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Frontiers of Materials Science 2019年第3期13卷 323-333页

作者： Wei LI lizhong zhao Zhongwu LIU School of Materials Science and Engineering South China University of TechnologyGuangzhou 510640China Innovative Center for Advanced Materials Hangzhou Dianzi UniversityHangzhou 310012China

A simplified analysis method based on micromagnetic simulation is proposed to investigate effects of nonmagnetic particles on the demagnetizing field of a permanent magnet By applying the additivity law of the demagnetizing field,the complicated demagnetizing field of the real magnet could be analyzed by only focusing on the stray field of the reserved magnet For a magnet with nonmagnetic particles inside,the particle size has no significant effect on the maximum value of the demagnetization field,but the area of the affected region by the particle is proportional to the particle size.A large particle produces a large affected area overlapped with those influenced by other particles,which leads to the large demagnetization *** increasing the length of the particle along the magnetization direction,the demagnetization field on the pole surface *** pole surface with a convex shape will increase the demagnetization *** demagnetizing field near the nonmagnetic particle will be further increased by the large macroscopic demagnetizing field near the pole *** work suggests some practical approaches to optimize the microstructure of permanent magnets.

关键词： demagnetizing field additivity micromagnetic simulation nonmagneticphase nucleation process

Micromagnetic simulation on magnetic properties of Nd2Fe14B/α-Fe nanocomposites with Fe nanowires as the soft phase

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Frontiers of Materials Science 2018年第4期12卷 348-353页

作者： Wei LI lizhong zhao Zhongwu LIU School of Materials Science and Engineering South China University of TechnologyGuangzhou 510640China

Fe nanowire array with strong shape anisotropy was employed as the soft phase in Nd-Fe-B based nanocomposites. The effects of the Fe nanowire distribution on magnetic properties of the nanocomposites were investigated by micromagnetic simulation. The results indicate that the shape anisotropy of Fe wires added in the same direction as the uniaxial magnetocrystalline anisotropy of the hard phase cannot increase the coercivity of the nanocomposite. When the nanowires are distributed perpendicular to the easy axis of the hard phase, the shape anisotropy of soft phase can retard the moments from rotating to the full reversed direction, leading to enhanced coercivity. In addition, with increasing the nanowire diameter, the coercivity of the nanocomposite decreases, but the dipolar interaction shows different roles in magnetic reversal of nanocomposite for different distributions of nanowires. The current results suggest that the coercivity of the Nd2Fe14B/α-Fe nanocomposite can be enhanced by introducing the soft magnetic nanowire array with the diameter less than the exchange length and with the long axis along the direction other than the easy axis of hard phase.

关键词： Nd2Fe14B/α-Fe nanocomposite micromagnetic simulation Fe nanowires shape anisotropy exchange coupling

Enhanced magnetic properties in chemically inhomogeneous Nd-Dy-Fe-B sintered magnets by multi-main-phase process

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Journal of Rare Earths 2021年第5期39卷 558-564页

作者： Xiaolian Liu Mengjie Pan Pei Zhang Tianyu Ma lizhong zhao Lingwei Li College of Materials&Environmental Engineering Hangzhou Dianzi UniversityHangzhou 310018China State Key Laboratory of Silicon Materials Key Laboratory of Novel Materials for Information Technology of Zhejiang ProvinceDepartment of Materials Science and EngineeringZhejiang UniversityHangzhou 310027China

Homogeneous substitution of Dy for Nd in the hard magnetic 2:14:1 phase can effectively enhance coercivity to ensure the high temperature operation,however,inevitably deteriorate remanence at *** this work,we performed a comparative investigation of the two magnets prepared by multimain-phase(co-sintering Nd_(2)Fe_(14)B and(Nd,Dy)_(2)Fe_(14)B powders)and single-main-phase(sintering(Nd,Dy)_(2)Fe_(14)B powders)*** comparative investigation reveals that at the same Dy substitution level(2.16 wt%),such chemically inhomogeneous multi-main-phase magnet possesses better roomtemperature magnetic properties as well as thermal stability than those of the single-main-phase one with homogenous Dy distribution in the matrix ***-temperature magnetic properties H_(Cj)=1664 kA/m,B_(r)=1.33 T and(BH)_(max)=350.4 kJ/m^(3)for the multi-main-phase magnet are all better than those for the single-main-phase magnet with H_(Cj)=1536 kA/m,B_(r)=1.29 T and(BH)_(max)=318.4 kj/m^(3).In addition,over the temperature range from 295 to 423 K,both the temperature coefficients of coercivity and remanence for the multi-main-phase magnet are also lower than that for the single-main-phase *** superior magnetic performance is attributed to the short-range magnetic interactions inside individual 2:14:1 phase grains and the long-range magnetostatic interactions between adjacent grains with inhomogeneous Dy *** work provides a feasible approach of enhancing coercivity and retaining energy product simultaneously in the Nd-Dy-Fe-B permanent magnets.

