The arrangements of the easy magnetization axis[001]of columnar Nd_(2)Fe_(14)B crystals in the laser scanned layer on anisotropic sintered Nd_(15)Fe_(77)B_(8)magnets were investigated by XRD and the Bitter method.The ...The arrangements of the easy magnetization axis[001]of columnar Nd_(2)Fe_(14)B crystals in the laser scanned layer on anisotropic sintered Nd_(15)Fe_(77)B_(8)magnets were investigated by XRD and the Bitter method.The results show that the common effects of both the heat flux and the substrate magnetization orientation constrain the columnar Nd_(2)Fe_(14)B solidified from the laser melting pool to form the c-axis texture orientated with the same direction as that of the substrate,when the geometric relationship between the heat flux in the laser scanning layer and c-axis texture orientation of the substrate is perpendicular to each other,and if the laser scanning velocity is no less than 25 mm·min^(-1).The c-axes of columnar Nd_(2)Fe_(14)B crystals are no longer randomly distributed in the plane normal to their preferential growing direction as they are randomly done in both ingots cooled by water-cooling copper mould and directionally solidified Nd-Fe-B rods.展开更多
Texture evolution in nanocomposite Nd_2Fe_ 14B/α-Fe magnets prepared by direct melt spinning was investigated. The free surface and wheel-contacted surface exhibit different texture direction. Modification of composi...Texture evolution in nanocomposite Nd_2Fe_ 14B/α-Fe magnets prepared by direct melt spinning was investigated. The free surface and wheel-contacted surface exhibit different texture direction. Modification of composition not only enhances magnetic properties, but also changes texture direction of the ribbon. Low temperature heat treatment can increase the magnetic properties to some extent, and high temperature annealing decreases the magnetic properties. Both low and high temperature heat treatment have effects on grain orientation, but the difference still exists between the two surfaces of the ribbon. So it is infeasibility to prepare anisotropic Nd_2Fe_ 14B/α-Fe nanocomposite magnets by direct melt spinning.展开更多
Based on the observation of temperature variation of both domain structure and magnetic con- trast.the thermal demagnetization and randomness of domain nucleation was discussed.
Microstructure and magnetic properties of Nd8.5Fe77.1B6.4Co4Zr3Nb0.5V0.5 nanocomposite ribbons were investigated. A fine and uniform grain with 30 nm in average size was achieved for the ribbons annealed at 710 ℃ for...Microstructure and magnetic properties of Nd8.5Fe77.1B6.4Co4Zr3Nb0.5V0.5 nanocomposite ribbons were investigated. A fine and uniform grain with 30 nm in average size was achieved for the ribbons annealed at 710 ℃ for 4 min, which enhanced the interaction coupling between grains and improved the magnetic properties. The results of three-dimensional atom probe (3DAP) revealed that V-enriched intergranular phase existed at the grain boundaries, suppressing the grain growth during crystallization process. The remanence and coercivity for annealed ribbons reached to 80 emu·g-1 and 567 kA·m-1, respectively.展开更多
Easy and hard magnetization curves of Nd_2Co_(14)B compound have been measured with extracting-sample-magnetometer(μ_0H_(max)=6T)at 10～300 K.Magnetic anisotropy constants K_1 and K_2 have been determined by fitting ...Easy and hard magnetization curves of Nd_2Co_(14)B compound have been measured with extracting-sample-magnetometer(μ_0H_(max)=6T)at 10～300 K.Magnetic anisotropy constants K_1 and K_2 have been determined by fitting the hard magnetization curves,in which only K_1 ,K_2 and misalignment angle have been taken as fitting parameters.The values of K_1 and K_2 at 4.2 K were derived by extrapolation. Anisotropy coefficients,x_2~° and x_4~°were derived from the anisotropy constants.The anisotropy constant K_2 increases rapidly with increasing temperature when T<T_(sr)and slowly when T>T_(sr).The temperature depen- dence of the magnetic anisotropy coefficient x_2~° was fitted with the formula.The anisotropy coefficients x_2~° can be well described by the tenth-power law from 4.2 K to T_(sr)and by the sixth-power law from T_(sr_ to 300 K.展开更多
