The coercivity mechanism of Nd-Fe-B based magnets prepared by a new techniqueof strip casting was investigated. Different from the traditional magnets, α-Fe phases aredifficult to be found in Nd-Fe-B magnets prepared...The coercivity mechanism of Nd-Fe-B based magnets prepared by a new techniqueof strip casting was investigated. Different from the traditional magnets, α-Fe phases aredifficult to be found in Nd-Fe-B magnets prepared by strip casting. Meanwhile, the rich-Nd phasesoccur not only near the grain boundaries of main phases, but also within the main-phase grains.Investigation on the magnetizing field dependence of the coercivity for the(Nd_(0.935)Dy_(0.065))_(14.5)Fe_(79.4)B_(6.1) magnet and the temperature dependence of thecoercivity for the Nd_(14.5)Fe_(79.4)B_(6.1) magnet hav been done. Results show that coercivitiesfor strip casting magnets are controlled by the nucleation mechanism.展开更多
In this paper,we systematically investigated the microstructure evolution and coercivity mechanism of hydrogenation-disproportionation-desorption-recombination(HDDR)treated Nd-Fe-B strip cast alloys by transmission el...In this paper,we systematically investigated the microstructure evolution and coercivity mechanism of hydrogenation-disproportionation-desorption-recombination(HDDR)treated Nd-Fe-B strip cast alloys by transmission electron microscopy(TEM)and three-dimensional atom probe(3 DAP)analyses.The rodlike NdH_(2+x) phases with diameters of 10-20 nm are embedded intoα-Fe matrix,which hereditarily leads to textured grains in HDDR alloy.The migration of NdH_(2+x) from Nd-rich region toα-Fe matrix during hydrogen absorption process contributes to the uniform redistribution of Nd-rich phases after HDDR treatment The HDDR alloy with single domain grain sizes of 200-300 nm exhibits relatively low coercivity of 1.01 T that arises from pinning magnetic domain motion.The weak c-axis orientation of HDDR alloy results in a lower reverse magnetic field(coercivity)to reduce remanence to 0.Moreover,the direct contact of Nd_(2)Fe_(14)B grains and the high concentration of ferromagnetic elements(Fe content≈66.06 at%,Co content≈0.91 at%)in Nd-rich grain boundary layer lead to strong magnetostatic coupling effect among Nd_(2) Fe_(14)B grains.The nano-sized a-Fe inside Nd_(2) Fe_(14)B matrix makes the magnetization reversal easily and decreases the coercivity of HDDR alloy.展开更多
The purpose of this paper is to study the influence of Mo addition on the phase morphologies,microstructures and magnetic properties of the designated alloys.It is found out that the coercivity H_(cj) increases uneven...The purpose of this paper is to study the influence of Mo addition on the phase morphologies,microstructures and magnetic properties of the designated alloys.It is found out that the coercivity H_(cj) increases unevenly from 12.2 kOe for(Nd_(0.8)Ce_(0.2))_(13)Fe_(82)B_(5) to the maximum value of 13.3 kOe for(Nd_(0.8)Ce_(0.2))_(13)Fe_(80)B_(5)Mo_(2).The transmission electron microscopy images demonstrate that the grain size decreases with the addition of Mo,which indicates that Mo has grain refinement effect.The correlative analysis gives rise to the conclusion that the coercivity mechanism of the investigated alloys is dominated by pinning type.All in all,the enhancement of the magnetic properties is mainly attributed to the synergistic impact of grain refinement,pinning effects and the micro structural homogenization.The research may shed light on the potential development and application of rare earth-based counterpart magnets.展开更多
