The phase structure and magnetic properties of high-Co containing permanent magnets with high thermal stability have been systematically studied in this work.It is abnormal that the coercivity of annealed samples was ...The phase structure and magnetic properties of high-Co containing permanent magnets with high thermal stability have been systematically studied in this work.It is abnormal that the coercivity of annealed samples was slightly lower than that of sintered samples,while the coercivity was usually enhanced after annealing in conventional Nd–Fe–B samples.Further analysis showed that in addition to RE_(2)(Fe,Co)_(14)B main phase and RE-rich grain boundary phase,there were also new Co-rich magnetic phases located in the grain boundary.During annealing,the phase structures of high-Co containing magnets were readjusted,especially the increasing Co-rich magnetic phase and emerging RE-rich particles precipitated from the main phase.Eventually,the isolated RE-rich particles would act as the pinning center of the domain wall movement in demagnetization process.It was confirmed that the coercivity of annealed high-Co containing magnets was controlled by both nucleation and pinning.Pinning mechanism can partially compensate for the weakening of magnetic isolation due to increased Co-rich magnetic phase,which explained the moderate decrease in coercivity of annealed high-Co containing magnets.The discovery of new coercivity mechanism contributed to in-depth understanding of high-Co containing magnets.展开更多
This study investigated the effect of antioxidants on the grinding efficiency,magnetic powder characteristics,microstructure,and magnetic properties of 2:17 type SmCo permanent magnet materials.The results show that a...This study investigated the effect of antioxidants on the grinding efficiency,magnetic powder characteristics,microstructure,and magnetic properties of 2:17 type SmCo permanent magnet materials.The results show that adding antioxidants helps improve the dispersion among magnetic powders,leading to a 33.3%decrease in jet milling time and a 15.8%increase in magnet powder production yield.Additionally,adding antioxidants enhances the oxidation resistance of the magnetic powders.After being stored in a constant temperature air environment at 25C for 48 h,the O content in the powder decreased by 33%compared to samples without antioxidants.While in the magnet body,the O content decreased from 0.21 wt.%to 0.14 wt.%,which helps increase the effective Sm content and domain wall pinning uniformity in the magnet.Excellent magnetic properties were obtained in the magnet with added antioxidants:B_(r)=11.6 kGs,SF=79.6%,H_(cj)=16.8 kOe,and(BH)_(max)=32.5 MGOe.展开更多
The effects of Nd doping on the microstructures and magnetic properties of Sm_(1-x)Nd_(x)(Co_(0.695)Fe_(0.2)Cu_(0.08)Zr_(0.025))7.2(x = 0, 0.3, 0.5, 0.7, 1.0) permanent magnets are studied. The scanning electron micro...The effects of Nd doping on the microstructures and magnetic properties of Sm_(1-x)Nd_(x)(Co_(0.695)Fe_(0.2)Cu_(0.08)Zr_(0.025))7.2(x = 0, 0.3, 0.5, 0.7, 1.0) permanent magnets are studied. The scanning electron microscope(SEM) analysis of the solid solution states of the magnets shows that with the increase of Nd content, the distribution of elements becomes inhomogeneous and miscellaneous phase will be generated. Positive temperature coefficient of coercivity(β) appears in each of the samples with x = 0.3, 0.5, and 0.7. The corresponding positive β temperatures are in ranges of about 70 K–170 K,60 K–260 K, 182 K–490 K for the samples with x = 0.3, 0.5, and 0.7, respectively. Thermomagnetic analysis shows that spin-reorientation-transition(SRT) of the cell boundary phase is responsible for this phenomenon. On the basis of this discovery, the Sm_(0.7)Nd_(0.3)(Co_(0.695)Fe_(0.2)Cu_(0.08)Zr_(0.025))7.2magnet possessing thermal stability with β ≈-0.002 %/K at the temperature in a range of 150 K–200 K is obtained.展开更多
