The intermetallic compounds based on the tetragonal ThMn_(12) prototype crystal structure have exhibited great potential as advanced rare-earth-lean permanent magnets due to their excellent intrinsic magnetic properti...The intermetallic compounds based on the tetragonal ThMn_(12) prototype crystal structure have exhibited great potential as advanced rare-earth-lean permanent magnets due to their excellent intrinsic magnetic properties.However,the trade-off between the phase stability and the magnetic performance is often encountered in the ThMn_(12)-type magnets.This work was focused on the effects of V doping and nanos-tructuring on the phase stability and magnetic properties of ThMn_(12)-type Sm-Co-based magnets.Novel SmCo_(12)-based nanocrystalline alloys with the SmCo_(12) main phase were prepared for the first time.The prepared alloys from the optimal design achieved obviously higher coercivity than the isotropic SmFe_(12)-based alloys,together with comparable performance of other magnetic features.The enhancement in the coercivity was ascribed to the pinning of domain walls by the nanocrystalline grain boundaries and stacking faults.First-principles calculations and magnetic structure analysis disclosed that V substitution can stabilize the SmCo_(12) lattice and elevate its magnetocrystalline anisotropy.This study provides a new approach to developing stabilized metastable structured rare-earth-lean alloys with high magnetic per-formance.展开更多
In this work, nanocrystalline SmCo_(5)-Cu nanocomposite powders were fabricated from the ball-milled amorphous matrix by crystallization annealing which is lower than the traditional sintering temperature ~ 1000℃ for...In this work, nanocrystalline SmCo_(5)-Cu nanocomposite powders were fabricated from the ball-milled amorphous matrix by crystallization annealing which is lower than the traditional sintering temperature ~ 1000℃ for bulk SmCo_(5) bulk magnets. Annealed Cu-doped SmCo_(5) powders have a higher coercivity compared to that of Cu-free SmCo_(5) one due to the combined effects of refinement effect of grain size and the pinning effect induced by Cu doping. The peak of coercivity (Hc) is located at 600℃ for annealed Cu-doped SmCo_(5), which is ascribed to the improved pinning field. The pinning effect became reduced when the annealing was done at even higher temperatures. More importantly, the best comprehensive magnetic properties, including a maximum magnetic energy product (BH)max of 12.2 MGOe together with a coercivity of 31.8 kOe and a remanence of 64.3 emu/g, could be achieved for SmCo_(5)-3 wt% Cu by low temperature annealing. These results demonstrate that isotropic Cu-doped SmCo_(5) nanocrystalline powders are promising precursors for the fabrication of high-performance bulk magnets.展开更多
Alloying with transition metal elements akin to Sm(CoFeCuZr)z can effectively enhance the magnetic properties of SmCo-based permanent magnets.However,the effects of transition metals doping on its magnetic properties,...Alloying with transition metal elements akin to Sm(CoFeCuZr)z can effectively enhance the magnetic properties of SmCo-based permanent magnets.However,the effects of transition metals doping on its magnetic properties,detailed atomic occupancy and the mechanism for structural stability remain unclear.Specifically,for SmCo3 magnets,there is minimal theoretical study available.Herein,based on first-principles calculations,we systematically investigated the influence of 3d transition metals(TMs)doping on the structural stability,magnetic properties and electronic characteristics of SmCo3 magnets.Our results show that Sc,Ti,V,Fe,Ni,Cu and Zn preferentially occupy the 18h lattice site,while Cr and Mn occupy the 3b and 6c lattice sites,respectively.Doping with Ti,Cr,Mn,Fe,Ni,Cu and Zn contributes to enhancing the stability of SmCo3,whereas the doping of Sc and V adversely affects structural stability.The magnetic calculations reveal that Cr,Mn and Fe doping significantly enhances the total magnetic moment.It is also found that lower concentrations of Cr doping can significantly enhance the magnetocrystalline anisotropy energy(MAE).More intriguingly,when the doping concentrations of Sc,Ni and Cu reach 14.81 at%,22.22 at%and 22.22 at%,respectively,the magnetic easy axis of the system shifts from out-of-plane to in-plane.The optimal doping concentration of Fe in the SmCo_(3) system is determined to be 37.04 at%.The Curie temperature of pure SmCo_(3) is 483.9 K.Our theoretical study offers valuable theoretical guidance for experimental exploration toward SmCo-based permanent magnets with higher performance.展开更多