A series of magnetic properties of Tm_2Fe_(14)B are explained quantitatively by the calculations based on the single ion model. The magnetic properties include the temperature dependence of the spontaneous magnetizati...A series of magnetic properties of Tm_2Fe_(14)B are explained quantitatively by the calculations based on the single ion model. The magnetic properties include the temperature dependence of the spontaneous magnetization, the spin reorientation temperature and the magnetization curves along the principal crystal axes at 4.2, 100, 150 and 200 K. The values of the exchange field and the crystalline electric field parameters used in the calculations are μ_BH_(ex)(T=0 K)=135, B_2~0=1.77, B_2~2=±2.97, B_4~0=-3.06×10^(-3), B_4^(-2)=0, B_4~4=-6.82×10^(-3), B_6~0=1.05× 10^(-5), B_6^(-2)=±7.40×10^(-5), B_6~4=1.96×10^(-4), and B_6^(-6)=0 all in K unit. The magnetization processes of the Fe-and Tm-sublattices at different temperatures are analysed. The processes are characterized by the non-collinearity between the magnetic moments of the Fe-and Tm-sublattices.展开更多
The site occupancies in permanent magnetic alloy Y_2(Fe_(0.95)Al_(0.05))_(14)B has been studied by means of neutron diffraction.The results from profile refinement show that Al enters the tetragonal structure of Nd_2F...The site occupancies in permanent magnetic alloy Y_2(Fe_(0.95)Al_(0.05))_(14)B has been studied by means of neutron diffraction.The results from profile refinement show that Al enters the tetragonal structure of Nd_2Fe_(14)B and occupies the 4c and 8j_2 sites of the space group P4_2/mnm preferably.The relation between the site occupancies and the magnetic proper- ties is discussed preliminarily.展开更多
To analyze the magnetic properties of Nd_(2)Fe_(14)B compound under high pressure,an improved two-sublattice molecular field model coupled with equivalent stress field was applied to study the effect of pressure on ma...To analyze the magnetic properties of Nd_(2)Fe_(14)B compound under high pressure,an improved two-sublattice molecular field model coupled with equivalent stress field was applied to study the effect of pressure on magnetization,magnetostriction coefficient,susceptibility and Curie temperature.The calculation results show that the pressure has a stronger effect on the magnetization of Fe sublattice compared to that of Nd sublattice at varied temperatures when the external magnetic field is parallel to the alignment direction.Saturated magnetization,initial susceptibility and magnetic moment of Nd_(2)Fe_(14)B compound are found to decrease gradually with pressure increasing,and the Curie temperature of Nd_(2)Fe_(14)B decreases to about 298 K under an applied pressure of 1.15 GPa.The results suggest that the pressure-induced magnetic phase transition of Nd2Fe14B occurs under 1.15 GPa at room temperature.展开更多
In order to obtain ultrafine Nd-Fe-B powder, a spray-dried precursor was treated by reduction-diffusion (R/D) process. And, unlike the conventional R/D process, calcium reduction that is a crucial step for the formati...In order to obtain ultrafine Nd-Fe-B powder, a spray-dried precursor was treated by reduction-diffusion (R/D) process. And, unlike the conventional R/D process, calcium reduction that is a crucial step for the formation of Nd2Fe14B was performed without conglomerating the precursor with Ca powder. By adopting this modified process, it is possible to synthesize the hard magnetic Nd2Fe14B at the reaction temperature as low as 850 ℃. The average size of Nd2Fe14B particles that are uniformly distributed in the optimally treated powder was <<1 μm. Most Nd2Fe14B particles were enclosed with thin layers of Nd-rich phase. Typical magnetic properties of such powder without eliminating impurity CaO were iHc=～5.9 kOe, Br=～5.5 kG, and (BH)max=～6 MGOe.展开更多
