Chemical synthesis of Nd 2 Fe 14 B/Fe-Co nanocomposite with high magnetic energy product.

Nd 2 Fe 14 B is one of the most popular permanent magnets (PMs) possessing the best energy product (BH) max among the common PM materials. However, exchange-coupled nanocomposite magnets fabricated by embedding nanostructures of soft-phase magnetic materials into a hard-phase magnetic matrix manifest higher remanence and a higher energy product. Here we present the fabrication of exchange coupled Nd 2 Fe 14 B/Fe-Co magnetic nanocomposites using gel-combustion and diffusion-reduction processes. Pre-fabricated CoFe 2 O 4 nanoparticles (NPs) of ∼5 nm diameter were incorporated into a Nd-Fe-B oxide matrix during its synthesis by gel-combustion. The obtained mixed oxide was further processed with oxidative annealing at 800 °C for 2 h and reductive annealing at 900 °C for 2 h to form a Nd 2 Fe 14 B/Fe-Co nanocomposite. Nanocomposites with different mol% of soft-phase were prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and physical property measurement system (PPMS) to study their crystalline phase, morphology and magnetic behavior. Addition of 7.7 mol% of soft-phase was found to be optimum, producing a coercivity ( H c ) of 5.6 kOe and remanence ( M r ) of 54 emu g -1 in the nanocomposite.