SmConanoparticles(NPs) have promising applications in high-density magnetic storage and magnetic nanocomposites. In this work, A novel method to yield SmCoparticles with small size and high coercivity was reported. Fi...SmConanoparticles(NPs) have promising applications in high-density magnetic storage and magnetic nanocomposites. In this work, A novel method to yield SmCoparticles with small size and high coercivity was reported. Firstly, SmO-Co NPs with size of 6-15 nm were fabricated by a solvothermal route. Then the agglomerated SmCoparticles were obtained by thermal reduction of the precursor, which show high coercivity of2.0 T at room temperature. At last, the as-synthesized SmCoparticles were further hydrogenated under high hydrogen pressure of 4 MPa at room temperature, where hydrogen absorption process could form small-sized SmCoHparticles due to their lattice expansion and hydrogen desorption process could convert SmCoHNPs into SmCoNPs. The prepared SmCoNPs after hydrogenation, showing well distribution, have a small size of5-20 nm and room temperature coercivity of 1.22 T.展开更多
SmCo_(5)sintered magnets with good thermal stability are mainly used in high-temperature field.In this study,two types of SmCo_(5) powders with different nominal z values were mixed and synthesized into SmCo_(5) magne...SmCo_(5)sintered magnets with good thermal stability are mainly used in high-temperature field.In this study,two types of SmCo_(5) powders with different nominal z values were mixed and synthesized into SmCo_(5) magnets by the traditional powder metallurgy method.The magnetic properties of the SmCo_(5) sintered magnet are maximum energy product of(BH)_(max)=172.29 kJ·m^(-3),remanence of B_(r)=7.47×10^(5)A·m^(-1)and coercivity of H_(ci)=2.42 T.The results show that there are three coexisting phases in the magnet,which are SmCo_(5)phase,Sm_(2)Co_(7)phase and Sm_(2)O_(3)phase.The microstructural observation indicates that the average grain size in the magnet is about 8μm,and the high coercivity of this magnet is attributed to these fine grains.X-ray diffraction(XRD)and electron backscatter diffraction(EBSD)results indicate that the magnet has a well-aligned(00l)orientation texture.展开更多
A new strategy to chemically synthesize exchange-coupled SmCo_(5)/Sm_(2) Co_(17) nanocomposites by in situ decomposition of SmCox(5<x<8.5)is reported in this work.Our synthesis starts with the fabrication of Co/...A new strategy to chemically synthesize exchange-coupled SmCo_(5)/Sm_(2) Co_(17) nanocomposites by in situ decomposition of SmCox(5<x<8.5)is reported in this work.Our synthesis starts with the fabrication of Co/Sm_(2) O_(3)(Sm to Co atomic ratio of Sn/Co=1:4.2),which can be reduced into 40-nm SmCo_(5) single crystal nanoparticles by Ca under the protection of CaO,showing a high coercivity of 2.85 T and saturation magnetization(Ms)of 0.0671 A·m^(2)·g^(-1).By changing the Sm/Co to 1:4.5,1:4.8 and 1:5.2,SmCo_(5)/Sm_(2) Co_(17) nanocomposites with different proportions were acquired using the same process.Owing to the in situ decomposition of SmCo_(x) intermediate,the small size(both of their size less than 10 nm)and uniform phase distribution were achieved in our nanocomposites.Thus,the as-prepared nanocomposites display a strong exchange-coupling interaction.As a consequence,SMCo_(5)/Sm_(2)Co_(17)(Sm/Co=1:5.2)exhibits a coercivity of 1.23 T and enhanced M7 T(magnetization at 7 T)of 0.0812 A·m^(2)·g^(-1),increasing by 21%than pure SmCo_(5).Our synthesis provides a new protocol to prepare exchange-coupled high-performance nanocomposites.展开更多
