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The structure and magnetic properties of Fe nano-particles prepared by the sonochemistry method were systematically studied. The power of sonicator played an important role in the microstructure and magnetic properties of the nano-particles. Initial X-ray powder diffraction patterns of Fe nano-particles prepared with a power of 180W and 450W exhibited amorphous-like diffraction peaks. TEM images showed that the average particle size of Fe nano-particles made with 180W is 2-3nm and increases to 5-6nm with 450W. The amorphous and superparamagnetic nature of the Fe nano-particles has been confirmed by TEM, SAD and magnetometry measurements. The saturation magnetization (Ms) of the 2-3nm Fe nano-particles is only 0.414T. Increasing the power to 450W, the Ms of Fe nano-particles with the size of 5-6nm can reach the value of 0.958T. To obtain fully crystalline particles, the Fe nano-particles were annealed at 923K for 2min. After annealing, the Ms increased to 1.807T. TEM results show that the amorphous-like Fe nano-particles have been transformed to crystalline bcc α-Fe. [ABSTRACT FROM AUTHOR]

Ternary DyFeB nanoparticles and nanoflakes were prepared by surfactant-aid high-energy ball milling. As the particle size decreases, the coercivity decreases from 16.8 to 0.4 kOe, indicating substantial influence of the size on the coercivity of the particles. In addition, strong magnetic anisotropy was achieved in magnetically aligned DyFeB nanoflakes. [ABSTRACT FROM PUBLISHER]

The structure and magnetic properties were studied for the ternary Tb-Fe-B nanoparticles and nanoflakes prepared by surfactant-aid high energy ball milling and subsequent size-selection. For the nanoparticles, significant room-temperature coercivity up to 10.6 kOe was achieved with the average particle size of 31.4 nm, but it decreases substantially to 400 Oe as the size is down to 8.2 nm. For the nanoflakes, the thickness is in the range of 50-80 nm while the length is about 1.1 μm, and high coercivity of 22.1 kOe and strong magnetic anisotropy were obtained simultaneously, indicating that the nanoflakes possess excellent permanent magnetic properties. [ABSTRACT FROM AUTHOR]

The microstructure and magnetic properties were studied for the sintered Nd–Fe–B permanent magnet doped with terbium (Tb) nanoparticles. Investigation shows that Tb is enriched as Tb2Fe14B and/or (Nd,Tb)2Fe14B phase in the surface region of the Nd2Fe14B matrix grains indicated by the remarkable enhancement in the magnetocrystalline anisotropy field of the magnet. Furthermore, the Tb-rich grain surface region with high crystal anisotropy increases the nucleation field of reverse domains in the demagnetization process. As a result, the magnet doped with a small amount of Tb nanoparticles possesses enhanced coercivity without sacrificing its magnetization. [ABSTRACT FROM AUTHOR]

Nd-Fe-B permanent magnets doped with a small amount of praseodymium (Pr) nanoparticles were prepared by conventional sintering method. Effects of the Pr nanoparticles doping amount and the sintering temperature on the magnetic properties of the magnets were studied. As the doping amount increases, the coercivity of the magnets rises gradually, while the remanence and the maximum energy product of the magnets rise first, peak at 1.0 wt. % of Pr nanoparticles doping, then drop. The optimal sintering temperature was determined as 1040 °C. Under optimal doping amount and sintering temperature, the Nd-Fe-B magnet bears good magnetic properties of Br of 1.386 T, Hci of 1170 kA/m and (BH)max of 371 kJ/m3, which are better than the Pr-free magnet's magnetic properties of Br of 1.358 T, Hci of 1097 kA/m and (BH)max of 354 kJ/m3, suggesting the doping of Pr nanoparticles is a promising way to enhance the magnetic properties of sintered Nd-Fe-B magnets. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties were studied for ternary Tb-Fe-B melt-spun ribbons with nominal composition of Tb14Fe86-xBx (x = 5.2-6.8). Effect of boron content and melt-spun wheel speed on the coercivity of the ribbons was investigated. With the increase of boron content, the coercivity of the Tb-Fe-B ribbons increases first, and then decreases. XRD results show that the impurities of TbFe2 phase and FeB phase exist in low boron content and high boron content ribbons, respectively, resulting in the coercivity degradation of the ribbons. For the Tb14Fe79.6B6.4 ribbons, the wheel speed plays an important role in their magnetic properties. As the wheel speed increases from 5 to 25 m/s, the saturation magnetization and the remanence of the ribbons drop monotonically, while the coercivity increases first, peaks at 77.4 kOe, and then decreases. Further SEM observation indicates that the microstructure of the optimal ribbons was composed of fine and uniform crystal grains, which was responsible for the ultrahigh intrinsic coercivity of the ribbons. [ABSTRACT FROM AUTHOR]