Positron annihilation behaviors and magnetic properties of single-phase Nd2Fe14B and nanocomposite Nd2Fe14B/alpha-Fe magnets

Positron annihilation behaviors have been studied in the single phase Nd2Fe 14B magnet and the nanocomposite Nd2Fe14B/alpha -Fe magnet, prepared by mel t spinning. The results showed that the number of vacancy-cluster at grain boundaries increases with increasing annealing temperature for the both typ es of magnets. The increase of this kind of defect can improve the coercivi ty of the single-phase magnet. Conversely, the increase of vacancy-cluster amount leads to decreasing of the coercivity for the nanocomposite magnet. It implies that the mechanism of dominant magnetic hardening for the two ty pes of magnets is different, and the domain walls pinning mechanism in the single-phase magnet and the reversal magnetization nucleation mechanism in the nanocomposite magnet operate, respectively.