Sm(Co_(bal)Fe_(0.245)Cu_(0.07)Zr_(0.02))7.8(at%)sintered magnets with high remanence(B_(r)~1.15 T)were prepared using a traditional powder metallurgy method.Tunable magnetic properties,especially intrinsic coercivity(...Sm(Co_(bal)Fe_(0.245)Cu_(0.07)Zr_(0.02))7.8(at%)sintered magnets with high remanence(B_(r)~1.15 T)were prepared using a traditional powder metallurgy method.Tunable magnetic properties,especially intrinsic coercivity(H_(cj)),were obtained through adjusting isothermal procedure parameters.H_(cj)of the magnets increases from 305 to 752 kA·m^(-1)with isothermal annealing time increasing from 3 to 20 h,while B_(r) of the magnets almost keeps constant.From the bright field transmission electron microscopy(TEM)images,it is found that:(1)there is dispersed precipitated phase with very small size in the magnet annealed for 3 h,while the magnets annealed for 20 h have distinct and intact cellular structure;(2)the number density of Z-phase in magnet annealed for 20 h is bigger than that for 3 h.Besides,the finer microstructures were studied with high-resolution transmission electron microscopy(HRTEM).展开更多
PrCo5 nanoflakes with strong texture and high coercivity of 8.15 kOe were prepared by surfactant-assisted ball milling with heat-treated starting powder. The thickness and length of the as-milled nanoflakes are mainly...PrCo5 nanoflakes with strong texture and high coercivity of 8.15 kOe were prepared by surfactant-assisted ball milling with heat-treated starting powder. The thickness and length of the as-milled nanoflakes are mainly in the ranges of 50–100 nm and 0.5–3 μm, respectively. The x-ray diffraction patterns demonstrate that the heat treatment can increase the single phase and crystallinity of the PrCo5 compound, and combined with the demagnetization curves, indicate that the single phase and crystallinity are important for preparing high-coercivity and strong-textured rare earth permanent magnetic nanoflakes. In addition, the coercivity mechanism of the as-milled PrCo5 nanoflakes is studied by the angle dependence of coercivity for an aligned sample and the field dependence of coercivity, isothermal(IRM) and dc demagnetizing(DCD)remanence curves for an unaligned sample. The results indicate that the coercivity is dominated by co-existing mechanisms of pinning and nucleation. Furthermore, exchange coupling and dipolar coupling also co-exist in the sample.展开更多
Experimental and theoretical researches on nanostructured exchange coupled magnets have been carried out since about 1988. Here, we review the structure and magnetic properties of the anisotropic nanocomposite soft/ha...Experimental and theoretical researches on nanostructured exchange coupled magnets have been carried out since about 1988. Here, we review the structure and magnetic properties of the anisotropic nanocomposite soft/hard multilayer magnets including some new results and phenomena from an experimental point of view. According to the different component of the oriented hard phase in the nanocomposite soft/hard multilayer magnets, three types of magnets will be discussed:1) anisotropic Nd2Fe(14)B based nanocomposite multilayer magnets, 2) anisotropic SmCo5 based nanocomposite multilayer magnets, and 3) anisotropic rare-earth free based nanocomposite multilayer magnets. For each of them, the formation of the oriented hard phase, exchange coupling, coercivity mechanism, and magnetic properties of the corresponding anisotropic nanocomposite multilayer magnets are briefly reviewed, and then the prospect of realization of bulk magnets on new results of anisotropic nanocomposite multilayer magnets will be carried out.展开更多
This paper reports that the SmCo6.8Zr0.2 nanocrystalline permanent magnets and SmCo6.8Zr0.2/a-(Fe,Co) nanocomposite permanent magnets are successfully produced by mechanical alloying and subsequently annealing at 70...This paper reports that the SmCo6.8Zr0.2 nanocrystalline permanent magnets and SmCo6.8Zr0.2/a-(Fe,Co) nanocomposite permanent magnets are successfully produced by mechanical alloying and subsequently annealing at 700℃ for 10 minutes. The x-ray diffraction results show that the phase structure of SmCo6.8Zr0.2 nanocrystalline permanent magnets is composed of SmCo7 phase and SmCo6.8Zr0.2/a-(Fe,Co) nanocomposite permanent