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To improve the mechanical properties of hot-deformed Nd-Fe-B magnets, anisotropic Nd-Fe-B magnets doped with SiC whiskers were fabricated by hot-pressing and hot-deformation processes. The influence of the SiC whiskers on the microstructure and magnetic and mechanical properties of the Nd-Fe-B magnets was investigated. The bending strength of the hot-deformed Nd-Fe-B magnets reinforced with SiC whiskers first increased and then decreased with increasing SiC whisker content from 0 wt.% to 1.0 wt.%. The composite magnet with 0.5 wt.% SiC whiskers exhibited the highest average bending strength and still retained the maximum energy product of approximately 45.8 MGOe. The morphology of the fracture surface of the magnets revealed that the majority of the SiC whiskers were distributed at intergranular boundaries. The phenomenon of SiC whisker pullout from the matrix was observed, which results in increased bending strength. The improvement of the mechanical properties can be attributed to the high strength of the SiC whiskers, the whisker pullout phenomenon, and crack deflection. [ABSTRACT FROM AUTHOR]

To apply bulk hot-deformed magnets into commercial fields, it is quite necessary to deeply understand the origins and evolution of their inhomogeneous microstructure. In this work, the microstructure of hot-deformed nanocrystalline cylindrical Nd-Fe-B magnets with a dimension of ∼24.8 mm in diameter and ∼7.0 mm in height along the radial direction was investigated in order to correlate them with the inhomogeneous magnetic properties. The remanence was 1.42 T, 1.37 T, and 1.30 T for the samples taken from the center (sample P3), subcenter (sample P2), and edge (sample P1) of the hot-deformed magnet, respectively. Scanning electron microscopy images showed from the P3 to P1 the interval of strip-shaped Nd-rich layers increased. Meanwhile, the perpendicularity between the pressure direction and the Nd-rich layers deteriorated for the samples from the P3 to P1. Well oriented platelet-shaped grains with c-axis parallel to the pressure direction were observed in the P3 sample, and the orientation gradually deteriorated with the position changing from the center to the edge. It was also found that large Nd-rich phase aggregation areas occurred in the edge sample. The maximum value of Henkel plot decreased gradually for the samples from the P3 to P1, which was caused by the thickened grain boundary observed by transmission electron microscopy. The openness of recoil loops increased gradually from the center to the edge due to the aggregation of the Nd-rich phase. The inhomogeneous microstructure shows distinct effects on magnetic properties, therefore changing the magnetization behavior along the radial direction of hot-deformed magnets. • The microstructure of the hot-deformed magnet along radial direction is inhomogeneous. • The inhomogeneous microstructure partly results from the original powder status. • Uneven temperature and effective strain lead to the inhomogeneous microstructure. • Magnetization behavior is changed by the inhomogeneous microstructure. [ABSTRACT FROM AUTHOR]

Nd-Fe-B composite magnets with different amounts of \CaF2 have been prepared by sintering at different temperatures. The microstructure and densities of the Nd-Fe-B composite magnets were investigated by scanning electron microscope and Archimedes method. The electrical and magnetic properties were measured with a four probe electrical resistivity meter and a NIM-2000HF hysteresisgraph meter. The results show that \CaF2 was distributed in the grain boundary. The electrical resistances of the composite magnets increased with the increase of the amounts of \CaF2, while the magnetic properties of the magnets deteriorated markedly. The electrical resistances of the Nd-Fe-B composite magnets with 3, 6 and 9 wt.% as-bought \CaF2 sintered at 1050 ^\circ\C were 270, 320 and 400~\mu\Omega ~\cm, which increased approximately 17%, 39% and 74% over that of the magnet without \CaF2 (230~\mu\Omega~\cm). The maximum energy products, \(BH)\max, of the composite magnets with 3, 6 and 9 wt.% as-bought \CaF2 sintered at 1050 ^\circ\C were 41.03, 35.77 and 28.66 MGOe, respectively. The densities of the composite magnets decreased with the increase of the amounts of \CaF2. High energy ball milling can refine \CaF2 to nanoscale and thus improve its distribution in the composite magnets. The \(BH)\max of the Nd-Fe-B magnets with 3 wt% \CaF2 first increased and then decreased with the increase of milling time. But the electrical resistivities of the sintered Nd-Fe-B magnets with the \CaF2 without milling and after high energy ball milling have little change. [ABSTRACT FROM PUBLISHER]

