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Journal of Rare Earths 2024年第7期42卷 1282-1288页

作者： Yikuan Hu Jiajie Li Shengyu Sun Shuwei Zhong Munan Yang Xiaoqiang Yu Sajjad Ur Rehman Xi Yu Jiangxi Key Laboratory for Rare Earth Magnetic Materials and Devices College of Rare EarthsJiangxi University of Science and Technology National Rare Earth Functional Materials Innovation Center Ganzhou Fortune Electronic Ltd.

It is still a challenge to simultaneously enhance coercivity(Hcj) and remanence（Jr） of hot-deformed NdFe-B magnet due to the coercivity-remanence trade-off dilemma.Here,we achieved this balance between Hcjand Jrby flake Cu powder assisted DyF3interflake addition.The Hcjincreases from 1218 to1496 kA/m and Jrincreases from 1.32 to 1.34 T compared with the original magnet.Results show that the width of coarse grain layers reduces because of the introduction of flake Cu,which increases the contact areas of the adjacent grains at ribbon interfaces and suppresses the excessive growth of grains.The stronger degree of texture and higher density compared with the original magnet should take the responsibility for the increase of Jr.Additionally,the aggregation regions of rare earth rich（RE-rich） phase reduce and the betterment of the microstructure is another reason for the enhancement of Jrin the flake Cu aided DyF3hot-deformed magnet.This strategy of using flake powder additives provides a promising method for optimizing microstructure and enhancing magnetic properties of hot-deformed Nd-Fe-B magnets.

关键词： Flake powder Hot-deformed magnet Interflake addition Nd-Fe-B Rare earths remanence

Enhanced hydrogen evolution reaction in FePt film with remanence due to decrease in domain walls

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Rare Metals 2024年第3期43卷 1108-1115页

作者： Hong Hong Dong-Xue Liu Jun Li Jun-Ming Li Li-Qian Wu Bo Yang Qing-Qi Cao Dun-Hui Wang National Laboratory of Solid State Microstructures Collaborative Innovation Center of Advanced MicrostructuresJiangsu Provincial Key Laboratory for NanotechnologySchool of PhysicsNanjing UniversityNanjing210093China Hangzhou Dianzi University Hangzhou310018China Key Laboratory for Anisotropy and Texture of Materials(Ministry of Education) School of Material Science and EngineeringNortheastern UniversityShenyang110819China

As an effective strategy to improve the properties of electrocatalysts,magnetic field-assisted electrocatalytic water splitting has attracted increasing attention recently.However,the corresponding enhancements mostly depend on the exertion of an external magnetic field during electrochemical reactions,which results in a high cost of industrial production,and makes the magnetic field manipulation of electrocatalysis become a challenging task.In this work,instead of the external magnetic field,a bias magnetic field is self-supplied by the remanence state of a ferromagnetic electrocatalyst of FePt.Owing to the assistance of this bias magnetic field,the FePt film in the remanence state shows the overpotential of 229 mV during hydrogen evolution reaction,which is much lower than that in its demagnetization state(283 mV).Our findings demonstrate that the remanence in ferromagnetic electrocatalysts can improve the catalytic performance,which is attributed to the decrease in domain walls.

关键词： remanence Magnetic domains Electrocatalysis Hydrogen evolution reaction(HER)

Lanthanide single-molecule magnets with high anisotropy barrier:where to from here?

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National Science Review 2022年第12期9卷 67-69页

作者： Zhenhua Zhu Jinkui Tang State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry Chinese Academy of Sciences University of Chinese Academy of Sciences University of Science and Technology of China

Lanthanide complexes with magnetic hysteresis known as lanthanide singlemolecule magnets (Ln-SMMs) are promising candidates for high-density information storage and quantum technologies.Due to the predominantly electrostatic nature of 4f-ligand interactions,the coordination geometry of lanthanide complexes is contingent upon the steric constraints.

