서강대학교

초록/요약

Nd2Fe14B is one of the most popular permanent magnet (PM) possesing best energy product (BH)max among the common PM materials. However, exchange-coupled nanocomposite magnets fabricated by embedding nanostructures of soft-phase magnetic materials in a hard-phase magnetic matrix manifest higher remanence and higher energy product. Here we present the fabrication of exchange coupled Nd2Fe14B/Fe-Co magnetic nanocomposites using gel-combustion and diffusion-reduction processes. Pre-fabricated CoFe2O4 nanoparticles (NPs) of ⁓5 nm diameter were incorporated into Nd-Fe-B oxide matrix duirng its synthesis by gel-combution. The obtained mixed oxide was further processed with oxidative annealing at 800 oC for 2 h and reductive annaling at 900 oC for 2 h to form Nd2Fe14B/Fe-Co nanocomposite. Nanocomposites with different mol% of soft-phase were prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM) to study their crystalline phase, morphology and magnetic behaviors. While the used synthesis process was found effective for spin coupling between the hard and soft-phase magnetic domains through exchange interaction, addition of 7.7 mol% of soft-phase was found optimum, producing a coercivity (Hc) of 5.6 kOe and remanence (Mr) of 54 emu/g in the exchange-coupled nanocomposite.