关键词： Permanent magnet Nd-Fe-B magnet Multi-main-phase Magnetic properties Thermal stability Microstructure

A microcosmic discrete occupant evacuation model based on individual characteristics

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Science China(Technological Sciences) 2004年第5期47卷 608-615页

作者： YANG lizhong LI Jian zhao Daoliang FANG Weifeng FAN Weicheng State Key Laboratory of Fire Science University of Science and Technology of China Hefei 230026 China State Key Laboratory of Fire Science University of Science and Technology of China Hefei 230026 China State Key Laboratory of Fire Science University of Science and Technology of China Hefei 230026 China State Key Laboratory of Fire Science University of Science and Technology of China Hefei 230026 China State Key Laboratory of Fire Science University of Science and Technology of China Hefei 230026 China

The research of occupant evacuation in an emergency is of great benefit to building design and evacuation guidance. In this paper a microcosmic discrete evacuation model based on Cellular Automata (CA) is presented, in which the occupants?individual characteristics are considered. Thus, our model has given a description of evacuation route choice with influencing factors, including: individual knowledge of the building, individual realization of the emergency development, and the attractive and repulsive force between occupants. This model differs somewhat from other models in the attention to the associative and separate effect of influencing factors, based on occupants behaviors. In addition, the model could reveal the phenomenon of escape in fire, as those simulations involving a fire condition have shown.

关键词： evacuation, cellular automata, microcosmic discrete model, occupant behavior, fire.

Influence of gadolinium and dysprosium substitution on magnetic properties and magnetocaloric effect of Fe78-xRExSi4Nb5B12Cu1 amorphous alloys

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Journal of Rare Earths 2020年第12期38卷 1317-1321页

作者： lizhong zhao Huacun Tian Xichun Zhong Zhongwu Liu Jean-Marc Greneche R.V.Ramanujan Institute of Advanced Magnetic Materials Hangzhou Dianzi UniversityHangzhou 310012China School of Materials Science and Engineering South China University of TechnologyGuangzhou 510640China Guangdong Institute of Special Equipment Inspection and Research Guangzhou 528251China Institut des Molecules et Materiaux du Mans UMR CNRS 6283 Le Mans UniversiteAvenue MessiaenLe MansF-72085France School of Materials Science and Engineering Nanyang Technological University639798Singapore Singapore-HUJ Alliance for Research and Enterprise(SHARE) Nanomaterials for Energy and Energy-Water Nexus(NEW)Campus for Research Excellence and Technological Enterprise(CREATE)Singapore138602Singapore

Amorphous Fe78-xRExSi4 Nb5 B12Cu1(RE=Gd,Dy) ribbons with different RE contents were prepared by melt spinning to investigate the effect of heavy rare earth(Gd,Dy) substitution on the hyperfine structure,magnetic properties and magnetocaloric *** Curie temperature of RE substituted alloys,hyperfine field and magnetic moments of Fe atoms initially increase up to 1 at% RE content and then decrease monotonously for increasing RE content up to 10 at%.The dependence of magnetic entropy change(-△SM) and refrigeration capacity(RC) of the alloys on RE contents displays the same *** RCAREA values of the alloys substituted with 1 at% Gd and Dy are similar to those of recently reported Fe-based metallic glasses with enhanced RC values compared with those of Gd5 Ge1.9Si2 ***-△SM and RC values,negligible coercive force and hysteresis commonly make these Fe78-xREx-Si4 Nb5 B12Cu1 amorphous alloys as low-cost candidates for high-temperature magnetic refrigeration.