magnets is composed of SmCo7 and a-(Fe,Co) phases. The mechanism of magnetization reversal is mainly controlled by inhomogeneous domain wall pinning in SmCo6.8Zr0.2 and SmCo6.8Zr0.2/a-(Fe,Co) magnets. The inter-grain exchange interaction at low temperature is investigated, which shows that the inter-grain exchange interaction of SmCo6.8Zr0.2/a-(Fe,Co) magnets increases greatly by the decrease of the measured temperature. According to Amirr-H/Hcj, Amrev-H/Hcj and Xirr-H/Hcj curves at room temperature and 100 K, the changes of irreversible and reversible magnetization behaviours of SmCo6.8Zr0.2 and SmCo6.8Zr0.2/a-(Fe,Co) magnets with the decreasing temperature are analysed in detail. The magnetic viscosity and the activation volume of SmCo6.8Zr0.2 and SmCo6.8Zr0.2/a-(Fe,Co) magnets at different temperatures are also studied.展开更多
Effects of low-melting Pr-Cu alloy addition on the microstructure and magnetic properties of the hot-deformation Nd-Fe-B magnets were investigated.A small amount of Pr-Cu addition enhances the coercivity of the hot-de...Effects of low-melting Pr-Cu alloy addition on the microstructure and magnetic properties of the hot-deformation Nd-Fe-B magnets were investigated.A small amount of Pr-Cu addition enhances the coercivity of the hot-deformation Nd-Fe-B magnets obviously.The coercivity of the hotdeformation Nd-Fe-B magnets with 4.0 wt%Pr_(85)Cu_(15)addition increases to 1271 kA·m^(-1),75.69%higher than that of Pr-Cu-free magnet(723 kA·m^(-1)),and then decreases with5 wt%Pr_(85)Cu_(15)addition.It is observed that there a uniform RE-rich phase is formed wrapping the Nd2Fe14B main phase in the sample with 4.0%Pr_(85)Cu_(15)addition by scanning electron microscopy(SEM),which promotes the coercivity.The angular dependence of coercivity for the hot-deformation Nd-Fe-B magnets indicates that the coercivity mechanism is nucleation combined with domain wall pinning.The domain wall pinning is weakened,while the nucleation is enhanced after Pr-Cu addition.Theremanence,intrinsic coercivity,and maximum magnetic energy product of the original Nd-Fe-B magnet are 1.45 T,723 kA·m^(-1),and 419.8 kJ·m^(-3),respectively,and those of the sample with 4.0%Pr_(85)Cu_(15)alloy addition are 1.30 T,1271 kA·m^(-1),and 330.0 kJ·m^(-3),respectively.展开更多
The coercivity,microstructure,and magnetic domain structure of Nd-Fe-B sintered magnets by grain boundary diffusion process(GBDP) with TbH3 nanoparticles were systematically investigated.Compared to the original magne...The coercivity,microstructure,and magnetic domain structure of Nd-Fe-B sintered magnets by grain boundary diffusion process(GBDP) with TbH3 nanoparticles were systematically investigated.Compared to the original magnet,the coercivity(Hci) of the GBDP magnets improved from 1702 to 2374 kA·m^(-1) with few remanence reduced from 1.338 to 1.281 T.Electron probe microanalysis(EPMA) analysis showed that Tb diffused along grain boundary,mainly concentrated in the boundary layer of the main phase,and formed a core-shell structure.Magneto-optical Kerr optical microscope(MOKE) analysis showed that there were two types of magnetic domain reversal in one grain:gradual reversal(GR) and abrupt reversal(AR).When the applied field decreased from saturated magnetic field,the reversal magnetic domain nucleated and then spread over the whole grain gradually,which was called GR.However,some grains kept the single domain state until Hh which was a value of reverse direction applied field in second quadrant in hysteresis loops.When the applied field increased above Hh,reversed magnetic domain would suddenly appear and occupy most of the area of the grain,which was called AR.That is because AR grains have higher reversed magnetic domain nucleation field(HRN2) than GR grains(HRN1).After GBDP,the area of AR region increased obviously and GR region decreased accordingly,indicating that the core-shell structure could change GR grain into AR grain.The coreshell structure could suppress flipping of the magnetization of the grains due to the large magnetic anisotropy of Tbrich shell.Therefore,large AR area led to high coercivity.展开更多
