The optimization of microstructure represents a significant methodology for enhancing coercivity(Hcj).This paper concentrates on optimizing the microstructure of magnets through the manipulation of the composition of ...The optimization of microstructure represents a significant methodology for enhancing coercivity(Hcj).This paper concentrates on optimizing the microstructure of magnets through the manipulation of the composition of low-melting-point and high-melting-point elements,thereby achieving the objective of augmenting the comprehensive magnetic properties of magnets.The present study is concerned with the microstructure of magnets comprising three distinct Ga and B contents,and the associated changes in their magnetic properties.The findings indicate that when the Ga content is 0.5 wt%and the B content is 0.88 wt%,the coercivity of the magnets is markedly enhanced.This is evidenced by an increase in coercivity from 8.51 to 14.83 kOe,representing a 74.26%rise.Concurrently,the residual magnetization strength of the magnet remains unaltered.This finding provides a crucial foundation for optimizing the overall magnetic properties of the magnets.The microstructural analysis indicates that a reduction in B content coupled with an increase in Ga content leads to the melting of sharp angles on the surface of the main-phase grains,facilitated by low-melting-point rare-earth-rich phases.This process results in the migration of Fe from the grain boundaries(GBs)to the triple junction phases(TJPs),while Nd migrates from the TJPs to the GBs.This migration results in a reduction in the agglomeration of rare-earth-rich elements within the TJPs,thereby increasing the Nd content in the GBs.This increase enhances the wettability of the GBs,while the reduction of Fe content in this phase mitigates the exchange-coupling effect between the main-phase GBs.Consequently,the GBs become more smooth,more homogeneous and more continuous,which ultimately results in an enhancement of the coercivity of the magnets.展开更多
We describes a controllable synthesis procedure for growing a-Ee2O3 and Ee3O4 nanowires. High magnetic hematite a-Fe2O3 nanowires are successfully grown on Fe0.5Ni0.5 alloy substrates via an oxide assisted vapor-solid...We describes a controllable synthesis procedure for growing a-Ee2O3 and Ee3O4 nanowires. High magnetic hematite a-Fe2O3 nanowires are successfully grown on Fe0.5Ni0.5 alloy substrates via an oxide assisted vapor-solid process. Experimental results also indicate that previous immersion of the substrates in a solution of oxalic acid causes the grown nanowires to convert gradually into magnetite （Fe3O4） nanowires. Additionally, the saturated state of Fe3O4 nanowires is achieved as the oxalic acid concentration reaches 0.75 mol/L. The average diameter and length of nanowires expands with an increasing operation temperature and the growth density of nanowires accumulates with an increasing gas flux in the vapor-solid process. The growth mechanism of a-Fe2O3 and Fe3O4 nanowires is also discussed. The results demonstrate that the entire synthesis of nanowires can be completed within 2 h.展开更多
The structure of a-Fe metal magnetic recording particles coated with silane coupling agents have been studied by TEM, FT-IR, EXAFS, Mossbauer. The results show that a close, uniform, firm and ultra thin layer, which i...The structure of a-Fe metal magnetic recording particles coated with silane coupling agents have been studied by TEM, FT-IR, EXAFS, Mossbauer. The results show that a close, uniform, firm and ultra thin layer, which is beneficial to the magnetic and chemical stability, has been formed by the cross-linked chemical bond Si-O-Si. And the organic molecule has chemically bonded to the particle surface, which has greatly affected the surface Fe atom electronic structure. Furthermore, the covalent bond between metal particle surface and organic molecule has obvious effect on the near edge structure of the surface Fe atoms.展开更多
The magnetization reversal process and hysteresis loops in a single crystal α-iron with nonmagnetic particles are simulated in this work based on the Landau-Lifshitz-Gilbert equation. The evolutions of the magnetic d...The magnetization reversal process and hysteresis loops in a single crystal α-iron with nonmagnetic particles are simulated in this work based on the Landau-Lifshitz-Gilbert equation. The evolutions of the magnetic domain morphology are studied, and our analyses show that the magnetization reversal process is affected by the interaction between the moving domain wall and the existing nonmagnetic particles. This interaction strongly depends on the size of the particles, and it is found that particles with a particular size contribute the most to magnetic hardening.展开更多