关键词： Magnetic properties Magnetocaloric effect Refrigeration capacity Rare earths

High-entropy-alloy nanoparticles with 21 ultra-mixed elements for efficient photothermal conversion

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National Science Review 2022年第6期9卷 124-134页

作者： Yijun Liao Yixing Li Rongzhi zhao Jian Zhang lizhong zhao Lianze Ji Zhengyu Zhang Xiaolian Liu Gaowu Qin Xuefeng Zhang Key Laboratory for Anisotropy and Texture of Materials (MOE) School of Materials Science and EngineeringNortheastern University Institute of Advanced Magnetic Materials College of Materials and Environmental EngineeringHangzhou Dianzi University

Multi-metallic nanoparticles have been proven to be an efficient photothermal conversion material, for which the optical absorption can be broadened through the interband transitions(IBTs), but it remains a challenge due to the strong immiscibility among the repelling combinations. Here, assisted by an extremely high evaporation temperature, ultra-fast cooling and vapor-pressure strategy, the arc-discharged plasma method was employed to synthesize ultra-mixed multi-metallic nanoparticles composed of 21 elements(FeCoNiCrYTiVCuAlNbMoTaWZnCdPbBiAgInMnSn), in which the strongly repelling combinations were uniformly distributed. Due to the reinforced lattice distortion effect and excellent IBTs, the nanoparticles can realize an average absorption of >92% in the entire solar spectrum(250 to 2500 nm). In particular, the 21-element nanoparticles achieve a considerably high solar steam efficiency of nearly 99%under one solar irradiation, with a water evaporation rate of 2.42 kg m-2h-1, demonstrating a highly efficient photothermal conversion performance. The present approach creates a new strategy for uniformly mixing multi-metallic elements for exploring their unknown properties and various applications.

关键词： high-entropy alloy nanoparticle ultra-mixing arc-discharged method photothermal conversion

Microstructure improvement related coercivity enhancement for sintered NdFeB magnets after optimized additional heat treatment

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Journal of Rare Earths 2018年第4期36卷 379-384页

作者： Qing Zhou Wei Li Yuan Hong lizhong zhao Xichun Zhong Hongya Yu Lili Huang Zhongwu Liu School of Materials Science and Engineering South China University of TechnologyGuangzhou 510640China Guangdong Research Institute of Rare Metals Guangzhou 510651China

The micro structure, especially the Nd-rich phase and the grain boundary, in sintered NdFeB magnets plays an important role in magnetic reversal and coercivity mechanism. To better understand the effects of the microstructure on the coercivity, we investigated the microstructure and properties improvements of a commercial sintered NdFeB magnet after optimized additional heat treatment. The coercivity is enhanced from 1399 to 1560 kA/m. This enhancement has been explained in terms of the evolution of the grain boundary structure, and the formation of continuous thin layers of Nd-rich phase is important for high coercivity. The micromagnetic simulation together with the numerical analysis based on the nucleation model suggest that the reversed magnetic domains nucleate mainly at the interface of multijunctions of Nd_2 Fe_（14）B grains with high stray fields during the demagnetization process. Both improved anisotropy fields at grain boundaries and reduced stray fields at multi-junction Nd-rich phases contribute to the coercivity enhancement. This work has importance in understanding the crucial micro structure parameters and enhancing the obtainable properties for sintered NdFeB magnets.

关键词： Sintered NdFeB magnets Microstructure Coercivity Micromagnetic simulation Heat treatment Rare earths

^(57)Fe Mössbauer spectrometry: A powerful technique to analyze the magnetic and phase characteristics in RE–Fe–B permanent magnets

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Chinese Physics B 2021年第1期30卷 73-86页

作者： lizhong zhao Xuefeng Zhang Mi Yan Zhongwu Liu Jean-Marc Greneche Institute of Advanced Magnetic Materials College of Materials&Environmental EngineeringHangzhou Dianzi UniversityHangzhou 310018China State Key Laboratory of Silicon Materials School of Materials Science and EngineeringKey Laboratory of Novel Materials for Information Technology of Zhejiang ProvinceZhejiang UniversityHangzhou 310027China School of Materials Science and Engineering South China University of TechnologyGuangzhou 510640China Institut des Mol´ecules et Mat´eriaux du Mans CNRS UMR-6283 Le Mans Universit´eLe Mans F-72085France

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.