SmCo_(5)alloy was prepared via direct calciothermic reduction using anhydrous samarium fluoride(SmF_(3))as raw material and cobalt as inducer.Results of the thermodynamic calculation show that the direct reduction of ...SmCo_(5)alloy was prepared via direct calciothermic reduction using anhydrous samarium fluoride(SmF_(3))as raw material and cobalt as inducer.Results of the thermodynamic calculation show that the direct reduction of cobalt-induced SmF_(3)for preparing SmCo_(5)alloy is feasible.An alloy with 33.89 wt%samarium and a yield of 96.45%were achieved under the optimal conditions of 10%and 20%excess of SmF_(3)and calcium over the stoichiometry,respectively,and 1450℃for 4 min.The X-ray diffraction results show that the reduction products are SmCo_(5)alloy and CaF_(2).The scanning electron microscopy micrograph of the SmCo_(5)alloy ingot exhibits a distinct dendritic morphology composed of samarium and cobalt.The X-ray photoelectron spectroscopy shows that the atomic ratio of samarium to cobalt is approximately 1:5 and both elements demonstrate zero valency(Sm^(0),Co^(0)).The magnetic properties measurement of the SmCo_(5)alloy melt-spun ribbon shows the remanent magnetization B_r=0.59 T,intrinsic coercivity H_(Ci)=345.82 kA/m and maximum magnetic energy density(BH)_(max)=42.20 kJ/m^(3).These results may be helpful for the development of novel valence-variable rare-earth alloys.展开更多
The application of ‘extreme’ hydrogen-decrepitation (HD) process using high-pressure disproportionation was extended to Sm-Co5-type-alloy. The alloy with nominal composition of Sm36Co64 was treated under 1.0～2.0 MP...The application of ‘extreme’ hydrogen-decrepitation (HD) process using high-pressure disproportionation was extended to Sm-Co5-type-alloy. The alloy with nominal composition of Sm36Co64 was treated under 1.0～2.0 MPa H2 pressure for several hours at room temperature for decrepitation. After disproportionation were high hydrogen pressures, the bulk alloys were disproportionated into particles with a size of 200. Investigations by powder X-ray diffractometer (XRD) showed, the after HD sample crystallized in the hexagonal CaCu5-type structure. The temperature dependence of pressure analysis (TPA) curve of the SmCo5 alloy showed that the hydrogen absorption temperature was about 150 ℃. Cylindrical sintered magnets of composition Sm36Co64 were prepared using HD ball milled, isostatic pressing, vacuum sintering and subsequent heat treatment. The demagnetization curves showed that the HD processes could improve the magnetic properties and squareness factor of the SmCo5 sintered magnet.展开更多
Magnetic properties and microstructure of SmCo_5 alloys were examined. It is found that the coercivity ofthe alloy is strongly influenced by its microstructure. If more non- 1 : 5 phase precipitated particles wereform...Magnetic properties and microstructure of SmCo_5 alloys were examined. It is found that the coercivity ofthe alloy is strongly influenced by its microstructure. If more non- 1 : 5 phase precipitated particles wereformed, which are properly due to the existing of oxygen in the alloys introduced during the heat treatment process, the magnetic properties of the alloy decrease.展开更多
The relation between the tempering effects of sinterd SmCo^(5)alloy at 750℃and its intrinsic coercivity(i^(Hc))has been studied by the use of photoelectron energy spectrum.X-ray diffraction and high-voltage electron ...The relation between the tempering effects of sinterd SmCo^(5)alloy at 750℃and its intrinsic coercivity(i^(Hc))has been studied by the use of photoelectron energy spectrum.X-ray diffraction and high-voltage electron microscope.The result is that the cause of iHc dropping seriously for sintered SmCo_(5)alloy tempered at 750 t is not the eutectoid decomposition of SmCo_(5)and the increase of oxygen.In fact,iHcdropping is caused by that some defect-rich regions in Sm_(2)Co_(17)decomposed form SmC0_(5)from nucleation centers in reversed magnetization course.展开更多
基金supported by the National Key R&D Program of China(Nos.2021YFB3501502 and 2021YFB3501504).
