Chemical synthesis of Nd2Fe14B/Fe3B nanocomposites

Magnetic Nanostructures: Rational Design and Fabrication Strategies toward Diverse Applications

In recent years, the continuous development of magnetic nanostructures (MNSs) has tremendously promoted both fundamental scientific research and technological applications. Different from the bulk magnet, the systematic engineering on MNSs has brought a great breakthrough in some emerging fields such as the construction of MNSs, the magnetism exploration of multidimensional MNSs, and their potential translational applications. In this review, we give a detailed description of the synthetic strategies of MNSs based on the fundamental features and application potential of MNSs and discuss the recent progress of MNSs in the fields of nanomedicines, advanced nanobiotechnology, catalysis, and electromagnetic wave adsorption (EMWA), aiming to provide guidance for fabrication strategies of MNSs toward diverse applications.

Synthesis of mesoscopic particles of multi-component rare earth permanent magnet compounds

Multielement rare earth (R)-transition metal (T) intermetallics are arguably the next generation of high-performance permanent magnetic materials for future applications in energy-saving and renewable energy technologies. Pseudobinary Sm2Fe17N3 and (R,Zr)(Fe,Co,Ti)12 (R = Nd, Sm) compounds have the highest potential to meet current demands for rare-earth-element-lean permanent magnets (PMs) with ultra-large energy product and operating temperatures up to 200°C. However, the synthesis of these materials, especially in the mesoscopic scale for maximizing the maximum energy product (B H m a x ), remains a great challenge. Nonequilibrium processes are apparently used to overcome the phase-stabilization challenge in preparing the R-T intermetallics but have limited control of the material's microstructure. More radical bottom-up nanoparticle approaches based on chemical synthesis have also been explored, owing to their potential to achieve the desired composition, structure, size, and shape. While a great achievement has been made for the Sm2Fe17N3, progress in the synthesis of (R,Zr)(Fe,Co,Ti)12 magnetic mesoscopic particles (MMPs) and R-T/T exchange-coupled nanocomposites (NCMs) with substantial coercivity (H c ) and remanence (M r ) , respectively, remains marginal.

First-order-reversal-curve analysis of rare earth permanent magnet nanostructures: insight into the coercivity enhancement mechanism through regulating the Nd-rich phase

The coercivity enhancement mechanism of Nd₂Fe₁₄B-based nanostructures with Nd-rich phase is revealed by first-order-reversal-curve diagram, which is that increased Nd-rich phase content leads to optimized magnetic interactions and microstructure.

Rare earth permanent magnetic nanostructures: chemical design and microstructure control to optimize magnetic properties

The routes for the optimization of the magnetic properties of rare earth permanent magnetic nanostructures are discussed, i.e. the control of microstructure, such as size and shape as well as the exchange-coupling interactions.

Insight into the Property Enhancement Mechanism of Chemically Prepared Multi-Main-Phase (Nd,Ce)2Fe14B

Nd₂Fe₁₄B has attracted intensive attention because of its excellent magnetic properties since 1980s. However, large demands for the expensive rare earth (mainly refers to Nd/Pr/Dy) limit its wider applications. Investigations of Ce-doped Nd₂Fe₁₄B have been attempted recently and multi-main-phase (MMP) (Nd,Ce)₂Fe₁₄B provides a promising way for the preparation of high-performance Ce-doped permanent magnets even though the inner mechanism has not been absolutely understood. We synthesized Ce-doped Nd₂Fe₁₄B nanostructures by the chemical method and successfully realized the obvious property enhancement of the MMP sample compared with that of the single-main-phase one. The coercivity of the MMP nanostructures is nearly 4.5 kOe with a remanence ratio of 0.36 before magnetic orientation, which is much larger than that of the SMP sample (1.7 kOe and 0.21), respectively. The property enhancement mechanism of the MMP sample analyzed mainly by first-order reversal curves could be concluded in three aspects: first, the content of α-Fe will be decreased; hence, the difficulty of the magnetic nucleation is increased. Second, the exchange coupling effect between the adjacent magnetic structures will be strengthened significantly. Last, the grain boundary phases with various magnetic features are formed, enhancing the magnetic pinning effect and specially tuning the inner interactions. This work is helpful for the deeper understanding of the property enhancement mechanism in MMP nanomagnets and provides an instructive way for the effective design and preparation of high-performance MMP Ce-doped Nd₂Fe₁₄B nanomagnets.

Magnetic Heterostructures: Interface Control to Optimize Magnetic Property and Multifunctionality

Generally, magnetic heterostructures are obtained by the growth of another component on the surface of seed nanoparticles. The direct electrical and magnetic interactions between the solid-state interfaces would endow the heterostructures with properties beyond the individual components. We have devoted the past few years to magnetic-optical, magnetic-catalytic, and exchange-coupled heterostructures, where the interface effects regulate and optimize the optical, catalytic, and magnetic properties, respectively. In this Spotlight on Applications, we describe our recent progress on magnetic heterostructures. Upon the understanding on the interface control, we then discuss our recent efforts to synthesize core-shell, dimer, and nanocomposite structures, while the regulation of their magnetic, optical, and catalytic properties is addressed in turn. Finally, we give the perspectives of magnetic heterostructures.

