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

We studied the phase composition, microstructures and magnetic properties o f melt-spun Pr-8.5(Fe0.8Co0.2)(86.5-x)CuxB5 (x=0, 0.5, 1.0, 2.0. 3.0) nanoc omposites. It was found that Cu addition suppresses the formation of Pr-2(C oFe)(17) phase and results in a two-phase mixture of alpha-(FeCo)/Pr-2(FeCo )(14)B. Transmission electron microscopy (TEM) and energy-dispersive X-ray analysis (EDX) demonstrate that Cu strongly segregates at intergranular reg ions, leading to drastic decrease of the grain sizes of both 2:14:1 phase a nd alpha-(FeCo) phase. Wohlfarth remanence analysis indicates that the impa ct 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 th e Curie temperature of 3:14:1 phase. The magnetic properties of B-r, H-c, a nd (BH)(max) of optimally processed Pr-8.5(Fe0.8Co0.2)(86.5-x)CuxB5 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 har d and soft magnetic grains and the decrease in saturation magnetization. A combination of H-i(c) = 7.4 kOe, B-r = 10.9 kG and (BH)(max) = 20.1 MGOe ha s been obtained in Pr-8.5(Fe0.8Co0.2)(86)Cu0.5B5 ribbon. Moreover, minor ad dition of Cu (x = 0.5) is effective in reducing the irreversible loss of in duction (h(irr)) of the studied Pr-2(FeCo)(14)B/alpha-(FeCo) nanocomposite magnets. (C) 2000 Elsevier Science S.A. All rights reserved.