In the present work,the magnetization reversal behavior for the melt spinning(Nd_(0.8)Ce_(0.2))_(2)Fe_(12)Co_(2-x)Zr_(x)B(x=0,0.5)permanent alloys with high coercivity was investigated by analyzing the hysteresis curv...In the present work,the magnetization reversal behavior for the melt spinning(Nd_(0.8)Ce_(0.2))_(2)Fe_(12)Co_(2-x)Zr_(x)B(x=0,0.5)permanent alloys with high coercivity was investigated by analyzing the hysteresis curves and the recoil loops.Compared to the Zr-free alloy,the Zr-doped sample obtains higher magnetic properties:coercivity of H_(cj)=650.5 kA·m^(-1),squareness of H_(k)/H_(cj)=0.76 and maximum energy product of(BH)_(max)=131.0 kJ·m^(-3).The first-order reversal curves(FORCs)analysis was taken to identify optimal conditions of exchange coupling for the Zr-free and Zr-doped alloys.The coercivity mechanism of theα-Fe/Nd_(2)Fe_(14)B nanocomposite alloys was analyzed by the angular dependence of the coercive field as measured for the Zr-doped sample.The results show that the magnetic reverse process of the Zr-doped sample can be explained by the pinning model.展开更多
Sm-Co permanent magnets are widely used in aerospace equipments,tubes,sensors and hybrid electric vehicles due to their excellent magnetic properties at both room and high temperatures.Compared to that of Nd-Fe-B magn...Sm-Co permanent magnets are widely used in aerospace equipments,tubes,sensors and hybrid electric vehicles due to their excellent magnetic properties at both room and high temperatures.Compared to that of Nd-Fe-B magnets,the capability of reliably operating at temperatures up to 500℃ is the biggest preponderance of Sm-Co permanent magnets.However,the reliable high-temperature magnetic properties are susceptible to composition and technique processes.So,appropriate composition and matched technique processes are prerequisites for good high-temperature magnetic properties.This review mainly emphasizes the influences of Sm,Fe,Cu and Zr contents and technique processes on development of high-temperature performance and discusses the controversial hightemperature coercivity mechanism of 2:17-type high-temperature Sm-Co magnets.展开更多
Highly ordered Tb_(x)Fe_(7)Co_(3)(x=0,0.6,0.8)nanowires were synthesized in alumina templates by electrochemical deposition method.Here,the effects of Tb content and annealing treatment on the phase composition,morpho...Highly ordered Tb_(x)Fe_(7)Co_(3)(x=0,0.6,0.8)nanowires were synthesized in alumina templates by electrochemical deposition method.Here,the effects of Tb content and annealing treatment on the phase composition,morphology,crystalline structure and magnetic properties were investigated.The asdeposited Tb_0 Fe_(7)Co_(3)nanowires comprise Fe_(7)Co_(3)phase.While after adding Tb,the diffraction peaks slightly shift left,indicating the infiltration of Tb atoms into Fe_(7)Co_(3)phase.After annealing,Tb_0 Fe_(7)Co_(3)nanowires still consist of Fe_(7)Co_(3)phase with a slight enhancement on coercivity.While the annealed nanowires with Tb doped present a complex phase composition containing Fe3 Tb,Fe_(2)Tb,Co_(3)Tb,Co_(17)Tb_(2),TbFeO_(3)and Fe_(2)O_(3)phases distribute in the central portion,and Co_(0.72)Fe_(0.28)at the nanowire outer walls.The annealed Tb_(x)Fe_(7)Co_(3)(x=0.6,0.8)nanowires show higher magnetic performance owing to the formation of hard magnetic phases,the interfacial elastic coupling between hard and soft phases and the coherent Fe3 Tb/Co_(3)Tb interface which restrain the domain wall motion.To be specific,the coercivity and remanence ratio of TbxFe_(7)Co_(3)(x=0.6,0.8)nanowires significantly enhance with increasing Tb content.展开更多
基金This work is supported by the National Natural Science Foundation of China (No. 50271036).