Four Sm_(2)Co_(17)magnets with spin-reorientation transition(SRT)of cell boundary phases(CBPs)are prepared by liquid-phase sintering.The temperature of the SRT of CBPs(T_(SR)^(1:5))is regulated from 125 K to 195 K by ...Four Sm_(2)Co_(17)magnets with spin-reorientation transition(SRT)of cell boundary phases(CBPs)are prepared by liquid-phase sintering.The temperature of the SRT of CBPs(T_(SR)^(1:5))is regulated from 125 K to 195 K by adding 0 wt.%,3 wt.%,6 wt.%and 9 wt.%Dy_(88)Cu_(12)alloy powder.The effect of SRT of Sm_(2)Co_(17)magnet CBPs on the temperature dependence of the magnetization(M-T)and coercivity(H-T)is systematically investigated.The temperature dependence of the magnetization is influenced by the SRT of CBPs.The M-T curves measured during the heating process are larger than those measured during the cooling process when T<T_(SR)^(1:5).When T=T_(SR)^(1:5)there is a bifurcation point.When T>T_(SR)^(1:5)the M-T curves overlap and the M-T derivation curve shows that the magnetization of the magnet has low temperature dependence of magnetization above T_(SR)^(1:5).With increasing T_(SR)^(1:5),the initial temperature of the low temperature dependence of magnetization shifts towards a higher temperature.The coercivity temperature coefficient becomes positive as the SRT effect increases,and the temperature range of the positive coercivity temperature coefficient moves towards higher temperatures as T_(SR)^(1:5)increases.This reveals that SRT of CBPs has little effect on the temperature dependence of magnetization above T_(SR)^(1:5),while the temperature dependence of coercivity is optimized.The temperature range of magnetization and coercivity with low temperature dependence tends towards higher temperatures,which is conducive to the preparation of magnets with a low temperature coefficient at higher temperatures.展开更多
基金Project supported by National Key R&D Program of China(Grant No.2021YFB3803003)Youth Innovation Promotion Association CAS(Grant No.2023311).
文摘The phase structure and magnetic properties of high-Co containing permanent magnets with high thermal stability have been systematically studied in this work.It is abnormal that the coercivity of annealed samples was slightly lower than that of sintered samples,while the coercivity was usually enhanced after annealing in conventional Nd–Fe–B samples.Further analysis showed that in addition to RE_(2)(Fe,Co)_(14)B main phase and RE-rich grain boundary phase,there were also new Co-rich magnetic phases located in the grain boundary.During annealing,the phase structures of high-Co containing magnets were readjusted,especially the increasing Co-rich magnetic phase and emerging RE-rich particles precipitated from the main phase.Eventually,the isolated RE-rich particles would act as the pinning center of the domain wall movement in demagnetization process.It was confirmed that the coercivity of annealed high-Co containing magnets was controlled by both nucleation and pinning.Pinning mechanism can partially compensate for the weakening of magnetic isolation due to increased Co-rich magnetic phase,which explained the moderate decrease in coercivity of annealed high-Co containing magnets.The discovery of new coercivity mechanism contributed to in-depth understanding of high-Co containing magnets.
基金the National Key R&D Program of China(Grant No.2021YFB3803003)the Youth Innova-tion Promotion Association of Chinese Academy of Sciences(Grant No.2023311)+1 种基金Zhejiang Public Welfare Technology Application Research Project(Grant No.LGG22E010013)Class III Peak Discipline of Shanghai-Materials Science and Engineering(High-Energy Beam Intelligent Processing and Green Manufacturing).
文摘This study investigated the effect of antioxidants on the grinding efficiency,magnetic powder characteristics,microstructure,and magnetic properties of 2:17 type SmCo permanent magnet materials.The results show that adding antioxidants helps improve the dispersion among magnetic powders,leading to a 33.3%decrease in jet milling time and a 15.8%increase in magnet powder production yield.Additionally,adding antioxidants enhances the oxidation resistance of the magnetic powders.After being stored in a constant temperature air environment at 25C for 48 h,the O content in the powder decreased by 33%compared to samples without antioxidants.While in the magnet body,the O content decreased from 0.21 wt.%to 0.14 wt.%,which helps increase the effective Sm content and domain wall pinning uniformity in the magnet.Excellent magnetic properties were obtained in the magnet with added antioxidants:B_(r)=11.6 kGs,SF=79.6%,H_(cj)=16.8 kOe,and(BH)_(max)=32.5 MGOe.