文摘The intermetallic compounds based on the tetragonal ThMn_(12) prototype crystal structure have exhibited great potential as advanced rare-earth-lean permanent magnets due to their excellent intrinsic magnetic properties.However,the trade-off between the phase stability and the magnetic performance is often encountered in the ThMn_(12)-type magnets.This work was focused on the effects of V doping and nanos-tructuring on the phase stability and magnetic properties of ThMn_(12)-type Sm-Co-based magnets.Novel SmCo_(12)-based nanocrystalline alloys with the SmCo_(12) main phase were prepared for the first time.The prepared alloys from the optimal design achieved obviously higher coercivity than the isotropic SmFe_(12)-based alloys,together with comparable performance of other magnetic features.The enhancement in the coercivity was ascribed to the pinning of domain walls by the nanocrystalline grain boundaries and stacking faults.First-principles calculations and magnetic structure analysis disclosed that V substitution can stabilize the SmCo_(12) lattice and elevate its magnetocrystalline anisotropy.This study provides a new approach to developing stabilized metastable structured rare-earth-lean alloys with high magnetic per-formance.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFB3507600)the National Natural Science Foundation of China(Nos.U23A20549 and 52171184).
文摘In this work, nanocrystalline SmCo_(5)-Cu nanocomposite powders were fabricated from the ball-milled amorphous matrix by crystallization annealing which is lower than the traditional sintering temperature ~ 1000℃ for bulk SmCo_(5) bulk magnets. Annealed Cu-doped SmCo_(5) powders have a higher coercivity compared to that of Cu-free SmCo_(5) one due to the combined effects of refinement effect of grain size and the pinning effect induced by Cu doping. The peak of coercivity (Hc) is located at 600℃ for annealed Cu-doped SmCo_(5), which is ascribed to the improved pinning field. The pinning effect became reduced when the annealing was done at even higher temperatures. More importantly, the best comprehensive magnetic properties, including a maximum magnetic energy product (BH)max of 12.2 MGOe together with a coercivity of 31.8 kOe and a remanence of 64.3 emu/g, could be achieved for SmCo_(5)-3 wt% Cu by low temperature annealing. These results demonstrate that isotropic Cu-doped SmCo_(5) nanocrystalline powders are promising precursors for the fabrication of high-performance bulk magnets.
基金supported by the National Key Research and Development Program of China(No.2022YFB3505301)the National Key Research and Development Program of Shanxi Province(No.202302050201014)+2 种基金the National Natural Science Foundation of China(No.12304148)the Natural Science Basic Research Program of Shanxi Province(No.202203021222219)the China Postdoctoral Science Foundation(No.2023M731452).
文摘Alloying with transition metal elements akin to Sm(CoFeCuZr)z can effectively enhance the magnetic properties of SmCo-based permanent magnets.However,the effects of transition metals doping on its magnetic properties,detailed atomic occupancy and the mechanism for structural stability remain unclear.Specifically,for SmCo3 magnets,there is minimal theoretical study available.Herein,based on first-principles calculations,we systematically investigated the influence of 3d transition metals(TMs)doping on the structural stability,magnetic properties and electronic characteristics of SmCo3 magnets.Our results show that Sc,Ti,V,Fe,Ni,Cu and Zn preferentially occupy the 18h lattice site,while Cr and Mn occupy the 3b and 6c lattice sites,respectively.Doping with Ti,Cr,Mn,Fe,Ni,Cu and Zn contributes to enhancing the stability of SmCo3,whereas the doping of Sc and V adversely affects structural stability.The magnetic calculations reveal that Cr,Mn and Fe doping significantly enhances the total magnetic moment.It is also found that lower concentrations of Cr doping can significantly enhance the magnetocrystalline anisotropy energy(MAE).More intriguingly,when the doping concentrations of Sc,Ni and Cu reach 14.81 at%,22.22 at%and 22.22 at%,respectively,the magnetic easy axis of the system shifts from out-of-plane to in-plane.The optimal doping concentration of Fe in the SmCo_(3) system is determined to be 37.04 at%.The Curie temperature of pure SmCo_(3) is 483.9 K.Our theoretical study offers valuable theoretical guidance for experimental exploration toward SmCo-based permanent magnets with higher performance.
