Macroscopic Gradient Ordered α-Fe/Pr₂Fe₁₄B Nanocomposites with Ultrahigh Energy Density

Nanoparticle self-assembly enables the generation of complex ordered nanostructures with enhanced properties or new functionalities. However, the ordering is often limited to the micrometer scale with chemical strategies due to the relative weak supramolecular interactions that govern the self-assembly process. Here a physical strategy via temperature-gradient-assisted self-assembly is reported to create three-dimensional (3D) macroscopic ordered nanocomposites with different gradient variations in grain size, constituent content, and crystal orientation. The resulting α-Fe/Pr₂Fe₁₄B ordered nanostructure with reverse gradients in both the grain size and α-Fe content exhibits a record-high energy density of about 25 MGOe for isotropic α-Fe/Pr₂Fe₁₄B systems, approximately 130% higher than that of its disordered counterpart. Both experiments and micromagnetic simulations demonstrate that creating ordered nanostructures is an alternative approach to develop high-performance permanent-magnet materials. Our findings make a significant step toward creating 3D macroscopic ordered nanostructures and will stimulate the development of ordered nanomaterials.