The coercivity of the die-upset Nd–Fe–B magnets was enhanced remarkably by the Nd–Cu eutectic alloy addition. The initial magnetization curves show that the magnetization reversal transforms from the nucleation fields for an Nd–Cu free magnet to the coexistence of the nucleation and domain-wall pinning fields for the magnet with Nd–Cu addition. The transmission electron microscopy images reveal that more triple-junction regions, which are enriched with Nd and Cu elements, distribute in the die-upset magnets with Nd–Cu addition. These regions become the domain-wall pinning center and enhance the coercivity of the magnets. Moreover, the thickness of the grain boundary phase increases with the Nd–Cu addition, which declines the coupling between the Nd–Fe–B grains and then further improves the coercivity. [ABSTRACT FROM AUTHOR]

The Sm2Co17 magnet is the most promising candidate for high temperature applications. The microstructure evolutions and losses in the magnetic properties of the magnet in high temperature aging status have been investigated. The Sm(CobalFe0.22Cu0.068Zr0.025)7.75 magnets were prepared using the conventional powder sintering method. The magnet samples were isothermally aged at 500°C, 600 °C, and 700 °C for 72 h, respectively. The magnetic properties and the demagnetization curve were kept invariable for the magnet samples aged at 500 °C. The coercivity Hcj of the magnet samples decreased with increasing aging temperature. The Hcj decreased from 29.2 kOe for the original status samples to 10.8 kOe for the samples aged at 700 °C. The cell structure in the magnet is not destroyed after aging at 700 °C for 72 h. The deterioration of the magnetic properties and the demagnetization-curve squareness was caused by an increasing lattice mismatch between the 2:17R cell phase and the cell-boundary 1:5H phase, and by an increasing cell diameter for the magnet sample aged at a high temperature. [ABSTRACT FROM AUTHOR]

Abstract: Based on first-principles spin-density functional calculations, we investigate the electronic and magnetic properties of Mn-doped GaN nanotubes in which two of Ga atoms are substituted by Mn atoms. Similar to the case of Mn in bulk GaN, our calculations show that Mn atoms also act as an acceptor and all of the ground states for the Mn-doped GaNNTs are ferromagnetic. Moreover, the ferromagnetism is isotropic and independent of the chirality and diameter of the nanotubes. It is found that the most favorable configuration is the first-nearest neighbor Mn model, which is mainly mediated by both the hole–hole interaction and the dipole–dipole interaction. [Copyright &y& Elsevier]

The paper studies the phase transition of ingot with the composition (Ce 50 Nd 50 ) 30 Fe bal Co 4 Ga 0.2 B 0.92 after the annealing treatment at 1050 °C. The melt-spun ribbons which is prepared by the two treatment status ingots. The phase structure and microstructure morphologies of the ingots and melt-spun ribbons were analysed and observed by XRD and SEM. It was found that the grain size of the ribbons is on the nanometer scale. The EDS results show that there are four different phases in the ingot: (CeNd) 2 Fe 14 B, α-Fe, Ce-rich phase and Nd-rich phase. After the annealing treatment, α-Fe, Ce-rich phase, and Nd-rich phase were obviously reduced and the contents of the main phase was significantly increased in the annealed ingot compared with the unanneal treatment ingot. The VSM results show that there is a peak waist in the ribbon which is prepared by the untreated ingot. Because the ingot is uneven, the ribbons may have the secondary phase, the Hcj is 8394 Oe. But the demagnetization curves of the ribbons, which is prepared by the annealed ingot, is relatively smooth and without the soft magnetic phase and the Hcj is 12,528 Oe, which is higher than the unanneal treatment ingot. We can know that the ingot with fine organization is the key factors to preparing high-performance ribbons. [ABSTRACT FROM AUTHOR]

Precipitation-hardened Sm 2 Co 17 based sintered permanent magnet has been attracting a great deal of attention by virtue of its distinguished high temperature magnetic properties, extremely low temperature coefficient, excellent corrosion resistance and oxidation resistance. Magnetic properties and microstructures of Sm 2 Co 17 based sintered permanent magnets with the nominal composition Sm(Co bal Fe 0.245 Cu 0.07 Zr 0.02 ) 7.8 have been investigated. The magnets referred were prepared using the conventional powder metallurgy method, where the techniques of making powder were ball-milling and jet-milling, respectively. The corresponding magnetic properties of the magnet made of ball-milling powder are the remanence B r =1.157 T (11.57 kGs), the intrinsic coercivity H cj =752 kA/m (9.46 kOe), and the maximum magnetic energy product (BH) max =221 kJ/m 3 (27.8 MGOe), while that of jet-milling powder are B r =1.133 T (11.33 kGs), H cj =2613 kA/m (32.83 kOe), and (BH) max =242 kJ/m 3 (30.4 MGOe). The cause of such a significant difference between the two is considered to be that the actual chemical compositions in micro zone are different, which is deemed to be related to the different actual chemical compositions due to the differences of oxygen content in the final magnets: ~2800 and ~1300 ppm. [ABSTRACT FROM AUTHOR]