关键词： TEMPERATURE RELAXATION remanence

Unraveling the correlation between the remanence ratio and the dipolar field in magnetic nanoparticles by tuning concentration, moment, and anisotropy

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Nano Research 2016年第9期9卷 2772-2781页

作者： Bingqian Geng Zongling Ding Yongqing Ma Anhui Key Laboratory of Information Materials and Devices School of Physics and Materials ScienceAnhui UniversityHefei 230601China

Well-dispersed, uniform cobalt ferrite (CoFe2O4) nanoparticles (NPs) with diameters of 9, 11, 14, and 30 nm were synthesized by thermal decomposition of a metal–organic salt. Multiple variables, including the interparticle distance, moment, and anisotropy, were altered by dilution in a silica matrix and reduction in hydrogen to reveal the intrinsic correlation between the ratio of remanence to saturation magnetization (M r/M s) and interparticle dipolar interactions, the strength of which was estimated by the maximum dipolar field H dip. To date, this correlation has not been systematically investigated experimentally. To prevent the particles from agglomerating, the reduction was performed after dilution. The results revealed that the correlation between M r/M s and H dip roughly followed M r/M s ∝ 1/lgH dip independent of the size, distance, moment, and anisotropy of the magnetic nanoparticles. In particular, the correlation was closer for the nanoparticle systems that had higher concentrations or moments, that is, stronger dipolar interactions. For the single-phase CoFe2O4 nanoparticles, deviation from M r/M s ∝ 1/lgH dip can be attributed to the effects of surface spin, and for the slightly reduced nanoparticles, this deviation can be attributed to the pinning effect of CoFe2O4 on CoFe2.

关键词： magnetic nanoparticle cobalt ferrite dipolar interaction remanence ratio

remanence acquisition and its alteration on sediments

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Chinese Science Bulletin 1998年第17期43卷 1421-1434页

作者： ErwinAppel Nanjing Institute of Geography & Limnology Chinese Academy of Sciences Nanjing China Institut für Geologie und Palaeotonologie Universitat Tübingen Tübingen Germany

Previous palaeomagnetic work shows that the mechanism of remanence acquisition on sediments is very complicated. Different magnetizing processes under different conditions may produce some anomalous magnetic signals which have nothing to do with the changes of the geomagnetic field and are difficult to explain.;The depositional remanent magnetization (DRM) may produce an inclination error and a bedding error, while postdepositional remanent magnetization (PDRM) may result in a time delay between the magnetic and sedimentary ages. When there are some different magnetic phases with different lock-in depths in the sediments, it is difficult to judge the depth of the reversal or excursion, or even the artificial magnetic signal may be produced. Even if there is only one magnetic phase in the sediment, the recorded magnetic signals may also be different if the lock-in depth is changed comparative to the lasting period of one reversal or excursion. Demagnetization may also change the primary magnetic records and the changes of water content may result in the displacement of magnetic boundary. The so-called "unstable core", representing subtle changes in mineralogy into and out of a self-reversal region or a viscous magnetization region, gives a complicated palaeomagnetic record with many apparent changes in the palaeomagnetic direction. Moreover, some physical disturbances, such as biodisturbance, deformation, drilling processes and drying effects, may result in the remanence alteration. Some palaeomagnetic investigations demonstrate that good magnetic signals are invariably achieved on homogenous mud or clay sediments, but the worse signals on inhomogeneous profiles, especially on sandy layers.

关键词： remanence acquisition alteration sediment.

Low remanence temperature coefficient Sm1-xErx(Co,Fe,Cu,Zr)z magnets operating up to 400℃

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Rare Metals 2020年第1期39卷 70-75页

作者： Tian-Li Zhang Bo Zhang Hui Wang Cheng-Bao Jiang Zhi-Hong Zhang Xiao-Qing Wang Wei Zhang School of Materials Science and Engineering Beihang UniversityBeijing100191China State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization Baotou Research Institute of Rare EarthsBaotou014030China