文摘The coercivity mechanism of Nd-Fe-B based magnets prepared by a new techniqueof strip casting was investigated. Different from the traditional magnets, α-Fe phases aredifficult to be found in Nd-Fe-B magnets prepared by strip casting. Meanwhile, the rich-Nd phasesoccur not only near the grain boundaries of main phases, but also within the main-phase grains.Investigation on the magnetizing field dependence of the coercivity for the(Nd_(0.935)Dy_(0.065))_(14.5)Fe_(79.4)B_(6.1) magnet and the temperature dependence of thecoercivity for the Nd_(14.5)Fe_(79.4)B_(6.1) magnet hav been done. Results show that coercivitiesfor strip casting magnets are controlled by the nucleation mechanism.
基金Project supported by the State Key Laboratory for Advanced Metals and Materials(2019Z-14)。
文摘In this paper,we systematically investigated the microstructure evolution and coercivity mechanism of hydrogenation-disproportionation-desorption-recombination(HDDR)treated Nd-Fe-B strip cast alloys by transmission electron microscopy(TEM)and three-dimensional atom probe(3 DAP)analyses.The rodlike NdH_(2+x) phases with diameters of 10-20 nm are embedded intoα-Fe matrix,which hereditarily leads to textured grains in HDDR alloy.The migration of NdH_(2+x) from Nd-rich region toα-Fe matrix during hydrogen absorption process contributes to the uniform redistribution of Nd-rich phases after HDDR treatment The HDDR alloy with single domain grain sizes of 200-300 nm exhibits relatively low coercivity of 1.01 T that arises from pinning magnetic domain motion.The weak c-axis orientation of HDDR alloy results in a lower reverse magnetic field(coercivity)to reduce remanence to 0.Moreover,the direct contact of Nd_(2)Fe_(14)B grains and the high concentration of ferromagnetic elements(Fe content≈66.06 at%,Co content≈0.91 at%)in Nd-rich grain boundary layer lead to strong magnetostatic coupling effect among Nd_(2) Fe_(14)B grains.The nano-sized a-Fe inside Nd_(2) Fe_(14)B matrix makes the magnetization reversal easily and decreases the coercivity of HDDR alloy.
基金financially supported by the Jiangxi University of Science and Technology under excellent doctoral thesis cultivation project(No.3105500035)the Science and Technology Program of Fujian Province(No.2017T3001)the National Natural Science Foundation of China(No.51564037)。
文摘The purpose of this paper is to study the influence of Mo addition on the phase morphologies,microstructures and magnetic properties of the designated alloys.It is found out that the coercivity H_(cj) increases unevenly from 12.2 kOe for(Nd_(0.8)Ce_(0.2))_(13)Fe_(82)B_(5) to the maximum value of 13.3 kOe for(Nd_(0.8)Ce_(0.2))_(13)Fe_(80)B_(5)Mo_(2).The transmission electron microscopy images demonstrate that the grain size decreases with the addition of Mo,which indicates that Mo has grain refinement effect.The correlative analysis gives rise to the conclusion that the coercivity mechanism of the investigated alloys is dominated by pinning type.All in all,the enhancement of the magnetic properties is mainly attributed to the synergistic impact of grain refinement,pinning effects and the micro structural homogenization.The research may shed light on the potential development and application of rare earth-based counterpart magnets.
