The effects of Tb addition on the microstructure and magnetic properties of the NdFeB magnets prepared by HD method were investigated by X-ray diffraction(XRD) and BH magnetometers.The results of the microstructure showed that both the Tb-doped and undoped permanent magnets were composed mostly of Tetragonal phase Nd2Fe14B(space group P42/mnm) and a trace amount of Nd-rich phase.Accordingly,addition of Tb led to a decrease of the pole density factor of(004),(006) and(008) crystal plane of the Nd2Fe14B phase calculated by Horta formula,but the coercivity of the magnets increased from 2038 kA/m up to 2302 kA/m as a consequence of Tb addition.The study of the Hc(T)/Ms(T) versus/Ms(T) behavior showed that the nucleation was the dominating mechanism for the magnetization reversal in both sintered magnets,and the microstructural parameters of αk and Neff were obtained also.The Kronmüller-plot showed an increase of the αk responsible for an increase of the coercivity.
Rapidly solidified nanocrystalline α-Fe/Nd2Fe14B alloys with enhanced coercivity were obtained by melt spinning. The effects of Ti addition on the microstructure and magnetic properties of the nanocomposite α-Fe/Nd2Fe14B alloys were investigated by X-ray diffraction (XRD) and superconducting quantum interference device (SQUID) magnetometer. The analysis of XRD showed that Vα-Fe estimated to be about 35.3% in the Ti-free α-Fe/Nd2Fe14B nanocomposites decreased down to 26.5% as the addition of was 5 at.% Ti. Accordingly, adding Ti resulted in relevant improvements of magnetic properties, especially of the coercivity Hc from 595 kA/m up to 1006 kA/m. The dependence of Mirrev(H)/2Mr on the reverse field H indicated that nucleation was the dominating mechanism for the magnetization reversal in these nanocomposites. The analysis of the temperature dependence of the demagnetization curve in the α-Fe/Nd2Fe14B nanocomposite magnets indicated that a reduction of αex could play a leading role in an increase in the coercivity of Ti-doped sample.
The nanocrystalline magnets with nominal compositions of Sml_xLuxCo6.8Zr0.2 （x-=0, 0.2, 0.4, 0.6） were prepared directly by the intensive milling. The effects of Lu content on the phase structure, the magnetic properties, and magnetization behaviors were also investigated. The XRD patterns of the as-milled samples showed a single SmCo7 phase with TbCu7 structure. Lu addition was proved to result in relevant improvements in the microstructure and magnetic properties, especially in the maximum energy product （BH）max. It was shown that a higher maximum energy product and coercivity of about 17.47 kJ/m3 and 473.45 kA/m were obtained in the sample with x=0.2. From the analysis of the magnetization reversal behavior, it was found that a stronger intergrain exchange coupling interaction was observed in the samples with Lu-doping. From the studies of the coercivity mechanism, it was shown that nucleation model was the dominant magnetization reversal process at the elevated temperature.