基金supported by the National Key Research and Development Program of China (Grant Nos. 2021YFB3803003 and 2021YFB3503101)the Major Project of “Science and Technology Innovation 2025” in Ningbo, China (Grant No. 2020Z044)+1 种基金the Zhejiang Provincial Key Research and Development Program, China (Grant No. 2021C01172)the National Natural Science Funds of China (Grant No. 51601209)。
文摘The effects of Nd doping on the microstructures and magnetic properties of Sm_(1-x)Nd_(x)(Co_(0.695)Fe_(0.2)Cu_(0.08)Zr_(0.025))7.2(x = 0, 0.3, 0.5, 0.7, 1.0) permanent magnets are studied. The scanning electron microscope(SEM) analysis of the solid solution states of the magnets shows that with the increase of Nd content, the distribution of elements becomes inhomogeneous and miscellaneous phase will be generated. Positive temperature coefficient of coercivity(β) appears in each of the samples with x = 0.3, 0.5, and 0.7. The corresponding positive β temperatures are in ranges of about 70 K–170 K,60 K–260 K, 182 K–490 K for the samples with x = 0.3, 0.5, and 0.7, respectively. Thermomagnetic analysis shows that spin-reorientation-transition(SRT) of the cell boundary phase is responsible for this phenomenon. On the basis of this discovery, the Sm_(0.7)Nd_(0.3)(Co_(0.695)Fe_(0.2)Cu_(0.08)Zr_(0.025))7.2magnet possessing thermal stability with β ≈-0.002 %/K at the temperature in a range of 150 K–200 K is obtained.
基金Project supported by the National Key R&D Program of China (Grant Nos.2021YFB3803003 and 2021YFB3503101)Youth Innovation Promotion Association of CAS (Grant No.2023311)+1 种基金Major Project of‘Science and Technology Innovation 2025’in Ningbo (Grant No.2020Z044)Zhejiang Provincial Key Research and Development Program (Grant No.2021C01172)。
文摘Four Sm_(2)Co_(17)magnets with spin-reorientation transition(SRT)of cell boundary phases(CBPs)are prepared by liquid-phase sintering.The temperature of the SRT of CBPs(T_(SR)^(1:5))is regulated from 125 K to 195 K by adding 0 wt.%,3 wt.%,6 wt.%and 9 wt.%Dy_(88)Cu_(12)alloy powder.The effect of SRT of Sm_(2)Co_(17)magnet CBPs on the temperature dependence of the magnetization(M-T)and coercivity(H-T)is systematically investigated.The temperature dependence of the magnetization is influenced by the SRT of CBPs.The M-T curves measured during the heating process are larger than those measured during the cooling process when T<T_(SR)^(1:5).When T=T_(SR)^(1:5)there is a bifurcation point.When T>T_(SR)^(1:5)the M-T curves overlap and the M-T derivation curve shows that the magnetization of the magnet has low temperature dependence of magnetization above T_(SR)^(1:5).With increasing T_(SR)^(1:5),the initial temperature of the low temperature dependence of magnetization shifts towards a higher temperature.The coercivity temperature coefficient becomes positive as the SRT effect increases,and the temperature range of the positive coercivity temperature coefficient moves towards higher temperatures as T_(SR)^(1:5)increases.This reveals that SRT of CBPs has little effect on the temperature dependence of magnetization above T_(SR)^(1:5),while the temperature dependence of coercivity is optimized.The temperature range of magnetization and coercivity with low temperature dependence tends towards higher temperatures,which is conducive to the preparation of magnets with a low temperature coefficient at higher temperatures.