Er-doped Sm1-xErx(CobalFe0.15Cu0.08Zr0.03)7.8(x=0,0.1,0.2,0.3)magnets with a low remanence temperature coefficient were prepared by powder metallurgy method.The influence of Er content on the remanence and microstructure was investigated.X-ray diffractometer(XRD)analysis showed that the magnets with different Er contents consist of 2:17 R phase and 1:5 H phase.Scanning electron microscopy(SEM)analysis showed that the composition of the matrix is consistent with stoichiometric composition and no obvious precipitated phase appears.With the increase in doped Er amount,the temperature stability of Sm1-xErx(CobalFe0.15Cu0.08Zr0.03)7.8(x=0,0.1,0.2,0.3)is getting better.When x is up to 0.3,the magnets with a low remanence temperature coefficient are obtained and the remanence descends tardily from 0.86 to 0.80 T as the temperature rises from room temperature to 400℃.These results indicate that Er substitution for Sm in SmCobased permanent magnets together with optimal composition and proper heat treatment could achieve a desired magnetic performance combined with high thermal stability.

关键词： Permanent magnets Low remanence temperature coefficient Er doped Magnetic performance characterization

Investigation of Surface-inset Machines with Mixed Grade Magnets Considering Magnet Thickness

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CES Transactions on Electrical Machines and Systems 2022年第3期6卷 252-260页

作者： Youyuan Ni Liang Zhang Zhiwei Qiu the School of Electrical Engineering&Automation Hefei University of TechnologyHefei230009China

This paper presents a mixed grade magnet model for surface-inset machines considering the magnet thickness. In the polar coordinates, on the basis of the Laplace/quasi-Poisson equations and boundary conditions, the constructed matrix equations are solved and the air gap magnetic field in the machine is derived. Taking an 8-pole/12-slot surface-inset motor as an example, through the presented optimization process, the air gap field is optimized considering the magnet thickness, remanence and magnetization angle. In addition, the back-EMF and electromagnetic torque are analytically obtained. The optimized results show that the proposed mixed grade magnet model has larger electromagnetic torque and smaller torque ripple than the conventional one. Finally, the analytical predictions are evaluated by finite element analysis(FEA).

关键词： Mixed grade magnet Surface-inset machines Magnet thickness remanence Torque ripple

Effects of grain size distribution on remanence and coercivity of Pr2Fe14B nanocrystalline magnet

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Chinese Physics B 2005年第5期14卷 1055-1059页

作者：贺淑莉张宏伟荣传兵陈仁杰沈保根 StateKeyLaboratoryofMagnetism InstituteofPhysicsandCentreforCondensedMatterPhysicsChineseAcademyofSciencesBeijing100080China StateKeyLaboratoryofMagnetism InstituteofPhysicsandCentreforCondensedMatterPhysicsChineseAcademyofSciencesBeijing100080China//DepartmentofPhysicsCapitalNormalUniversityBeijing100037China

The demagnetization curves of Pr2Fe14B nanocrystalline magnets are calculated using micromagnetic finiteelement method. Samples with three different distributions of grain size are simulated. We find that the remanence enhancement does not depend on grain size distribution but on the mean diameter of grains, and the influence of grain size distribution on coercivity is affected by the strength of intergrain exchange coupling.

关键词： nanocrystalline magnets coercivity remanence

Phase Formation and Magnetic Properties of Nanocomposite Nd-Fe-B Adjusted by Small Amount of Dy and Co

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Journal of Rare Earths 2004年第Z2期22卷 89-94页

作者： T S Jang T W Lim H S Aum D H Lee M B Kim Division of Materials and Chemical Engineering Sun Moon UniversityKorea Division of Materials and Chemical EngineeringSun Moon UniversityKorea Division of Mechanical EngineeringSun Moon University 100 Kalsan LiTangjung MyonAsan CityChoongnam 336-708Korea Division of Materials and Chemical EngineeringSun Moon UniversityKorea Division of Materials and Chemical EngineeringSun Moon UniversityKorea