In this paper,the fracture behaviors and interface stresses of sintered Nd-Fe-B magnets were investigated.It was revealed that cracks propagated along the interfaces of Nd_(2)Fe_(14)B/Nd_(2)Fe_(14)B,Nd_(2)Fe_(14)B/Nd-...In this paper,the fracture behaviors and interface stresses of sintered Nd-Fe-B magnets were investigated.It was revealed that cracks propagated along the interfaces of Nd_(2)Fe_(14)B/Nd_(2)Fe_(14)B,Nd_(2)Fe_(14)B/Nd-rich phases and within Nd-rich phases.The misfits between 2:14:1 and Nd-rich phases were quantitatively determined,reflecting the concentration of interface stresses in magnet.Grain boundaries of magnet were reconstructed by diffusing Tb-containing and Tb-free sources,respectively.The Tb-rich shells at extensive layers of 2:14:1 grains caused lattice distortion,i.e.,internal stresses,resulting in the crack mode changing from intergranular to transgranular in near surfaces of Tb-containing diffused magnets.Therefore,the bending strengths were deteriorated although the coercivities were apparently enhanced.In the case of Tb-free Pr-Cu diffused magnet,the Pr and Cu elements were enriched at grain boundaries,and the misfits between 2:14:1 and Nd-rich phases were declined,lowering interface stresses and strengthening grain boundaries.The mechanical and magnetic properties of Pr-Cu diffused magnet were simultaneously improved.展开更多
The enhancement of coercivity in Nd-Fe-B sintered magnets modified by Pr_(58)Dy_(10)Cu_(32)alloy was investigated through scanning electron microscope(SEM)and in-situ magneto-optic Kerr effect(MOKE)microscopy.The modi...The enhancement of coercivity in Nd-Fe-B sintered magnets modified by Pr_(58)Dy_(10)Cu_(32)alloy was investigated through scanning electron microscope(SEM)and in-situ magneto-optic Kerr effect(MOKE)microscopy.The modification treatment resulted in the formation of a smooth and continuous weakly magnetic grain boundary layer and the(Nd,Pr,Dy)_(2)Fe_(14)B main phase with a high magnetocrystalline anisotropy field,leading to an increased coercivity of 23 kOe.MOKE observations revealed that the dynamic evolution of the maze domain area under an external magnetic field varied significantly between the original and modified magnets.Compared with the original magnets,the modified magnets exhibited a slower decrease in maze domain area during magnetization and a slower increase during reverse magnetization,contributing to the observed coercivity enhancement.展开更多
In this work,the properties and microstructure of sintered Nd-Pr-Fe-Co-Zr-Ga-Cu-B magnet prepared by the single-step annealing,double-step annealing,and triple-step annealing processes were studied.The triple-step ann...In this work,the properties and microstructure of sintered Nd-Pr-Fe-Co-Zr-Ga-Cu-B magnet prepared by the single-step annealing,double-step annealing,and triple-step annealing processes were studied.The triple-step annealed magnet exhibits the highest intrinsic coercivity of 19.72 kOe,which is a 58.5%enhancement relative to the as-sintered magnet,and has the best temperature stability of coercivity.The best continuity of grain boundary(GB)phase and the highest content of RE6Fe13Ga phase can be observed in the triple-step annealed magnet,along with relatively small grain size.After triple-step annealing process,the phase separation occurs at the triple-junction(TJ)region of the magnet,which is the Fe-rich phase identified as RE6Fe13Ga and the Fe-poor phase identified as Ia-RE_(2)O_(3).The Ia-RE_(2)O_(3)phase located at the corner of the TJ region can extend between the grains of(Nd,Pr)_(2)Fe_(14)B main phase to form the GB phase with a Fe content of less than 15 at%,thereby enhancing the magnetic isolation effect.The lattice misfit between the Ia-RE_(2)O_(3)phase and the adjacent main phase is less than 5%,which is helpful to reduce defects at the edges of the main phase grains,thus reducing the nucleation of reverse domains.展开更多