基金the National Basic Research Program of China(No.2014CB643701)the National Natural Science Foundation of China(No.51171048)。
文摘Sm(Co_(bal)Fe_(0.245)Cu_(0.07)Zr_(0.02))7.8(at%)sintered magnets with high remanence(B_(r)~1.15 T)were prepared using a traditional powder metallurgy method.Tunable magnetic properties,especially intrinsic coercivity(H_(cj)),were obtained through adjusting isothermal procedure parameters.H_(cj)of the magnets increases from 305 to 752 kA·m^(-1)with isothermal annealing time increasing from 3 to 20 h,while B_(r) of the magnets almost keeps constant.From the bright field transmission electron microscopy(TEM)images,it is found that:(1)there is dispersed precipitated phase with very small size in the magnet annealed for 3 h,while the magnets annealed for 20 h have distinct and intact cellular structure;(2)the number density of Z-phase in magnet annealed for 20 h is bigger than that for 3 h.Besides,the finer microstructures were studied with high-resolution transmission electron microscopy(HRTEM).
基金Project supported by the National Basic Research Program of China(Grant No.2014CB643702)the National Natural Science Foundation of China(Grant No.51401235)Beijing Natural Science Foundation,China(Grant No.2152034)
文摘PrCo5 nanoflakes with strong texture and high coercivity of 8.15 kOe were prepared by surfactant-assisted ball milling with heat-treated starting powder. The thickness and length of the as-milled nanoflakes are mainly in the ranges of 50–100 nm and 0.5–3 μm, respectively. The x-ray diffraction patterns demonstrate that the heat treatment can increase the single phase and crystallinity of the PrCo5 compound, and combined with the demagnetization curves, indicate that the single phase and crystallinity are important for preparing high-coercivity and strong-textured rare earth permanent magnetic nanoflakes. In addition, the coercivity mechanism of the as-milled PrCo5 nanoflakes is studied by the angle dependence of coercivity for an aligned sample and the field dependence of coercivity, isothermal(IRM) and dc demagnetizing(DCD)remanence curves for an unaligned sample. The results indicate that the coercivity is dominated by co-existing mechanisms of pinning and nucleation. Furthermore, exchange coupling and dipolar coupling also co-exist in the sample.
基金Project supported by the State Key Project of Research and Development of China(Grant No.2017YFA0206302)the National Nature Science Foundation of China(Grant Nos.51590883,51331006,and 51471167)the Chinese Academy of Sciences(Grant No.KJZD-EW-M05-3)
文摘Experimental and theoretical researches on nanostructured exchange coupled magnets have been carried out since about 1988. Here, we review the structure and magnetic properties of the anisotropic nanocomposite soft/hard multilayer magnets including some new results and phenomena from an experimental point of view. According to the different component of the oriented hard phase in the nanocomposite soft/hard multilayer magnets, three types of magnets will be discussed:1) anisotropic Nd2Fe(14)B based nanocomposite multilayer magnets, 2) anisotropic SmCo5 based nanocomposite multilayer magnets, and 3) anisotropic rare-earth free based nanocomposite multilayer magnets. For each of them, the formation of the oriented hard phase, exchange coupling, coercivity mechanism, and magnetic properties of the corresponding anisotropic nanocomposite multilayer magnets are briefly reviewed, and then the prospect of realization of bulk magnets on new results of anisotropic nanocomposite multilayer magnets will be carried out.
基金Project supported by the Natural Science Foundation of Zhejiang Province of China (Grant No.Y407174)Major Scientific and Technological Special Fund of Zhejiang Province of China (Grant No.2007C11046)the National Basic Research Program of China (Grant No.2010CB934601)
文摘This paper reports that the SmCo6.8Zr0.2 nanocrystalline permanent magnets and SmCo6.8Zr0.2/a-(Fe,Co) nanocomposite permanent magnets are successfully produced by mechanical alloying and subsequently annealing at 700℃ for 10 minutes. The x-ray diffraction results show that the phase structure of SmCo6.8Zr0.2 nanocrystalline permanent magnets is composed of SmCo7 phase and SmCo6.8Zr0.2/a-(Fe,Co) nanocomposite permanent magnets is composed of SmCo7 and a-(Fe,Co) phases. The mechanism of magnetization reversal is mainly controlled by inhomogeneous domain wall pinning in SmCo6.8Zr0.2 and SmCo6.8Zr0.2/a-(Fe,Co) magnets. The inter-grain exchange interaction at low temperature is investigated, which shows that the inter-grain exchange interaction of SmCo6.8Zr0.2/a-(Fe,Co) magnets increases greatly by the decrease of the measured temperature. According to Amirr-H/Hcj, Amrev-H/Hcj and Xirr-H/Hcj curves at room temperature and 100 K, the changes of irreversible and reversible magnetization behaviours of SmCo6.8Zr0.2 and SmCo6.8Zr0.2/a-(Fe,Co) magnets with the decreasing temperature are analysed in detail. The magnetic viscosity and the activation volume of SmCo6.8Zr0.2 and SmCo6.8Zr0.2/a-(Fe,Co) magnets at different temperatures are also studied.
