A general strategy for synthesizing high-coercivity L10-FePt nanoparticles

Operating interfaces to synthesize L10-FePt@Bi-rich nanoparticles by modifying the heating process

A facile strategy to operate interfaces when synthesizing L1₀-FePt@Bi-rich nanoparticles (NPs) has been proposed. Two interfaces are indispensable to obtain the high ordering L1₀-FePt structure. One is the mismatched interfaces between the initial γ-PtBi₂ nuclei and the disordered fcc-FePt phase. The other is the in situ grown coherent interfaces between the L1₀-FePt and Bi-rich phases. Increasing the heating rates when the temperature rises from 120 °C to 310 °C benefits the formation of mismatched interfaces and improves the uniformity of phases and composition in NPs. Reducing the heating rate at higher temperature ensures sufficient time for Bi to diffuse across the coherent interface, which facilitates the disorder-order transition of L1₀-FePt NPs. This study provides a new perspective on operating interfaces during the wet-chemical synthesis process.

Effect of Ag evolution process on ordering transition for L10-FePt nanoparticles synthesized by Ag addition

As a typical element, Ag can effectively promote the ordering transition in the direct synthesis of L10-FePt nanoparticles (NPs). However, the role of Ag in the ordering process and the...

A unique synthesis of rare-earth-Co-based single crystal particles by "self-aligned" Co nano-arrays

In this study, anisotropic SmCo₅ magnets were prepared by a distinctive method, which is the high-temperature reductive annealing of Co@Sm₂O₃ with a specially designed nanostructure. High resolution transmission electron microscopy and elemental mapping show that the precursor self-assembly is composed of hcp-structured Co nano-rods with a coherent crystallographic orientation. During high temperature reduction, the Sm₂O₃ shell preserves the original morphology and alignment of these anisotropic Co nano-arrays, providing a template for hcp-structured SmCo₅ single crystal particle synthesis. The as-prepared SmCo₅ magnets exhibit well-controlled size and morphology, and a high coercivity of 30.9 kOe at room temperature. No stabilizer coating is necessary to prevent the formation of polycrystals in this synthesis.

Eutectic crystallized FePd nanoparticles for liquid metal magnet

Magnetically hard nanoparticles have been widely explored in colloidal solution synthesis, while a high temperature-induced phase transformation is indispensable to achieve its high magnetocrystalline anisotropy. However, a long-standing challenge of magnetic nanoparticles is the inaccessibility of size-controlled growth without sintering-induced agglomeration. Here, we report a universal one-pot eutectic reaction scheme of magnetically hard FePd nanoparticles, in which the crystallization conditions are critical for its magnetic performance. We demonstrate that the stoichiometry between transition metal and eutectic salt and sintering temperature can play an important role in the magnetic coercivity of FePd nanoparticles. In addition, gallium liquid metal is employed as the conductivity filler for the formation of a magnetorheological fluid after mixing with metallic FePd nanoparticles. The liquid composite shows a high metallic and thermal conductivity as an unconventional cooling metallic ferrofluid conductor, and we further demonstrate its potential application in sensors, conductors and thermal interfaces.

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.

Dispersible and manipulable magnetic L10-FePt nanoparticles

Oriented single-domain magnetic nanoparticles with a high remanence ratio M_r/M_s and maximum magnetic energy product (BH)_max have attracted immense attention. However, nanoparticles easily agglomerate due to their extremely small size, which impedes the process of orientation. So manipulating the orientation of nanoparticles is still a key challenge. Here, L1₀-FePt single-domain nanoparticles were successfully synthesized by a chemical method in the liquid phase and nanoparticle-based anisotropic nanocomposites were obtained by dispersing the nanoparticles in liquid epoxy resin under an external magnetic field. The main factors that impact the orientation of L1₀-FePt single-domain nanoparticles were investigated further. It is found that the dispersibility of nanoparticles has a great impact on the degree of orientation, so do the applied magnetic field and the concentration of nanoparticles. Nanocomposites with homodisperse nanoparticles oriented under a suitable external magnetic field exhibit excellent magnetic performance, such as high coercivity H_c and remanence M_r, which gives the nanocomposites a higher (BH)_max than the isotropic samples. The anisotropic nanocomposites show great potential in multifarious permanent magnet applications and fundamental research.

Temperature-dependent heating efficiency of magnetic nanoparticles for applications in precision nanomedicine

The power released by magnetic nanoparticles submitted to an alternating driving field is temperature dependent owing to the variation of the fundamental magnetic properties. Therefore, the heating efficiency of magnetic nanoparticles for applications in precision nanomedicine (such as magnetic hyperthermia or heat-assisted drug delivery) can be significantly affected by the local instantaneous temperature of the host medium. A rate equation approach is used to determine the hysteretic properties and the power released by magnetite nanoparticles, and the heat transport equation is solved in a simple geometry with boundary conditions appropriate to both in-lab experiments and in vivo applications. Size plays a fundamental role in determining the heating efficiency of magnetic nanoparticles; above a critical size, nanoparticles remain inactive, although they can undergo secondary activation. The experimental conditions for optimal thermal efficiency are expressed by a thermal activity diagram for nanoparticles. In the light of the model's results, features, methods, advantages and dangers of magnetic-particle assisted precision nanomedicine ought to be reconsidered. In vivo antitumor applications should take into account the hazards arising from the heat generated by magnetic nanoparticles that diffuse into the neighboring healthy tissue.

Facile liquid-assisted one-step sintering synthesis of superfine L10-FePt nanoparticles

A liquid-assisted one-step sintering method was proposed for the synthesis of L1₀-FePt superfine nanoparticles. The liquid assisted Fe and Pt precursors were homogeneously deposited on NaCl media, which facilitated the nucleation rates, obviously reduced the particle size and promoted the orderly transformation. Through optimizing the sintering parameters, superfine L1₀-FePt nanoparticles (about 7 nm, TEM) with coercivity as high as 2.29 T were obtained. This research highlights the feasibility of synthesizing L1₀-FePt nanoparticles with superfine sizes and ultra-high coercivity.

A liquid-assisted one-step sintering method was proposed for the synthesis of L1₀-FePt superfine nanoparticles.

Chemically synthesized anisotropic SmCo5 nanomagnets with a large energy product

In this communication, we report a facile strategy to chemically synthesize anisotropic SmCo₅ nanomagnets with a large magnetic energy product (BH). First, we designed a Co₃O₄@Sm₂O₃-CaO precursor by a one-pot method, which could be further reduced into uniform single-crystal SmCo₅ particles under the stabilization of CaO coating. Following that, CaO was removed under an oxygen-free environment to impede oxidation. Finally, 130 ± 10 nm SmCo₅ particles were aligned to be nanomagnet, exhibiting a large (BH)_max value of 18.1 MGOe, which is the highest value reported by chemical methods.

Eutectic melt crystallization of L10-FePt

Herein, we report the eutectic growth control of ordered L10-FePt, which directs the nucleation, growth and crystallization of FePt sheets in a single-step reaction. The nature of eutectic crystallization at the eutectic point suggests its role as a high-temperature solvent, exhibiting an advantage in the scale-up production of metastable alloys.