Abstract
The Fe64B22.8Nd6.6Y3.9Nb2.7 nanocomposite permanent magnets in the form of rods of 2 mm in diameter and 25 mm in length have been prepared by annealing the amorphous precursors. The phase evolution, microstructure, and magnetic properties of Fe64B22.8Nd6.6Y3.9Nb2.7 nanocomposite permanent magnets have been investigated by x-ray diffractometry, transmission electron microscopy, and magnetometry techniques. The exchange coupling between the magnetically soft and hard magnetic phase is evidenced by the delta M curves. The hard magnetic properties of the nanocomposites were found to be sensitive to the annealing process. The microstructure of the annealed nanocomposite consists of magnetically soft alpha-Fe (15-25 nm) and Fe3B (25-35 nm) grains and hard magnetic Nd2Fe14B (45-55 nm) grains. The optimum hard magnetic properties, such as H-j(c) = 961.6 kA/m (12.0 kOe), B-r = 0.65 T (6.5 kG), and BHmax = 65.17 kJ/m(3) (8.19 MGOe), were obtained by annealing the alloy at 700 degrees C for 15 min and are related to the more refined nanostructure leading to strong exchange coupling between the soft and hard magnetic grains. Annealing above 700 degrees C induces a decoupling effect due to the coarsening of soft and hard magnetic phases.