基金financially supported by the National Natural Science Foundation of China(No.51331003)the Major State Basis Research Development Program of China(No.2014CB643701)。
文摘Effects of low-melting Pr-Cu alloy addition on the microstructure and magnetic properties of the hot-deformation Nd-Fe-B magnets were investigated.A small amount of Pr-Cu addition enhances the coercivity of the hot-deformation Nd-Fe-B magnets obviously.The coercivity of the hotdeformation Nd-Fe-B magnets with 4.0 wt%Pr_(85)Cu_(15)addition increases to 1271 kA·m^(-1),75.69%higher than that of Pr-Cu-free magnet(723 kA·m^(-1)),and then decreases with5 wt%Pr_(85)Cu_(15)addition.It is observed that there a uniform RE-rich phase is formed wrapping the Nd2Fe14B main phase in the sample with 4.0%Pr_(85)Cu_(15)addition by scanning electron microscopy(SEM),which promotes the coercivity.The angular dependence of coercivity for the hot-deformation Nd-Fe-B magnets indicates that the coercivity mechanism is nucleation combined with domain wall pinning.The domain wall pinning is weakened,while the nucleation is enhanced after Pr-Cu addition.Theremanence,intrinsic coercivity,and maximum magnetic energy product of the original Nd-Fe-B magnet are 1.45 T,723 kA·m^(-1),and 419.8 kJ·m^(-3),respectively,and those of the sample with 4.0%Pr_(85)Cu_(15)alloy addition are 1.30 T,1271 kA·m^(-1),and 330.0 kJ·m^(-3),respectively.
基金financially supported by the National Key Research and Development Program of China(No.2018YFC1903405)Advanced Subject of Beijing+4 种基金China(No.PXM2019014204500031)the National Natural Science Foundation of China(Nos.5137100251331003 and 51201037)the 2011 Cooperative Innovation Center of Beijing University of Technologythe Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions。
文摘The coercivity,microstructure,and magnetic domain structure of Nd-Fe-B sintered magnets by grain boundary diffusion process(GBDP) with TbH3 nanoparticles were systematically investigated.Compared to the original magnet,the coercivity(Hci) of the GBDP magnets improved from 1702 to 2374 kA·m^(-1) with few remanence reduced from 1.338 to 1.281 T.Electron probe microanalysis(EPMA) analysis showed that Tb diffused along grain boundary,mainly concentrated in the boundary layer of the main phase,and formed a core-shell structure.Magneto-optical Kerr optical microscope(MOKE) analysis showed that there were two types of magnetic domain reversal in one grain:gradual reversal(GR) and abrupt reversal(AR).When the applied field decreased from saturated magnetic field,the reversal magnetic domain nucleated and then spread over the whole grain gradually,which was called GR.However,some grains kept the single domain state until Hh which was a value of reverse direction applied field in second quadrant in hysteresis loops.When the applied field increased above Hh,reversed magnetic domain would suddenly appear and occupy most of the area of the grain,which was called AR.That is because AR grains have higher reversed magnetic domain nucleation field(HRN2) than GR grains(HRN1).After GBDP,the area of AR region increased obviously and GR region decreased accordingly,indicating that the core-shell structure could change GR grain into AR grain.The coreshell structure could suppress flipping of the magnetization of the grains due to the large magnetic anisotropy of Tbrich shell.Therefore,large AR area led to high coercivity.
