Nanocomposite magnets have attracted considerable attention as a probable new generation of permanent magnets with a potential theoretical maximum energy product of 1 MJ/m³ due to remanence enhancement resulting from intergrain exchange interactions between magnetically
soft and hard grains. However, the presence of soft phase increases remanence but coercive field is significantly decreased. Alloys with Nd content higher than 11%(atom fraction), i.e., close to the stoichiometry composition of Nd₂Fe₁₄B, are being studied to further improve coercivity. Nanocrystalline Nd_xFe_94−xB₆(x=11.0—16.8) alloys were prepared by melt–spinning at a rate of 22 m/s cooperating with subsequent annealing. The effects of Nd content on microstructure, magnetic properties, exchange coupling interactions and coercivity mechanism have been studied by X–ray diffraction (XRD), differential scanning calorimeter (DSC), high resolution scanning electron microscope (HRSEM) and vibrating sample magnetometer (VSM). The intrinsic coercivity Hci increases from 601.3 kA/m for x=11.0 to 1277.3 kA/m for x=16.8 monotonously, and on the contrary, the remanent polarization Jr reduces from 1.047 T for x=11.0 to 0.721 T for x=16.8. The maximum energy product (BH)_max first increases
and then reduces with increasing Nd content. The optimum magnetic properties with J_r=0.992 T, H_ci=727.9 kA/m and (BH)_max=137.2 kJ/m³ are achieved by annealing melt–spun Nd_11.8Fe_82.2B₆ ibbons. Although the exchange coupling interactions are degraded by increasing Nd content in the ribbons, it is still relatively strong for the alloy with x=16.8. The coercivities of alloys are determined mainly by pinning field. Nd content almost does not influence microstructure under optimal annealing conditions. The microstructral model of nanocrystalline Nd–Fe–B with different Nd content is presented and used to analyze the effect of Nd content on magnetic properties and exchange coupling effect well.