In order to improve and stabilize the magnetic properties of nanocomposite Nd2Fe14B/α-Fe magnetic alloys by a compositional adjustment, small amount of Dy and/or Co was added to Nd9Fe84B7 alloys. DTA analysis on the amorphous of the alloys took place as the soft magnetic phases were crystallized, and then the hard magnetic Nd2Fe14B was precipitated from them. While α-Fe and a metastable 1:7 (TbCu7-type) phase were formed simultaneously in Dy and Co-free alloys, they were crystallized separately at different temperatures after Dy or Co was added. This phase separation occurred more clearly in the Dy-treated alloys and the other soft magnetic phase Fe3B was also stabilized by Dy and/or Co. The 1: 7 phase that was stabilized by Dy and/or Co was not eliminated at 700 ℃, decreasing magnetic properties of the alloys. It was eventually disappeared above 725 ℃, but Fe3B was not eliminated even at 750 ℃ when Dy was added more than 0.5 at% or Co was added more than 2.0 at%. Amount of Nd2Fe14B in the alloys tended to increase as Dy addition increased,whereas Co addition did not lead to any appreciable change in the ratio of α-Fe and Nd2Fe14B. Moreover, Dy addition apparently increased coercivity of an alloy while Co addition had a beneficial effect on remanence. The grains in the Dytreated alloys were usually finer than those in the Co-treated alloys. The grain size of both α-Fe and Nd2Fe14B in the alloys exhibiting mr ≥ 0.72 was in the range of 20 ～ 40 nm or even larger 50 nm, which is larger than the theoretical optimum size ( ～ 10 nm). Typical magnetic properties obtained from a Nd7.5Dy1.5Fe82.5Co1.5B7 alloy annealed for 12 min at 725 ℃were iHc=4.85 kOe, Br= 11.32 kG, (BH)max = 15.73 MGOe, and mr=0.73.

关键词： nanocomposite Nd-Fe-B magnetic properties remanence coercivity

Computer Simulation of Effect of Intergrain Exchange Interaction on Magnetic Properties of Nanocomposite Magnets

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Journal of Rare Earths 2004年第1期22卷 146-151页

作者： Fukunaga H Mukaino H Department of Electrical Engineering & Electronics Graduate School of Science & Technology Nagasaki University Nagasaki 852-8521 Japan Nagasaki University Nagasaki 852-8521 Japan

Effects of the intergrain exchange interaction on magnetic properties of nanocomposite magnets were investigated by using the computer simulation based on the micromagnetic theory. The simulation was carried out under the assumptions that the strength of the intergrain exchange interaction is weaker than that of the intragrain exchange interaction, that inhomogeneous nanostructures result in the distribution of the strength of the intergrain exchange interaction, and that there exists nonmagnetic intergranular phase (NMIP) between grain boundaries. The distribution of the strength of the intergrain exchange interaction was simulated by the lognormal distribution with the standard deviation of σ.The calculations for Nd 2Fe 14B/α-Fe nanocomposite magnets reveal that a suitably weak intergrain exchange interaction and small grain size enable us to improve magnetic properties. It is also found that a Nd 2Fe 14B/α-Fe nanocomposite magnet has a potential of a (BH) max value exceeding 300 kJ·m -3. On the other hand, the calculations for Nd 2Fe 14B/Fe 3B nanocomposite magnets reveal that the distribution of the strength of the intergrain exchange interaction deteriorates magnetic properties significantly. Particularly, this tendency is remarkable, when the grain size L is larger than its optimum value, 11 nm. The existence of nonmagnetic boundary layers accelerats this tendency. At σ=0.2, the calculated demagnetization curve for the model magnet composed of Nd 2Fe 14B(36%)/Fe 3B(54%)/NMIP(10%) (Valume fraction) grains (L=15 nm) agrees with that obtained experimentally for a Nd 2Fe 14B/Fe 3B nanocomposite magnet. These results suggest importance of refinement of grain size, suppression of a nonmagnetic intergranular phase, and preparation of homogeneous nanostructure for superior magnetic properties.

关键词： metal materials nanocomposite magnet exchange interaction nanostructure remanence intergranular phase