Effect of TbF_(3)diffusion on the demagnetization behavior and domain evolution of sintered Nd-Fe-B magnets by electrophoretic deposition

We studied the magnetic properties and domain evolution of annealed and TbF3-diffused sintered Nd-Fe-B magnets using the electrophoretic deposition method.After TbF_(3)diffusion,the coercivity increased significantly by 9.9 kOe and microstructural analysis suggested that Tb favored the formation of the(Nd,Tb)_(2)Fe_(14)B shell phase in the outer region of the matrix grains.The first magnetization reversal and the dynamic successive domain propagation process were detected with a magneto-optical Kerr microscope.For the TbF_(3)-diffused magnet,the magnetization reversal appeared at a larger applied field and the degree of simultaneous magnetization reversal decreased compared with an annealed magnet.During demagnetization after full magnetization,the occurrence of domain wall motion(DWM)in the reproduced multi-domain regions was observed by the step method.The maximum polarization change resulting from the reproduced DWM was inversely related to the coercivity.The increased coercivity for the diffused magnet was mainly attributed to the more difficult nucleation of the magnetic reversed region owing to the improved magneto-crystalline anisotropy field as a result of Tb diffusion.

Effect of spin-reorientation transition of cell boundary phases on the temperature dependence of magnetization and coercivity in Sm_(2)Co_(17) magnets

Four Sm_(2)Co_(17)magnets with spin-reorientation transition(SRT)of cell boundary phases(CBPs)are prepared by liquid-phase sintering.The temperature of the SRT of CBPs(T_(SR)^(1:5))is regulated from 125 K to 195 K by adding 0 wt.%,3 wt.%,6 wt.%and 9 wt.%Dy_(88)Cu_(12)alloy powder.The effect of SRT of Sm_(2)Co_(17)magnet CBPs on the temperature dependence of the magnetization(M-T)and coercivity(H-T)is systematically investigated.The temperature dependence of the magnetization is influenced by the SRT of CBPs.The M-T curves measured during the heating process are larger than those measured during the cooling process when T<T_(SR)^(1:5).When T=T_(SR)^(1:5)there is a bifurcation point.When T>T_(SR)^(1:5)the M-T curves overlap and the M-T derivation curve shows that the magnetization of the magnet has low temperature dependence of magnetization above T_(SR)^(1:5).With increasing T_(SR)^(1:5),the initial temperature of the low temperature dependence of magnetization shifts towards a higher temperature.The coercivity temperature coefficient becomes positive as the SRT effect increases,and the temperature range of the positive coercivity temperature coefficient moves towards higher temperatures as T_(SR)^(1:5)increases.This reveals that SRT of CBPs has little effect on the temperature dependence of magnetization above T_(SR)^(1:5),while the temperature dependence of coercivity is optimized.The temperature range of magnetization and coercivity with low temperature dependence tends towards higher temperatures,which is conducive to the preparation of magnets with a low temperature coefficient at higher temperatures.