基金Project supported by the National Key Research and Development Program of China(2022YFB3503302)the Major Projects in Inner Mongolia Autonomous Region(20212D0035)the High-quality Development Special Funds Program Ministry of Industry Technology(TC220H06G)。
文摘The optimization of microstructure represents a significant methodology for enhancing coercivity(Hcj).This paper concentrates on optimizing the microstructure of magnets through the manipulation of the composition of low-melting-point and high-melting-point elements,thereby achieving the objective of augmenting the comprehensive magnetic properties of magnets.The present study is concerned with the microstructure of magnets comprising three distinct Ga and B contents,and the associated changes in their magnetic properties.The findings indicate that when the Ga content is 0.5 wt%and the B content is 0.88 wt%,the coercivity of the magnets is markedly enhanced.This is evidenced by an increase in coercivity from 8.51 to 14.83 kOe,representing a 74.26%rise.Concurrently,the residual magnetization strength of the magnet remains unaltered.This finding provides a crucial foundation for optimizing the overall magnetic properties of the magnets.The microstructural analysis indicates that a reduction in B content coupled with an increase in Ga content leads to the melting of sharp angles on the surface of the main-phase grains,facilitated by low-melting-point rare-earth-rich phases.This process results in the migration of Fe from the grain boundaries(GBs)to the triple junction phases(TJPs),while Nd migrates from the TJPs to the GBs.This migration results in a reduction in the agglomeration of rare-earth-rich elements within the TJPs,thereby increasing the Nd content in the GBs.This increase enhances the wettability of the GBs,while the reduction of Fe content in this phase mitigates the exchange-coupling effect between the main-phase GBs.Consequently,the GBs become more smooth,more homogeneous and more continuous,which ultimately results in an enhancement of the coercivity of the magnets.
文摘We describes a controllable synthesis procedure for growing a-Ee2O3 and Ee3O4 nanowires. High magnetic hematite a-Fe2O3 nanowires are successfully grown on Fe0.5Ni0.5 alloy substrates via an oxide assisted vapor-solid process. Experimental results also indicate that previous immersion of the substrates in a solution of oxalic acid causes the grown nanowires to convert gradually into magnetite （Fe3O4） nanowires. Additionally, the saturated state of Fe3O4 nanowires is achieved as the oxalic acid concentration reaches 0.75 mol/L. The average diameter and length of nanowires expands with an increasing operation temperature and the growth density of nanowires accumulates with an increasing gas flux in the vapor-solid process. The growth mechanism of a-Fe2O3 and Fe3O4 nanowires is also discussed. The results demonstrate that the entire synthesis of nanowires can be completed within 2 h.
基金The authors gratefully acknowledge the support of the National Natural Science Foundation of China (NO.50071057), and the support of the National Synchrotron Radiation Laboratory and Center Foundation (Hefei), China.
文摘The structure of a-Fe metal magnetic recording particles coated with silane coupling agents have been studied by TEM, FT-IR, EXAFS, Mossbauer. The results show that a close, uniform, firm and ultra thin layer, which is beneficial to the magnetic and chemical stability, has been formed by the cross-linked chemical bond Si-O-Si. And the organic molecule has chemically bonded to the particle surface, which has greatly affected the surface Fe atom electronic structure. Furthermore, the covalent bond between metal particle surface and organic molecule has obvious effect on the near edge structure of the surface Fe atoms.
文摘The magnetization reversal process and hysteresis loops in a single crystal α-iron with nonmagnetic particles are simulated in this work based on the Landau-Lifshitz-Gilbert equation. The evolutions of the magnetic domain morphology are studied, and our analyses show that the magnetization reversal process is affected by the interaction between the moving domain wall and the existing nonmagnetic particles. This interaction strongly depends on the size of the particles, and it is found that particles with a particular size contribute the most to magnetic hardening.
基金supported by the National Natural Science Foundation of China(No.52271165)the National Key R&D Program of China(No.2022YFB3505501).
