0.5) is effective in reducing the irreversible loss of induction ( h irr) of the studied Pr 2(FeCo) 14B/α-(FeCo) nanocomposite magnets.