Micron-scale 1:5H-based precipitated phase with the lamellar structure of sintered Sm_(2)Co_(17)-based magnets and its potential application

The excellent thermal stability of magnetic properties of Sm_(2)Co_(17)-based magnets is their most impor-tant feature.However,this stability is reduced when the maximum energy product of Sm_(2)Co_(17)-based magnets is improved,which is mainly determined by the Fe/Cu distribution of the 2:17R cell and 1:5H cell boundary phases.During the demagnetization process,the Cu-rich 1:5H cell boundary phase with a width of 2-15 nm obstructs the motion of the domain walls,yielding coercivity.Herein,we report a micron-scale Cu/Zr-rich and Fe-lean 1:5H-based precipitated phase with a lamellar structure,probably induced by Sm_(2)O_(3) doping.This structure enables the separate regulation of Fe and Cu distribution for Sm_(2)Co_(17)-based magnets with Fe-rich 2:17R cell phases and Cu-rich 1:5H cell boundary phases,consid-erably optimizing the thermal stability of magnetic properties.This discovery can be further developed to produce Sm_(2)Co_(17)-based magnets with high performance and excellent thermal stability of magnetic properties.

Optimization of microstructures and magnetic properties of Sm(Co_(bal)Fe_(0.227)Cu_(0.07)Zr_(0.023))_(7.6) magnets by sintering treatment

Magnetic properties and microstructures of Sm(Co_(bal)Fe_(0.227)Cu_(0.07)Zr_(0.023_)_(7.6) sintered magnets were optimized by sintering treatment. Results show that the knee-point magnetic field, Hknee, is twofold up and the intrinsic coercivity Hcjincreases by 40%, ranging from 21.64 to 30.39 kOe at the cost of a little decrease of Brfrom 10.84 to 10.31 kGs with sintering temperature decreasing from 1488 to 1473 K. And the average domain width is narrower and more uniform for the specimen sintered at 1473 K than that of the specimen sintered at 1488 K. It is impressive that the density of lamellar phase increases from ~0.050 to ~0.058 nm^(-1) with the sintering temperature decreasing from 1488 to 1473 K. Moreover, the average cellular size is about ~84 nm for the magnets sintered at 1473 K, which is 80% of that of the magnets sintered at 1488 K(~97 nm). And the cell boundary width of the magnets sintered at 1473 K(~7 nm) is only half average width of the magnets sintered at 1488 K(~14 nm). It is found that the Cu content in the cell boundaries is much higher(~17 at%) in the magnets sintered at 1473 K compared to that of the magnets sintered at 1488 K(~10 at%). It can be concluded that smaller cells and narrower cell boundaries together with higher gradient of Cu content are key points for obtaining the optimum Hkneeand Hcj.

The microstructure and magnetization reversal behavior of melt-spun (Nd_(1-x)Ce_x)-Fe-B ribbons

In this study, the alloy ingots with nominal compositions of （Nd1_xCex）31FebalCoo.2Gao.1B （x = 0, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%） were prepared and then melt-spun to form nanocrystalline ribbons at the wheel speed of 20 m/s. XRD results show that all melt-spun ribbons exhibit the tetragonal structure （Nd,Ce）2Fe14B phase with the space group P42]rnmm. The Curie temperature and lattice constant decrease with the increase of Ce content. The Curie temperature decreases gradually from 306 to 247 ~C with the increase of Ce content. Those results indicate that Ce element has been incorporated into Nd2Fe14B main crystalline phase and formed （Ce,Nd）-Fe-B hard magnetic phase. It is also found that the remanence ratio （Mr/Ms） decreases from 0.693 to 0.663 and the coercivity （Hc） decreases from 18.7 to 14.2 kOe with the increase of Ce content. However, a relatively high coercivity of 18.3 kOe for （Ndl xCex）31FebalCoo.2Gao.lB （x = 0.2） melt-spun ribbon is achieved. The coercivity is sensitive to microstructure. The AFM patterns show the sample （x - 0.2） has the most uniform and finest micro- structure. The magnetization reversal behavior （0M plots） is discussed in detail. The positive 0M value is observed in every sample, which confirms the existence of exchange coupling interaction. Evidently, the OM maximum value reaches 0.9 in the sample （x - 0.2）. It is indicated that the intergranular exchange coupling effect is the strongest, which is consistent with coercivity enhancing.