This review summarizes the recent advances on the application of ^(57)Fe Mössbauer spectrometry to study the magnetic and phase characteristics of Nd–Fe–B-based permanent magnets. First of all, the hyperfine st...This review summarizes the recent advances on the application of ^(57)Fe Mössbauer spectrometry to study the magnetic and phase characteristics of Nd–Fe–B-based permanent magnets. First of all, the hyperfine structures of the Ce_(2)Fe_(14)B,(Ce,Nd)_(2)Fe_(14)B and MM_(2)Fe_(14)B phases are well-defined by using the model based on the Wigner-Seitz analysis of the crystal structure. The results show that the isomer shift δ and the quadrupole splitting öEQ of those 2:14:1 phases show minor changes with the Nd content, while the hyperfine field Bhfincreases monotonically with increasing Nd content and its value is influenced by the element segregation and phase separation in the 2:14:1 phase. Then, the hyperfine structures of the low fraction secondary phases are determined by the ^(57)Fe Mössbauer spectrometry due to its high sensitivity. On this basis,the content, magnetic behavior, and magnetization of the REFe_(2) phase, the amorphous grain boundary(GB) phase, and the amorphous worm-like phase, as well as their effects on the magnetic properties, are systematically studied.展开更多
To search for proper alternatives to improve the magnetic properties of Nd_(2)Fe_(14)B,using first-principles density functional theory calculations we have systematically studied the R_(2)M_(14)B(R=lanthanides from L...To search for proper alternatives to improve the magnetic properties of Nd_(2)Fe_(14)B,using first-principles density functional theory calculations we have systematically studied the R_(2)M_(14)B(R=lanthanides from La to Lu;M=Mn,Fe,Co,and Ni)compounds with the isomorphic structure of Nd_(2)Fe_(14)B.The results show that for rare-earth elements,Pr is the most suitable choice for considering as an alternative of Nd.As for the substitution of Fe in Nd_(2)Fe_(14) B by other transition-metal elements,Co is much more suitable than Mn and Ni because the latter two result in too significant reduction of the magnetic moment.展开更多
To search for an alternative for Nd_(2)Fe_(14)B,we have studied the electronic structures of R_(2)M_(14)B compounds,where R stands for rare-earth element and M for Mn,Fe,Co and Ni.By density functional theory(DFT),we ...To search for an alternative for Nd_(2)Fe_(14)B,we have studied the electronic structures of R_(2)M_(14)B compounds,where R stands for rare-earth element and M for Mn,Fe,Co and Ni.By density functional theory(DFT),we discuss the atomic coordination environment and partial density of states(PDOS)in detail,with the emphasis on the interaction between the six kinds of M sites and the R atoms.We systemically calculated the electronic structures of sixty R_(2)M_(14)B compounds to provide systematic and reliable results for explaining the origination of magnetism,which is important for further development of Nd_(2)Fe_(14)B based magnet materials.展开更多
基金This work was financially supported by the Zhejiang Provincial Natural Science Fund of China(No.M503096)by Ministry of Science and Technology(No.2004CCA04000).
文摘The arrangements of the easy magnetization axis[001]of columnar Nd_(2)Fe_(14)B crystals in the laser scanned layer on anisotropic sintered Nd_(15)Fe_(77)B_(8)magnets were investigated by XRD and the Bitter method.The results show that the common effects of both the heat flux and the substrate magnetization orientation constrain the columnar Nd_(2)Fe_(14)B solidified from the laser melting pool to form the c-axis texture orientated with the same direction as that of the substrate,when the geometric relationship between the heat flux in the laser scanning layer and c-axis texture orientation of the substrate is perpendicular to each other,and if the laser scanning velocity is no less than 25 mm·min^(-1).The c-axes of columnar Nd_(2)Fe_(14)B crystals are no longer randomly distributed in the plane normal to their preferential growing direction as they are randomly done in both ingots cooled by water-cooling copper mould and directionally solidified Nd-Fe-B rods.
文摘Texture evolution in nanocomposite Nd_2Fe_ 14B/α-Fe magnets prepared by direct melt spinning was investigated. The free surface and wheel-contacted surface exhibit different texture direction. Modification of composition not only enhances magnetic properties, but also changes texture direction of the ribbon. Low temperature heat treatment can increase the magnetic properties to some extent, and high temperature annealing decreases the magnetic properties. Both low and high temperature heat treatment have effects on grain orientation, but the difference still exists between the two surfaces of the ribbon. So it is infeasibility to prepare anisotropic Nd_2Fe_ 14B/α-Fe nanocomposite magnets by direct melt spinning.
