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• A low melting point eutectic alloy Tb 62.5 Co 37.5 as a grain boundary additive was designed and prepared in accordance with the binary alloy phase diagram. • With the addition of 0.5 wt% Tb 62.5 Co 37.5 powders, the remanence increased from 11.1 to 11.86 kGs owing to the optimization of microstructure of the magnet. • The intrinsic coercivity of the magnet was significantly improved due to the formation of an ideal (Nd, Pr, Tb) 2 Fe 14 B core–shell structure. • The remarkable improvement in the corrosion resistance of the magnet owing to the optimization of the composition of the grain boundary phase. To increase the coercivity and corrosion resistance of Nd–Fe–B sintered magnets in high temperature and highly corrosive environments, low melting point Tb 62.5 Co 37.5 alloy powders were added to the starting magnets through intergranular addition. In this study, the magnetic properties, corrosion resistance, and microstructure of magnets were investigated after adding various contents of Tb 62.5 Co 37.5 powders. The coercivity of the magnet was significantly improved from 18.20 to 27.10 kOe when a small amount of Tb 62.5 Co 37.5 powder was added; also, the remanence first increased and then slightly decreased. The microstructure and composition of the modified magnets were studied; it was found that the significant increase in coercivity and the negligible reduction in remanence is because of the densification, improved grain alignment, uniform and continuous Nd-rich phase distribution, as well as the generation of a (Nd, Pr, Tb) 2 Fe 14 B "core–shell" structure surrounding the main phase grain. Furthermore, the corrosion resistance of the magnets was improved significantly owing to the reduction in the electrochemical potential difference between the Nd 2 Fe 14 B main phase and the Nd-rich phase. [ABSTRACT FROM AUTHOR]

• A low melting point eutectic alloy Ho 69.3 Ni 30.7 as a grain boundary additive was designed. • This paper proposes a high-efficiency green physical method to treat these waste products for reuse. • The regenerated magnets obtained the best magnetic properties and the reflection loss of the regenerated magnet in 2wt% Ho 69.3 Ni 30.7. The Nd-Fe-B regenerated magnets are prepared by adding low melting point Ho 69.3 Ni 30.7 alloy at the grain boundary, and the microstructure, structure and overall performance of the Nd-Fe-B regenerated magnets are studied. The results show that the addition of Ho 69.3 Ni 30.7 alloy to grain boundary can optimize the distribution of grain boundary phase, accompanied by the formation of clear and continuous grain boundary phase, which weakens the exchange coupling effect between the adjacent main phases. Meanwhile, the coercivity of the regenerated magnet increases with the increase of Ho 69.3 Ni 30.7 alloy content. The optimal coercivity (16.35 kOe) was obtained at 2 wt% Ho 69.3 Ni 30.7 additions, and the coercivity increased by 1.24 kOe (8.2%) compared with the initial magnet (15.11 kOe). In addition, with the addition of Ho 69.3 Ni 30.7 alloy, the curie temperature of Nd-Fe-B regenerated magnet increased from 303.2℃ to 305.6℃. The reflection loss of regenerated magnet reached −26.42 dB when the amount of 2 wt% Ho 69.3 Ni 30.7 was added, which greatly improved the absorbing performance of the regenerated magnet. Finally, the secondary utilization of waste Nd-Fe-B magnets was realized. [ABSTRACT FROM AUTHOR]

• Preparation of BaFe 12 O 19 and SmFeO 3 composite by sol–gel method. • Use the henkel diagram, the reciprocal curve of the hysteresis loop and the maximum magnetic energy product to explain the magnetic properties of the BaFe 12 O 19 @SmFeO 3 composite. • The addition of SmFeO 3 moves the microwave absorption frequency of the BaFe 12 O 19 @SmFeO 3 composite to low frequency. • While BaM + SmFeO 3 15% has the best absorbing performance, there are two reflection loss peaks, the maximum reflection loss is −48.5 dB, the bandwidth is 3.4 GHz. In this study, BaFe 12 O 19 (BaM)/SmFeO 3 10%, 15 %, and 20 % were synthesized via the sol–gel method. SmFeO 3 was uniformly attached to the BaM surface in the prepared composite. As the SmFeO 3 content increases, the weak magnetic properties of SmFeO 3 caused a gradual decrease in the saturation magnetization of the composite and a gradual increase in its coercive force. Based on the Henkel diagram, an exchange coupling between the two magnetic phases is observed. Similarly, the high permeability of BaM and the best dielectric properties of SmFeO 3 together improved the microwave absorption performance of the composite. The maximum reflection loss and bandwidth of BaM/15 %SmFeO 3 reached −48.5 dB and 3.4 GHz, respectively. [ABSTRACT FROM AUTHOR]

Through arc smelting and high energy ball milling method to synthesized the powders of La x Nd 2- x Fe 17 ( x =0.0, 0.2, 0.4, 0.6). By x-ray diffraction (XRD), scanning electron microscopy (SEM) and laser particle analyzer (LPS) to study the structural, morphology, particle size distribution of the powders, respectively. The electromagnetic parameters and saturation magnetization of the powers were measured by a vector network analyzer (VNA) and vibrating sample magnetometer (VSM), respectively. The saturation magnetization decreases with the La increasing. The minimum absorption peak frequency shifts towards a lower frequency region with an increase of La concentration. The microwave absorbing properties of the composite with different ratios of La 0.2 Nd 1.8 Fe 17 /Ni were studied. The microwave absorbing peaks of the composite shift to higher frequencies, and the microwave absorbing properties improved with the Ni content increase to 20%. The minimum reflection loss is −32.5 dB at 9.8 GHz and the bandwidth less than −10 dB (Microwave absorption rate 90%) reaches 3 GHz with a thickness of 1.8 mm. [ABSTRACT FROM AUTHOR]