文摘In this paper,the fracture behaviors and interface stresses of sintered Nd-Fe-B magnets were investigated.It was revealed that cracks propagated along the interfaces of Nd_(2)Fe_(14)B/Nd_(2)Fe_(14)B,Nd_(2)Fe_(14)B/Nd-rich phases and within Nd-rich phases.The misfits between 2:14:1 and Nd-rich phases were quantitatively determined,reflecting the concentration of interface stresses in magnet.Grain boundaries of magnet were reconstructed by diffusing Tb-containing and Tb-free sources,respectively.The Tb-rich shells at extensive layers of 2:14:1 grains caused lattice distortion,i.e.,internal stresses,resulting in the crack mode changing from intergranular to transgranular in near surfaces of Tb-containing diffused magnets.Therefore,the bending strengths were deteriorated although the coercivities were apparently enhanced.In the case of Tb-free Pr-Cu diffused magnet,the Pr and Cu elements were enriched at grain boundaries,and the misfits between 2:14:1 and Nd-rich phases were declined,lowering interface stresses and strengthening grain boundaries.The mechanical and magnetic properties of Pr-Cu diffused magnet were simultaneously improved.
基金supported by the National Key Research and Development Program of China(Grant Nos.2021YFB3500300,2023YFB3507000,and 2023XYJG0001-01-03)the National Natural Science Foundation of China(Grant No.52171167)Inner Mongolia Northern Rare Earth Advanced Materials Technology Innovation Co.,Ltd.Project(Grant No.CXZX-B-202304-0004).
文摘The enhancement of coercivity in Nd-Fe-B sintered magnets modified by Pr_(58)Dy_(10)Cu_(32)alloy was investigated through scanning electron microscope(SEM)and in-situ magneto-optic Kerr effect(MOKE)microscopy.The modification treatment resulted in the formation of a smooth and continuous weakly magnetic grain boundary layer and the(Nd,Pr,Dy)_(2)Fe_(14)B main phase with a high magnetocrystalline anisotropy field,leading to an increased coercivity of 23 kOe.MOKE observations revealed that the dynamic evolution of the maze domain area under an external magnetic field varied significantly between the original and modified magnets.Compared with the original magnets,the modified magnets exhibited a slower decrease in maze domain area during magnetization and a slower increase during reverse magnetization,contributing to the observed coercivity enhancement.
基金Project supported by the Major Special Project of Fujian Province(2023HZ021005)the Guiding Project of Fujian Province(2023H0006)+2 种基金the Major Project of Science and Technology of Fuzhou(2022-ZD-010)the Young and Middle-aged Teachers Education Scientific Research Project of Fujian Province(JAT200594,JAT231008)the Natural Science Foundation of Fujian Province(2022J011151)。
文摘In this work,the properties and microstructure of sintered Nd-Pr-Fe-Co-Zr-Ga-Cu-B magnet prepared by the single-step annealing,double-step annealing,and triple-step annealing processes were studied.The triple-step annealed magnet exhibits the highest intrinsic coercivity of 19.72 kOe,which is a 58.5%enhancement relative to the as-sintered magnet,and has the best temperature stability of coercivity.The best continuity of grain boundary(GB)phase and the highest content of RE6Fe13Ga phase can be observed in the triple-step annealed magnet,along with relatively small grain size.After triple-step annealing process,the phase separation occurs at the triple-junction(TJ)region of the magnet,which is the Fe-rich phase identified as RE6Fe13Ga and the Fe-poor phase identified as Ia-RE_(2)O_(3).The Ia-RE_(2)O_(3)phase located at the corner of the TJ region can extend between the grains of(Nd,Pr)_(2)Fe_(14)B main phase to form the GB phase with a Fe content of less than 15 at%,thereby enhancing the magnetic isolation effect.The lattice misfit between the Ia-RE_(2)O_(3)phase and the adjacent main phase is less than 5%,which is helpful to reduce defects at the edges of the main phase grains,thus reducing the nucleation of reverse domains.
