Magnetic properties and structure of Nd-(Fe,B) nanocomposite alloys with fixed Fe/B ratios at 4-14

Magnetic properties and nanostructure of pseudobinary Nd-(Fe,B) alloys with lived Fe/B ratios of 4, 6, 8, 10, l4, respectively and Nd=3 to II at %, prepared by melt-spinning and rapid thermal annealing (RTA), were investigated. Magnetic properties were found to depend on nanostructure, particularly the size and size distribution of hard and soft phases, which were in turn determined by Nd contents and Fe/B ratios together with RTA processing. The maximum energy products, (BH)(max), of the optimally RTA treated 11 at.%Nd flakes with Fe/B=IO and I4 are 19 MGOe and l8.8MGOe, respectively. However, the remanence decreases with increasing Nd contents due to the decreasing amount of Fe nanocrystal. The Fe/B=6 alloys with Nd < 6 at.% showed very low intrinsic coercivity (iHc) and (BH)(max), which were attributed mainly to impurity phases, typically Nd2Fe23B3 and Nd1.1Fe4B4. The reversible and irreversible magnetization behaviors were also studied in order to qualify the exchange coupling interaction between hard and soft phases of alloys, The variation in nucleation field at the same Fe/B ratio of 14 was found to depend on volume fraction of hard phase formation as well as the size distribution of the two phases.