文摘Based on the observation of temperature variation of both domain structure and magnetic con- trast.the thermal demagnetization and randomness of domain nucleation was discussed.
基金the National Advanced Technology Research and Development Committee of China (2002AA302602-2) Shanghai Municipal Development Foundation of Science and Technology (0552nm049)+1 种基金Shanghai institute of Technolo-gy (YJ-2006-16)Project (P1502) Supported by Shanghai Leading Academic Discipline
文摘Microstructure and magnetic properties of Nd8.5Fe77.1B6.4Co4Zr3Nb0.5V0.5 nanocomposite ribbons were investigated. A fine and uniform grain with 30 nm in average size was achieved for the ribbons annealed at 710 ℃ for 4 min, which enhanced the interaction coupling between grains and improved the magnetic properties. The results of three-dimensional atom probe (3DAP) revealed that V-enriched intergranular phase existed at the grain boundaries, suppressing the grain growth during crystallization process. The remanence and coercivity for annealed ribbons reached to 80 emu·g-1 and 567 kA·m-1, respectively.
基金This work has been supported by the National Natural Science Foundation of P.R.China(5870025)Magnetism Laboratory of Institute of Physics,Beijing,P.R.China.
文摘Easy and hard magnetization curves of Nd_2Co_(14)B compound have been measured with extracting-sample-magnetometer(μ_0H_(max)=6T)at 10～300 K.Magnetic anisotropy constants K_1 and K_2 have been determined by fitting the hard magnetization curves,in which only K_1 ,K_2 and misalignment angle have been taken as fitting parameters.The values of K_1 and K_2 at 4.2 K were derived by extrapolation. Anisotropy coefficients,x_2~° and x_4~°were derived from the anisotropy constants.The anisotropy constant K_2 increases rapidly with increasing temperature when T<T_(sr)and slowly when T>T_(sr).The temperature depen- dence of the magnetic anisotropy coefficient x_2~° was fitted with the formula.The anisotropy coefficients x_2~° can be well described by the tenth-power law from 4.2 K to T_(sr)and by the sixth-power law from T_(sr_ to 300 K.
文摘A series of magnetic properties of Tm_2Fe_(14)B are explained quantitatively by the calculations based on the single ion model. The magnetic properties include the temperature dependence of the spontaneous magnetization, the spin reorientation temperature and the magnetization curves along the principal crystal axes at 4.2, 100, 150 and 200 K. The values of the exchange field and the crystalline electric field parameters used in the calculations are μ_BH_(ex)(T=0 K)=135, B_2~0=1.77, B_2~2=±2.97, B_4~0=-3.06×10^(-3), B_4^(-2)=0, B_4~4=-6.82×10^(-3), B_6~0=1.05× 10^(-5), B_6^(-2)=±7.40×10^(-5), B_6~4=1.96×10^(-4), and B_6^(-6)=0 all in K unit. The magnetization processes of the Fe-and Tm-sublattices at different temperatures are analysed. The processes are characterized by the non-collinearity between the magnetic moments of the Fe-and Tm-sublattices.
文摘The site occupancies in permanent magnetic alloy Y_2(Fe_(0.95)Al_(0.05))_(14)B has been studied by means of neutron diffraction.The results from profile refinement show that Al enters the tetragonal structure of Nd_2Fe_(14)B and occupies the 4c and 8j_2 sites of the space group P4_2/mnm preferably.The relation between the site occupancies and the magnetic proper- ties is discussed preliminarily.
基金This study was financially supported by the National Natural Science Foundation of China(No.11072036).
文摘To analyze the magnetic properties of Nd_(2)Fe_(14)B compound under high pressure,an improved two-sublattice molecular field model coupled with equivalent stress field was applied to study the effect of pressure on magnetization,magnetostriction coefficient,susceptibility and Curie temperature.The calculation results show that the pressure has a stronger effect on the magnetization of Fe sublattice compared to that of Nd sublattice at varied temperatures when the external magnetic field is parallel to the alignment direction.Saturated magnetization,initial susceptibility and magnetic moment of Nd_(2)Fe_(14)B compound are found to decrease gradually with pressure increasing,and the Curie temperature of Nd_(2)Fe_(14)B decreases to about 298 K under an applied pressure of 1.15 GPa.The results suggest that the pressure-induced magnetic phase transition of Nd2Fe14B occurs under 1.15 GPa at room temperature.