Chemical Synthesis of Magnetic Nanoparticles for Permanent Magnet Applications

Permanent magnets are a class of critical materials for information storage, energy storage, and other magneto-electronic applications. Compared with conventional bulk magnets, magnetic nanoparticles (MNPs) show unique size-dependent magnetic properties, which make it possible to control and optimize their magnetic performance for specific applications. The synthesis of MNPs has been intensively explored in recent years. Among different methods developed thus far, chemical synthesis based on solution-phase reactions has attracted much attention owing to its potential to achieve the desired size, morphology, structure, and magnetic controls. This Minireview focuses on the recent chemical syntheses of strongly ferromagnetic MNPs (H_c >10 kOe) of rare-earth metals and FePt intermetallic alloys. It further discusses the potential of enhancing the magnetic performance of MNP composites by assembly of hard and soft MNPs into exchange-coupled nanocomposites. High-performance nanocomposites are key to fabricating super-strong permanent magnets for magnetic, electronic, and energy applications.

Exchange-Coupling Interaction in Zero- and One-Dimensional Sm2Co17/FeCo Core-Shell Nanomagnets

Rare-earth-based core-shell spring nanomagnets have been intensively studied in the permanent magnet industry. However, the inherent agglomeration characteristics of zero-dimensional (0-D) magnetic nanoparticles are an issue in practical fabrication of magnetic nanocomposites due to deterioration in exchange-coupling interactions, resulting in inferior magnetic performance. Here, with an aim to overcome the structural limitations, we report a new type of SmCo/FeCo core-shell nanomagnet with a well-dispersed one-dimensional (1-D) structure prepared by a combination of electrospinning and electroless plating processes. An FeCo layer with a tailored thickness on nanoscale SmCo was produced to achieve a sufficient exchange-coupling effect. The influence of electroless plating time on the microstructure of fibers was discussed, and comparisons were made as a function of the magnet shape. A 1-D SmCo/FeCo spring nanomagnet having a core diameter ranging from 150 to 200 nm and a shell thickness of 15-20 nm showed a potent exchange-coupling effect compared with its 0-D counterpart. This effectively reduced self-aggregation and further showed a remarkable enhancement in (BH)_max (above 45.7%). We think that this novel structure marks a new era in the exchange-spring magnet industry and may overcome the limitations of traditional core-shell nanomagnets.

Synthesis and reaction mechanism of high (BH)max exchange coupled Nd2(Fe,Co)14B/α-Fe nanoparticles by a novel one-pot microwave technique

Nd–Fe–B based magnets, exhibiting the high energy product, synthesized by cost-effective one pot microwave approach.

High energy product chemically synthesized exchange coupled Nd2Fe14B/α-Fe magnetic powders

The excellent hard magnetic properties of Nd₂Fe₁₄B based magnets have an enormous range of technological applications. Exchange-coupled Nd₂Fe₁₄B/α-Fe magnets were chemically synthesized by a microwave assisted combustion process to produce mixed oxides, followed by a reduction diffusion process to form magnetic nano-composite powder. This synthesis technique offers an inexpensive and facile platform to produce exchange coupled hard magnets. The size dependent magnetic properties were investigated. The formation mechanisms of the oxide powders and the reduction diffusion mechanism were identified. The microwave power was found to play a crucial role in determining the crystallite size. The coercivity of the powder increased with increasing particle size. Room temperature coercivity (H_c) values greater than 9 kOe and magnetization of 110 emu g^-1 was obtained in particles with a mean size of ∼62 nm. An energy product of 5.2 MGOe was obtained, which is the highest reported value for chemically synthesized hard magnetic Nd₂Fe₁₄B/α-Fe powders.

Controlled synthesis and magnetic properties of iron-cobalt-phosphide nanorods

A simple one-step solution-phase synthesis of iron-cobalt-phosphide ((Fe1-xCox)2P) nanorods (NRs) is reported in this paper. Through the control of the amount of Co in the samples, the crystal structure of (Fe1-xCox)2P NRs changes from a pure Fe-rich hexagonal Fe2P type structure to a mixture of Fe-rich hexagonal Fe2P and Co-rich orthorhombic Co2P type structures. These samples show superparamagnetic behavior at room temperature and ferromagnetic properties at 10 K. When the Co composition is 0.09, the (Fe0.91Co0.09)2P sample has the highest coercivity around 5.74 kOe at 10 K. The current route provides a new and general chemical method for tunable preparation of (Fe1-xCox)2P (x < 0.28) NRs, which are significant for the development of new iron- or cobalt-rich permanent magnet materials without rare-earth or noble metals.

Chemical synthesis of Nd2Fe14B hard phase magnetic nanoparticles with an enhanced coercivity value: effect of CaH2 amount on the magnetic properties

Nd₂Fe₁₄B hard phase magnetic nanoparticles were successfully synthesized using a chemical synthesis route followed by a reduction and diffusion process without consuming a large amount of energy.