• PrFeO 3 ceramics were prepared by the solid-state reaction method and the sol–gel method. • The magnetic properties of PrFeO 3 ceramic have obviously changed from antiferromagnetic to ferromagnetic by increasing the annealing temperature and time. • Possible mechanisms of structure, magnetic and microwave absorption properties have been analyzed. To investigate the magnetic and microwave absorption properties of PrFeO 3 ceramic, the traditional solid-state reaction and sol–gel methods were used. The results show that only an orthorhombic crystal structure was detected by X-ray diffraction and transmission electron microscopy. Interestingly, heat treatment can greatly improve the coercivity of PrFeO 3 ceramic and thus change the magnetic properties from antiferromagnetic to ferromagnetic. The high correlation between the magnetization parameters and bonding characteristics indicated that signifificant contracting of the Fe3+ O c 2− bonds and decrease in Fe3+ O d 2− Fe3+ linkage angles were the main origins of the strong ferromagnetism in the PrFeO 3 ceramic. The PrFeO 3 sample prepared by sol–gel method has good reflection loss. When the simulated thickness is 2 mm, the reflection loss reaches −36.87 dB at 15.92 GHz. The preparation process of the sol–gel method is simple and can be used to synthesize single phase at low temperature, but it is only suitable for the synthesis and performance testing of single phase. The solid-state reation method can be used to determine the phase relationship and phase properties, but it requires high temperature and long annealing time. The experimental results show that the sol–gel method is more suitable for the study of material properties. These results demonstrate the potential application of PrFeO 3 ceramics in magnetic materials and microwave absorbing field. [ABSTRACT FROM AUTHOR]

• The Bi 1–x Ca x FeO 3 (x = 0.0, 0.05, 0.10, 0.15) nanopowders were prepared by sol–gel method. • Study its performance changes by analyzing the unit cell parameters, bond length, bond angle and valence. • The possible mechanism of improving magnetic properties and microwave absorption properties via calcium doping bismuth ferrite was analyzed. Bi 1- x Ca x FeO 3 (x = 0.0, 0.05, 0.1, 0.15) nanopowders were prepared using the sol–gel self-diffusion combustion technology. The effects of structure and grain size changes during the substitution of Bi ions by Ca ions on the magnetic properties and wave absorbing properties of BCFO are discussed. Single-phase BiFeO 3 is a typical rhombohedral R 3 c structure. When the doping amount reaches 0.15, the Ca2+ induced BCFO structure gradually changes to the Pm -3 m phase. The small-sized alkaline earth metal ions Ca2+ (0.99 Å) can successfully replace the A-site Bi3+ ions in BiFeO 3. Ca2+ doping improves the BFO spin helical modulation structure and change the Fe-O-Fe bond angle, thus enhancing the magnetic properties of BCFO. When the doping amount of Ca2+ is 0.10 and the simulated thickness is 2 mm, the best absorption performance at 10.23 GHz is −36.91 dB, and its effective bandwidth reaches 2.81 GHz, which has a good broadband effect. This study provides a reliable candidate material for the synthesis of electromagnetically attenuating ceramic materials with excellent properties. [ABSTRACT FROM AUTHOR]

• Pure phase bismuth ferrite was prepared by sol–gel method. • Pr doping improves the magnetic properties and microwave absorption properties of bismuth ferrite. • Possible mechanisms of structure, magnetic and microwave absorption properties have been analyzed. Bi 1-x Pr x FeO 3 material with perovskite structure was prepared using organic tartaric acid-assisted sol–gel self-propagating combustion method to obtain high-efficiency microwave absorption materials. The influence of the introduction of Pr on dielectric properties and permeability was further studied. After 15% Pr introduced, the lowest reflection absorption loss reaches –32.34 dB, but the absorption bandwidth is only 2.25 GHz. When Pr is 5%, the lowest reflection absorption loss value of −27.31 dB is obtained, and the effective bandwidth which below −10 dB is 3.41 GHz. The structural changes in the process of Pr replacing Bi were analyzed to explore the properties of BPFO perovskite. The influence of strong interaction force, residual magnetization, and natural resonance of ceramic nanoparticles on microwave absorption performance was explored. This work supplies a reliable candidate material for making up electromagnetic attenuation ceramic materials with excellent properties. [ABSTRACT FROM AUTHOR]

• Pure phase barium ferrite was prepared by sol–gel method. • Nd doping improves the magnetic properties and microwave absorption properties of barium ferrite. • Study its performance changes by analyzing the unit cell parameters, bond length, bond angle and valence. Barium ferrite (BaFe 12 O 19) is a multiferroic material with many excellent properties and is easily available. It has good magnetic performance and microwave absorption performance, but it only has the maximum transmission loss in the high-frequency range. To improve its performance, the method of doping is used to improve. The Ba 1-x Nd x Fe 12 O 19 (0 ≤ x ≤ 0.15) was prepared by the sol–gel method. Through the XRD, SEM, VSM, and VNA to characterized the structure and performance of the samples. The results show that Nd ions replace Ba in barium ferrite, and no second phase appears. Along with the doping content increases, the particle size gradually decreases. There is the maximum saturation magnetization and coercive force when x = 0.10. It is attributed to the magnetic Nd ion replacing Ba2+, the magnetic moment increases cause the saturation magnetization increases, the change of Fe3+ and Fe2+ led to the magnetocrystalline anisotropy and the coercive force are increases. When x = 0.10, the complex permittivity increases, the microwave absorption characteristics become well which the maximum reflection loss reaches −34.4 dB, and the bandwidth increases to 4.69 GHz. It can be used in a wider range of fields. [ABSTRACT FROM AUTHOR]