Effects of solvent and annealing on phase evolutions and magnetic properties of Nd2 (Fe, Co)14C hard magnetic powders prepared by mechanochemical method

Nanocrystalline Nd2 (Fe, Co)14C materials were synthesized by a mechanochemical method. Ball milling in organic solvent (hydrocarbon), Nd15Fe80.6Co4B0.4 alloy disproportionated into NdH2+δ, α-Fe (Co) and Fe7C3 phases. H2 was released from the NdH2+δ and Nd2 (Fe, Co)14C hard magnetic powders were obtained during the subsequent annealing under vacuum. The effects of hydrocarbon solvent species and annealing condition on phase evolutions and magnetic properties were studied systematically. It is found that the n-hexane is more easily decomposed and makes the disproportion reaction more completed than other common hydrocarbons, which favor the formation of permanent magnetic Nd2 (Fe, Co)14C phase. Scanning electron microscope and Henkel plot analysis verified microstructural and intergranular exchange coupling can be well controlled by the annealing process. The optimum magnetic properties with remanent magnetization 4πMr of 7.35 kG, maximum energy product (BH)max of 12.3 MGOe and coercivity iHc of 16.2 kOe were obtained in the sample ball milled in n-hexane and annealed at 800 °C for 2 min with a heating rate of 10 °Cs−1. The systemical study shows that this method is a promising way to synthesize nano-sized Nd2 (Fe, Co)14C hard magnetic powder suitable for the manufacture of bond permanent magnet. Keywords: Permanent magnet, Mechanochemical, Nanocrystalline, Exchange coupling

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