The influence of milling and annealing on the structural and magnetic behavior of Nd2Fe14B/alpha-Fe magnetic nanocomposite
Résumé
Exchange coupled Nd2Fe14B/22 wt% alpha-Fe hard/soft magnetic nanocomposite was obtained by mechanical milling and subsequent annealing. In order to improve the crystallinity of hard magnetic phase and in the same time to hinder the increase of crystallites size of the soft magnetic phase, the rapid annealing was performed at temperatures from 700 to 800 degrees C for duration up to 2.5 min. The structural and microstructural properties were determined from X-ray diffraction (XRD), the qualitative and quantitative composition was evaluated by X-ray Photoelectron Spectroscopy (XPS) and magnetic behavior was estimated from hysteresis curves and dM/dH vs. H curves. The present results on soft/hard exchange coupling can be understood from the competition between the crystallinity of the hard phase and the crystallite size of soft magnetic phase resulting by annealing of milled nanocomposite. The best coercivity was obtained for samples annealed at 700, 750 and 800 degrees C for 2, 1.5 and 1 min respectively.