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.

Engineering Bulk, Layered, Multicomponent Nanostructures with High Energy Density.

The precise control of individual components in multicomponent nanostructures is crucial to realizing their fascinating functionalities for applications in electronics, energy-conversion devices, and biotechnologies. However, this control remains particularly challenging for bulk, multicomponent nanomaterials because the desired structures of the constitute components often conflict. Herein, a strategy is reported for simultaneously controlling the structural properties of the constituent components in bulk multicomponent nanostructures through layered structural design. The power of this approach is illustrated by generating the desired structures of each constituent in a bulk multicomponent nanomaterial (SmCo + FeCo)/NdFeB, which cannot be attained with existing methods. The resulting nanostructure exhibits a record high energy density (31 MGOe) for this class of bulk nanocomposites composed of both hard and soft magnetic materials, with the soft magnetic fraction exceeding 20 wt%. It is anticipated that other properties beyond magnetism, such as the thermoelectric and mechanical properties, can also be tuned by engineering such layered architectures.

Controllably Manipulating Three-Dimensional Hybrid Nanostructures for Bulk Nanocomposites with Large Energy Products.

Hybrid nanostructures that comprise two or more nanoscale functional components are fascinating for applications in electronics, energy conversion devices, and biotechnologies. Their performances are strongly dependent on the characteristics of the individual components including the size, morphology, orientation, and distribution. However, it remains challenging to simultaneously control these structural properties in a three-dimensional (3D) hybrid nanostructure. Here, we introduce a robust strategy for concurrently manipulating these characteristics in a bulk SmCo/Fe(Co) nanocomposite. This method can tune nanocrystals in size (down to sub-10 nm), morphology (sphere, rod, or disc), and crystallographic orientation (isotropic or anisotropic). We have therefore achieved the desired nanostructures: oriented hard magnetic SmCo grains and homogeneously distributed soft magnetic Fe(Co) grains with high fractions (∼26 wt %) and small sizes (∼12.5 nm). The resulting anisotropic nanocomposite exhibits an energy product that is approximately 50% greater than that of its corresponding pure SmCo magnet and 35% higher than the reported largest value in isotropic SmCo/Fe(Co) systems. Our findings pave a new way to manipulating 3D hybrid nanostructures in a controllable manner.

Fast fabrication of a hierarchical nanostructured multifunctional ferromagnet.

Materials with multifunctionality affect society enormously. However, the inability to surmount multiple functionality trade-offs limits the discovery of next-generation multifunctional materials. Departing from conventional alloying design philosophy, we present a hierarchical nanostructure (HNS) strategy to simultaneously break multiple performance trade-offs in a material. Using a praseodymium-cobalt (PrCo5) ferromagnet as a proof of concept, the resulting HNS outperforms contemporary high-temperature ferromagnets with a 50 to 138% increase in electrical resistivity while achieving their highest energy density. Our strategy also enables an exceptional thermal stability of coercivity (-0.148%/°C)-a key characteristic for device accuracy and reliability-surpassing that of existing commercial rare-earth magnets. The multifunctionality stems from the deliberately introduced nanohierarchical structure, which activates multiple micromechanisms to resist domain wall movement and electron transport, offering an advanced design concept for multifunctional materials.

Directional Magnetization Reversal Enables Ultrahigh Energy Density in Gradient Nanostructures.

High-performance ferromagnetic materials are essential for energy conversion and electronic devices. However, the random and nonuniform magnetization reversal in ferromagnetics limits their performance that can be achieved. Here, through both micromagnetism simulations and experiments, a directional magnetization reversal that initiates first from large grains toward smaller ones is discovered by engineering Nd2 Fe14 B/α-Fe gradient nanostructures. Such directional magnetization reversal enables a rare combination of high magnetization and large coercivity, thus leading to a record-high energy density (26 MG Oe) for isotropic permanent magnetic materials, which is ≈50% higher than that of its gradient-free counterpart. The unusual magnetization reversal originates from an ordered arrangement of grain sizes in the gradient material, where the large grains have a lower reversal field than that of the smaller ones. These findings open up new opportunities for developing high-performance magnetic materials.