基金supported by Zhejiang Provincial Natural Science Foundation of China(No.LGC20E010004)the Science Foundation for Distinguished Young Scholars of Zhejiang Province(No.LR15E010001)+2 种基金the National Natural Science Foundation of China(No.51871205)the Key R&D Program of Zhejiang Province of China(No.2017C01004)the National Key Research and Development Project(No.2019YFF0217205)。
文摘In the present work,the magnetization reversal behavior for the melt spinning(Nd_(0.8)Ce_(0.2))_(2)Fe_(12)Co_(2-x)Zr_(x)B(x=0,0.5)permanent alloys with high coercivity was investigated by analyzing the hysteresis curves and the recoil loops.Compared to the Zr-free alloy,the Zr-doped sample obtains higher magnetic properties:coercivity of H_(cj)=650.5 kA·m^(-1),squareness of H_(k)/H_(cj)=0.76 and maximum energy product of(BH)_(max)=131.0 kJ·m^(-3).The first-order reversal curves(FORCs)analysis was taken to identify optimal conditions of exchange coupling for the Zr-free and Zr-doped alloys.The coercivity mechanism of theα-Fe/Nd_(2)Fe_(14)B nanocomposite alloys was analyzed by the angular dependence of the coercive field as measured for the Zr-doped sample.The results show that the magnetic reverse process of the Zr-doped sample can be explained by the pinning model.
基金financially supported by the National Natural Science Foundation of China(Nos.51871063,51571064 and 51590882)。
文摘Sm-Co permanent magnets are widely used in aerospace equipments,tubes,sensors and hybrid electric vehicles due to their excellent magnetic properties at both room and high temperatures.Compared to that of Nd-Fe-B magnets,the capability of reliably operating at temperatures up to 500℃ is the biggest preponderance of Sm-Co permanent magnets.However,the reliable high-temperature magnetic properties are susceptible to composition and technique processes.So,appropriate composition and matched technique processes are prerequisites for good high-temperature magnetic properties.This review mainly emphasizes the influences of Sm,Fe,Cu and Zr contents and technique processes on development of high-temperature performance and discusses the controversial hightemperature coercivity mechanism of 2:17-type high-temperature Sm-Co magnets.
基金Project supported by National Natural Science Foundation of China(51271070,51871087)the Natural Science Foundation of Hebei Province(E2016202406)。
文摘Highly ordered Tb_(x)Fe_(7)Co_(3)(x=0,0.6,0.8)nanowires were synthesized in alumina templates by electrochemical deposition method.Here,the effects of Tb content and annealing treatment on the phase composition,morphology,crystalline structure and magnetic properties were investigated.The asdeposited Tb_0 Fe_(7)Co_(3)nanowires comprise Fe_(7)Co_(3)phase.While after adding Tb,the diffraction peaks slightly shift left,indicating the infiltration of Tb atoms into Fe_(7)Co_(3)phase.After annealing,Tb_0 Fe_(7)Co_(3)nanowires still consist of Fe_(7)Co_(3)phase with a slight enhancement on coercivity.While the annealed nanowires with Tb doped present a complex phase composition containing Fe3 Tb,Fe_(2)Tb,Co_(3)Tb,Co_(17)Tb_(2),TbFeO_(3)and Fe_(2)O_(3)phases distribute in the central portion,and Co_(0.72)Fe_(0.28)at the nanowire outer walls.The annealed Tb_(x)Fe_(7)Co_(3)(x=0.6,0.8)nanowires show higher magnetic performance owing to the formation of hard magnetic phases,the interfacial elastic coupling between hard and soft phases and the coherent Fe3 Tb/Co_(3)Tb interface which restrain the domain wall motion.To be specific,the coercivity and remanence ratio of TbxFe_(7)Co_(3)(x=0.6,0.8)nanowires significantly enhance with increasing Tb content.