基金financially supported by the National Natural Science Foundations of China (Nos. 51471016 and 51520105002)the Key Natural Science Foundation of Beijing (No. 2151002)
文摘SmConanoparticles(NPs) have promising applications in high-density magnetic storage and magnetic nanocomposites. In this work, A novel method to yield SmCoparticles with small size and high coercivity was reported. Firstly, SmO-Co NPs with size of 6-15 nm were fabricated by a solvothermal route. Then the agglomerated SmCoparticles were obtained by thermal reduction of the precursor, which show high coercivity of2.0 T at room temperature. At last, the as-synthesized SmCoparticles were further hydrogenated under high hydrogen pressure of 4 MPa at room temperature, where hydrogen absorption process could form small-sized SmCoHparticles due to their lattice expansion and hydrogen desorption process could convert SmCoHNPs into SmCoNPs. The prepared SmCoNPs after hydrogenation, showing well distribution, have a small size of5-20 nm and room temperature coercivity of 1.22 T.
基金the State Key Program of Natural Science Foundation of China(No.51331003)the International S&T Cooperation Program of China(No.2015DFG52020)。
文摘SmCo_(5)sintered magnets with good thermal stability are mainly used in high-temperature field.In this study,two types of SmCo_(5) powders with different nominal z values were mixed and synthesized into SmCo_(5) magnets by the traditional powder metallurgy method.The magnetic properties of the SmCo_(5) sintered magnet are maximum energy product of(BH)_(max)=172.29 kJ·m^(-3),remanence of B_(r)=7.47×10^(5)A·m^(-1)and coercivity of H_(ci)=2.42 T.The results show that there are three coexisting phases in the magnet,which are SmCo_(5)phase,Sm_(2)Co_(7)phase and Sm_(2)O_(3)phase.The microstructural observation indicates that the average grain size in the magnet is about 8μm,and the high coercivity of this magnet is attributed to these fine grains.X-ray diffraction(XRD)and electron backscatter diffraction(EBSD)results indicate that the magnet has a well-aligned(00l)orientation texture.
基金This study was financially supported by the National Natural Science Foundation of China(No.51701109)the Natural Science Foundation of Beijing Municipality,China(No.2192007)+1 种基金the China Postdoctoral Science Foundation(No.2018M641132)Leshan Normal University Research Program,China(No.LZD021).
文摘A new strategy to chemically synthesize exchange-coupled SmCo_(5)/Sm_(2) Co_(17) nanocomposites by in situ decomposition of SmCox(5<x<8.5)is reported in this work.Our synthesis starts with the fabrication of Co/Sm_(2) O_(3)(Sm to Co atomic ratio of Sn/Co=1:4.2),which can be reduced into 40-nm SmCo_(5) single crystal nanoparticles by Ca under the protection of CaO,showing a high coercivity of 2.85 T and saturation magnetization(Ms)of 0.0671 A·m^(2)·g^(-1).By changing the Sm/Co to 1:4.5,1:4.8 and 1:5.2,SmCo_(5)/Sm_(2) Co_(17) nanocomposites with different proportions were acquired using the same process.Owing to the in situ decomposition of SmCo_(x) intermediate,the small size(both of their size less than 10 nm)and uniform phase distribution were achieved in our nanocomposites.Thus,the as-prepared nanocomposites display a strong exchange-coupling interaction.As a consequence,SMCo_(5)/Sm_(2)Co_(17)(Sm/Co=1:5.2)exhibits a coercivity of 1.23 T and enhanced M7 T(magnetization at 7 T)of 0.0812 A·m^(2)·g^(-1),increasing by 21%than pure SmCo_(5).Our synthesis provides a new protocol to prepare exchange-coupled high-performance nanocomposites.