关键词： ^(57)Fe Mössbauer spectrometry Nd–Fe–B-based permanent magnets (Ce,Nd)_(2)Fe_(14)B phase grain boundary phase

Simultaneous enhancement of coercivity and electric resistivity of Nd-Fe-B magnets by Pr-Tb-Al-Cu synergistic grain boundary diffusion toward high-temperature motor rotors

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Journal of Materials Science & Technology 2023年第23期154卷 54-64页

作者： Jiayi He Jinwen Hu Bang Zhou Haoyang Jia Xiaolian Liu Zhenhua Zhang Lin Wen lizhong zhao Hongya Yu Xichun Zhong Xuefeng Zhang Zhongwu Liu School of Materials Science and Engineering South China University of Technology Guangzhou 510640 China Institute of Advanced Magnetic Materials Hangzhou Dianzi University Hangzhou 310012 China

To high-power permanent magnetic motors,it is critical for Nd-Fe-B magnets to maintain the desirable coercivity at high-temperature operating *** address this,two approaches have been proven effective:(1)enhancing the room temperature coercivity;(2)reducing the eddy current ***,these two items are difficult to be simultaneously ***,the grain boundary diffusion(GBD)of the Pr-Tb-Al-Cu-based source is applied to enhance the coercivity and electric resistivity at room temperature from 1101 kA m-1 and 2.13×10–6Ωm to 1917 kA m-1 and 2.60×10–6Ωm,and those at 120°C from 384 kA m-1 and 4.31×10–6Ωm to 783 kA m-1 and 4.86×10–6Ωm,*** optimization is ascribed to the improved formation depth of Tb-rich 2:14:1 shells with large magnetocrystalline anisotropy and the increased intergranular Pr-based oxides with high electric resistivity,induced by the coordination effects of Tb and Pr,as proven by the atomic-scale observations and the first principles *** thus results in the simultaneously improved output power and energy efficiency of the motor because of the combination of magnetic thermal stability enhancement and eddy current loss reduction,as theoretically confirmed by electromagnetic simulation.

关键词： Nd-Fe-B Grain boundary diffusion Coercivity Electrical resistivity Eddy current loss

Grain boundary construction and properties enhancement for hot deformed(Ce,La,Y)-Fe-B magnet by a two-step diffusion process

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Journal of Materials Science & Technology 2023年第34期165卷 253-261页

作者： Xuefeng Liao Weiwei Zeng lizhong zhao Qing Zhou Jiayi He Wei Li Xiangyi Liu Hongya Yu Xiaolian Liu Haoyang Jia Jean-Marc Greneche Xuefeng Zhang Zhongwu Liu School of Materials Science and Engineering South China University of TechnologyGuangzhou 510640China Institute of Advanced Magnetic Materials College of Materials&Environmental EngineeringHangzhou Dianzi UniversityHangzhou 310018China Guangdong Provincial Key Laboratory of Rare Earth Development and Application Institute of Resources Utilization and Rare Earth DevelopmentGuangdong Academy of SciencesGuangzhou 510640China School of Materials Science and Engineering Nanchang Hangkong UniversityNanchang 330063China Institut des Molécules et Matériaux du Mans IMMM CNRS UMR-6283 Le Mans UniversitéAvenue MessiaenLe Mans F-72085Cedex 9France

The rare earth-iron-boron magnets based on high abundance rare earths(REs)show potential for costeffective permanent magnets but their hard magnetic properties have to be greatly *** grain boundary diffusion process(GBDP)is known as an effective way to improve the coercivity of Nd-Fe-B magnets,however,the conventional diffusion method faces a challenge for Ce-based magnets since there is no enough continuous GB layer as the diffusion ***,a two-step(Nd-Cu doping followed by Nd-Cu diffusion)GBDP was introduced for hot deformed(Ce,La,Y)-Fe-B magnet,and the excellent magnetic properties ofμ0Hc=0.63 T,μ0Mr=0.68 T,and(BH)max=72.4 kJ/m^(3)were *** Nd-Cu doping helps the formation of RE-rich GB layer,and then it acts as the diffusion channel for increasing the ef-ficiency of the subsequent Nd-Cu diffusion and results in the increased volume fraction of continuously distributed GB phase,whose paramagnetism was verified by 57Fe Mössbauer *** paramagnetic GB phases help to form the discontinuous domain walls,as observed by Lorentz transmission electron microscopy,and break the magnetic exchange coupling of RE2Fe14B *** thus contributes to the coercivity enhancement of the hot deformed magnet with two-step diffusion,which is further proved by micromagnetic *** study proposes a potential technique to prepare anisotropic hot deformed(Ce,La,Y)-Fe-B magnet with high cost-performance.

关键词： High abundance rare earth Hot deformed RE-Fe-B magnets Grain boundary diffusion process Magnetic properties Grain boundary phase