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We report magnetic properties and microstructure of high energy-product MnBi bulk magnets fabricated by low-temperature ball-milling and warm compaction technique. A maximum energy product (BH)max of 8.4 MGOe and a coercivity of 6.2 kOe were obtained in the bulk MnBi magnet at room temperature. Magnetic characterization at elevated temperatures showed an increase in coercivity to 16.2 kOe while (BH) max value decreased to 6.8 MGOe at 400 K. Microstructure characterization revealed that the bulk magnets consist of oriented uniform nanoscale grains with average size about 50 nm. [ABSTRACT FROM AUTHOR]

Nd2Fe14B/α-Fe-based hard/soft nanocomposite magnets with Co addition have been prepared by ball-milling and warm compaction. It was found that Co addition into the magnetically hard phase improves magnetic properties significantly, especially the remanence ratio and coercivity. The effect on the magnetic properties of the selective Co addition may be attributed to enhanced interdiffusion across the hard/soft interface that improves the interface conditions for effective interphase exchange coupling. By optimizing the Co content in the Nd15Fe79-xCoxB6 hard phase, an energy product value about 21MGOe can be obtained in the isotropic Nd2(FeCo)14B/α-(FeCo) nanocomposite magnets compared with 15MGOe of Nd2Fe14B/α-Fe nanocomposite magnets prepared under the same conditions with the same grain size and microstructure, owing to the strengthened intergranular exchange interactions. [ABSTRACT FROM AUTHOR]

This paper reviews recent developments in research in nanostructured permanent magnets (hard magnetic materials) with emphasis on bottom-up approaches to fabrication of hard/soft nanocomposite bulk magnets. Theoretical and experimental findings on the effects of soft phase and interface conditions on interphase exchange interactions are given. Synthesis techniques for hard magnetic nanoparticles, including chemical solution methods, surfactant-assisted ball milling and other physical deposition methods are reviewed. Processing and magnetic properties of warm compacted and plastically deformed bulk magnets with nanocrystalline morphology are discussed. Prospects of producing bulk anisotropic hard/soft nanocomposite magnets are presented. [ABSTRACT FROM AUTHOR]

We report a facile synthesis of ferromagnetic SmCo nanoparticles (NPs) viaa controlled reduction of SmCo–O NPs. The SmCo–O NPs were prepared by co-precipitation of Co(ii) and Sm(iii) acetates with hexadecyl-trimethylammonium hydroxide and were embedded in a CaO matrix. The 7 nm SmCo3.6–O NPs were reduced by Ca at 960 °C and converted into ferromagnetic 6 nm SmCo5NPs with their coercivities reaching 7.2 kOe. The synthesis provides a viable route to ferromagnetic SmCo NPs with controlled compositions and magnetism for high performance permanent magnetic applications. [ABSTRACT FROM AUTHOR]

Monodisperse face-centred tetragonal (fct) FePt nanoparticles with high magnetic anisotropy and, therefore, high coercivity have been prepared via a new heat treatment route. The as-synthesized face-centred cubic FePt nanoparticles were mixed with salt powders and annealed at 700°C. The salts were then removed from the particles by washing the samples in water. Monodisperse fct FePt particles were recovered with the particle size and shape being retained. Coercivity of the isolated particles up to 30 kOe at room temperature has been obtained. [ABSTRACT FROM AUTHOR]

An exchange-coupled FePt/Fe3Pt nanocomposite system with well defined hard/soft two-phase morphology was prepared by reducing chemically synthesized FePt/Fe3O4 bimagnetic nanoparticles. It was interesting to observe that the recoil loop openness is strongly dependent on the sweep rate of applied fields. A quantitative analysis shows a linear relation between the openness of recoil loops and the reciprocal activation volume, indicating that the recoil loops are intimately related to thermal fluctuation. The large open area of the recoil loops for nanocomposite magnets compared to that of single phase magnets is attributed to the unstable magnetic moments in the soft phase. [ABSTRACT FROM AUTHOR]

Mixed spinel hydrophobic ZnxFe1−xO·Fe2O3(up to x= 0.34) nanoparticles encapsulated in polymeric micelles exhibited increased T2relaxivity and sensitivity of detection over clinically used Feridex®. [ABSTRACT FROM AUTHOR]

FePt nanoparticles have the potential to extend the data density of magnetic recording beyond 1 Tbit/in². The phase transformation from low anisotropy, face-centered cubic to face-centered tetragonal with high anisotropy is essential and complex. The samples measured in this paper were annealed in a mixture with fine ground (<20 μm) NaCI. The switching field distributions and activation volumes of two different sizes of particles are presented, 4 and 15 nm. The samples exhibit complex structural behaviour, demonstrating how difficult it is to obtain uniform nanoparticles. We find that the 4-nm particles reverse coherently whereas the 15 nm do not due to inhomogeneous crystallinity. [ABSTRACT FROM AUTHOR]

Coercivity mechanism of the precipitation-hardened Sm(Co,Fe,Cu,Zr)z high-temperature magnets was found to vary with temperature by measurements of reversible magnetization. The magnetization reversal is mainly controlled by domain-wall pinning when temperature is lower than 800 K, while is mainly dominated by nucleation at higher temperature. It is interesting to find that the anomalous temperature dependence of coercivity Hc(T) near Curie temperature of the 1:5 phase is caused by the fast drop of intergranular exchange coupling. This mechanism can also explain the coercivity behavior that the anomalous Hc(T) tends to disappear with increasing z value. [ABSTRACT FROM AUTHOR]

Presents a study that examined the influence of interparticle spacing on the magnetic properties of iron-platinum nanoparticle assemblies. Analysis of the transmission electron micrograph of the nanoparticles; Determination of the room-temperature coercivity of the nanoparticles; Evaluation of the hysteresis loop of the nanoparticles.

Ferromagnetic FeCo nanocrystals with high coercivity have been synthesized using a reductive decomposition method. The sizes and shapes of the nanocrystals were found to be dependent on reaction parameters such as the surfactant ratio, the precursor concentration and the heating rate. Synthesized nanocrystals have a body-centered cubic crystal structure for both particles and nanowires and the (110) crystalline direction is along the long axis of the nanowires. The coercivity and magnetization of the FeCo nanocrystals are found to be dependent on morphology. Nanowires of Fe60Co40 with saturation magnetization of 92 emu g−1 and coercive force of 1.2 kOe have been obtained in this study. [ABSTRACT FROM AUTHOR]