基金Project supported by the National Natural Science Foundation of China(NSFC)(51774155)Jiangxi Provincial Key Research and Development Program(20192BBE50028)the Doctoral Scientific Research Foundation of Jiangxi University of Science and Technology(jxxjbs17077)。
文摘SmCo_(5)alloy was prepared via direct calciothermic reduction using anhydrous samarium fluoride(SmF_(3))as raw material and cobalt as inducer.Results of the thermodynamic calculation show that the direct reduction of cobalt-induced SmF_(3)for preparing SmCo_(5)alloy is feasible.An alloy with 33.89 wt%samarium and a yield of 96.45%were achieved under the optimal conditions of 10%and 20%excess of SmF_(3)and calcium over the stoichiometry,respectively,and 1450℃for 4 min.The X-ray diffraction results show that the reduction products are SmCo_(5)alloy and CaF_(2).The scanning electron microscopy micrograph of the SmCo_(5)alloy ingot exhibits a distinct dendritic morphology composed of samarium and cobalt.The X-ray photoelectron spectroscopy shows that the atomic ratio of samarium to cobalt is approximately 1:5 and both elements demonstrate zero valency(Sm^(0),Co^(0)).The magnetic properties measurement of the SmCo_(5)alloy melt-spun ribbon shows the remanent magnetization B_r=0.59 T,intrinsic coercivity H_(Ci)=345.82 kA/m and maximum magnetic energy density(BH)_(max)=42.20 kJ/m^(3).These results may be helpful for the development of novel valence-variable rare-earth alloys.
基金the National Natural Science Foundation of ChinaBeijing Municipal Science &Technology Commission for financial support for the study
文摘The application of ‘extreme’ hydrogen-decrepitation (HD) process using high-pressure disproportionation was extended to Sm-Co5-type-alloy. The alloy with nominal composition of Sm36Co64 was treated under 1.0～2.0 MPa H2 pressure for several hours at room temperature for decrepitation. After disproportionation were high hydrogen pressures, the bulk alloys were disproportionated into particles with a size of 200. Investigations by powder X-ray diffractometer (XRD) showed, the after HD sample crystallized in the hexagonal CaCu5-type structure. The temperature dependence of pressure analysis (TPA) curve of the SmCo5 alloy showed that the hydrogen absorption temperature was about 150 ℃. Cylindrical sintered magnets of composition Sm36Co64 were prepared using HD ball milled, isostatic pressing, vacuum sintering and subsequent heat treatment. The demagnetization curves showed that the HD processes could improve the magnetic properties and squareness factor of the SmCo5 sintered magnet.
文摘Magnetic properties and microstructure of SmCo_5 alloys were examined. It is found that the coercivity ofthe alloy is strongly influenced by its microstructure. If more non- 1 : 5 phase precipitated particles wereformed, which are properly due to the existing of oxygen in the alloys introduced during the heat treatment process, the magnetic properties of the alloy decrease.
文摘The relation between the tempering effects of sinterd SmCo^(5)alloy at 750℃and its intrinsic coercivity(i^(Hc))has been studied by the use of photoelectron energy spectrum.X-ray diffraction and high-voltage electron microscope.The result is that the cause of iHc dropping seriously for sintered SmCo_(5)alloy tempered at 750 t is not the eutectoid decomposition of SmCo_(5)and the increase of oxygen.In fact,iHcdropping is caused by that some defect-rich regions in Sm_(2)Co_(17)decomposed form SmC0_(5)from nucleation centers in reversed magnetization course.