文摘In order to obtain ultrafine Nd-Fe-B powder, a spray-dried precursor was treated by reduction-diffusion (R/D) process. And, unlike the conventional R/D process, calcium reduction that is a crucial step for the formation of Nd2Fe14B was performed without conglomerating the precursor with Ca powder. By adopting this modified process, it is possible to synthesize the hard magnetic Nd2Fe14B at the reaction temperature as low as 850 ℃. The average size of Nd2Fe14B particles that are uniformly distributed in the optimally treated powder was <<1 μm. Most Nd2Fe14B particles were enclosed with thin layers of Nd-rich phase. Typical magnetic properties of such powder without eliminating impurity CaO were iHc=～5.9 kOe, Br=～5.5 kG, and (BH)max=～6 MGOe.
基金Project supported by the Zhejiang Provincial Natural Science Foundation of China(Grant Nos.LY20E010002,LR18E010001,and LD19E010001)the National Natural Science Foundation of China(Grant Nos.U1704253 and 51801047)+2 种基金Liaoning Revitalization Talents Program(Grant No.XLYC1807177)the Key Research and Development plan of Zhejiang Province,China(Grant No.2020C05014)Ten Thousand Talents Plan of Zhejiang Province,China(Grant No.2018R52003)。
文摘This review summarizes the recent advances on the application of ^(57)Fe Mössbauer spectrometry to study the magnetic and phase characteristics of Nd–Fe–B-based permanent magnets. First of all, the hyperfine structures of the Ce_(2)Fe_(14)B,(Ce,Nd)_(2)Fe_(14)B and MM_(2)Fe_(14)B phases are well-defined by using the model based on the Wigner-Seitz analysis of the crystal structure. The results show that the isomer shift δ and the quadrupole splitting öEQ of those 2:14:1 phases show minor changes with the Nd content, while the hyperfine field Bhfincreases monotonically with increasing Nd content and its value is influenced by the element segregation and phase separation in the 2:14:1 phase. Then, the hyperfine structures of the low fraction secondary phases are determined by the ^(57)Fe Mössbauer spectrometry due to its high sensitivity. On this basis,the content, magnetic behavior, and magnetization of the REFe_(2) phase, the amorphous grain boundary(GB) phase, and the amorphous worm-like phase, as well as their effects on the magnetic properties, are systematically studied.
基金supported by the National Natural Science Foundation of China(No.21703248)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB20000000)the STS program under cooperative agreement between Fujian Province and Chinese Academy of Sciences(No 2017T3004)。
文摘To search for proper alternatives to improve the magnetic properties of Nd_(2)Fe_(14)B,using first-principles density functional theory calculations we have systematically studied the R_(2)M_(14)B(R=lanthanides from La to Lu;M=Mn,Fe,Co,and Ni)compounds with the isomorphic structure of Nd_(2)Fe_(14)B.The results show that for rare-earth elements,Pr is the most suitable choice for considering as an alternative of Nd.As for the substitution of Fe in Nd_(2)Fe_(14) B by other transition-metal elements,Co is much more suitable than Mn and Ni because the latter two result in too significant reduction of the magnetic moment.
基金supported by the National Natural Science Foundation of China(No.21703248)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB20000000)the STS program under cooperative agreement between Fujian Province and Chinese Academy of Sciences(No.2017T3004)。
文摘To search for an alternative for Nd_(2)Fe_(14)B,we have studied the electronic structures of R_(2)M_(14)B compounds,where R stands for rare-earth element and M for Mn,Fe,Co and Ni.By density functional theory(DFT),we discuss the atomic coordination environment and partial density of states(PDOS)in detail,with the emphasis on the interaction between the six kinds of M sites and the R atoms.We systemically calculated the electronic structures of sixty R_(2)M_(14)B compounds to provide systematic and reliable results for explaining the origination of magnetism,which is important for further development of Nd_(2)Fe_(14)B based magnet materials.
