Chemical synthesis and coercivity enhancement of Nd₂Fe₁₄B nanostructures mediated by non-magnetic layer

High-performance Nd₂Fe₁₄B magnets have been widely required in various fields recently due to the lightweight and miniaturization of devices. In this work, we synthesize Nd₂Fe₁₄B nanostructures with tunable magnetic properties through surfactant-assisted high energy ball milling (SAHEBM) process, achieving prominently enhanced coercivity by forming non-magnetic layers as grain boundary phase. When the reduction annealing process was carried out as pellet with Ca, the coercivity increased from 0.8 kOe to over 3 kOe as Nd₂Fe₁₄B powder, which is proved to be the contribution of the chemical diffusion of Nd elements and the formation of Nd-rich layer as magnetic insulating medium. In addition, two-dimensional graphene oxide (GO) was employed to build extra grain boundary, by which the coercivity of the core@dual-shell structure can achieve up to 8 kOe, tenfold of the original sample. The intrinsic mechanism indicated that the Nd-diffusion induced Nd-rich phase along with the reduced GO in the system could form non-magnetic layer as grain boundary and magnetically isolate the adjacent grains, significantly enhancing the exchange coupling effect. This work markedly opens up an effective approach for the chemical preparation of high-performance Nd₂Fe₁₄B nanostructured magnets, especially after post treatment, and gives an insight on the interactions at nanoscale.