铌和锆对(Nd,Pr)2Fe14B/α-Fe快淬合金晶化和磁性能的影响

研究了Nb和Zr添加对快淬纳米双相(Nd,Pr)2Fe14B/α-Fe合金晶化行为和磁性能的影响. 结果表明 (Nd0.4Pr0.6)8.5Fe85.5B6合金非晶晶化时, 在α-Fe相初始晶化后, 出现了(Nd,Pr)3Fe62B14亚稳相, 最终亚稳相分解形成(Nd,Pr)2Fe14B和α-Fe两相组织; (Nd0.4Pr0.6)8.5Fe84.5Nb0.5Zr0.5B6非晶晶化时, 同时析出α-Fe相和(Nd,Pr)2Fe14B相. 这说明添加Nb和Zr可避免亚稳相的形成并细化晶粒, 最大磁能积(BH)max从复合添加前的107.5上升到143.6 kJ·m-3. 而且, Nb和Zr原子在非晶晶化过程中可以部分取代Nd和Pr的晶位, 使稀土原子可以参与形成更多的硬磁相, 进一步提高了内禀矫顽力iHc. 合金(Nd0.4Pr0.6)8.5Fe84.5Zr0.5Nb0.5 B6经690 ℃退火10 min后磁性能最优, Br=1.10 T, iHc=534.2 kA·m-1, (BH)max=143.6 kJ·m-3.     

添加镝的Nd-Fe-B纳米晶单相合金的微结构与磁性能研究

采用单辊快淬法制备了Nd12.3-xDyxFe79.7Zr0.8Nb0.8Cu0.4B6.0(x=0,0.5,1.5,2.5)合金纳米晶单相永磁薄带,研究了合金薄带晶化处理后,成分、组织结构与磁性能之间的关系.X射线衍射分析(XRD)表明,淬态合金主要由非晶相和Nd2Fe14B相组成,完全晶化后由Nd2Fe14B相和少量α-Fe组成.高分辨透射电镜(HRTEM)分析表明,经充分退火后,Nd2Fe14B晶体完整,晶粒间几乎没有边界相.随着Dy含量增加,晶粒尺寸细化,矫顽力大幅提高.x=0.5合金综合磁性能最佳,经过700℃晶化处理10min后,其磁性能为Jr=1.09 T,Hci=1048kA·m-1,(BH)max=169.5 kJ·m-3.     

热处理对非晶态合金Nd_9(FeCoZrAl)_(85)B_6磁性能的影响

采用XRD等方法研究了单辊急冷法制备的低钕含量的快淬Nd9(FeCoZrAl) 85 B6 非晶态合金在不同热处理工艺下的相组成、晶粒尺寸大小及其磁性能变化规律。热处理工艺对Nd2 Fe1 4 B相和α Fe相析出、晶粒尺寸大小和合金的磁性能具有明显影响。当热处理温度较低时 ,Nd2 Fe1 4 B相析出不充分 ,并出现不均匀长大 ,其晶粒尺寸反而较大 ;当热处理温度过高时 ,Nd2 Fe1 4 B相虽然析出充分 ,但其晶粒尺寸也明显长大 ;只有当热处理温度适中 ( 685℃ /3 0min) ,既可保证Nd2 Fe1 4 B相析出充分 ,又不至于明显长大 ,才能使Nd2 Fe1 4 B相和α Fe相、Nd2 Fe1 4 B相和Nd2 Fe1 4 B相晶粒间的磁耦合效应达到最佳 ,从而增大剩磁 ,使该合金的磁性能也达到最佳 ,制得的粘结磁体性能 :剩磁Br=65 5mT ,内禀矫顽力jHc=64 4 3kA·m- 1 ,矫顽力bHc=3 79 0kA·m- 1 ,最大磁能积 (BH) m=65 68kJ·m- 3。     

Nd10.5Pr2.5Fe80Nb1B6非晶快淬薄带等温晶化行为及矫顽力研究

研究了Nd10.5Pr2.5Fe80Nb1B6非晶快淬薄带在943,973和1003 K等温晶化与薄带组织和矫顽力的关系.结果表明,Nd10.5Pr2.5Fe80Nb1B6快淬薄带在943 K等温晶化所需晶化孕育时间为12 min,973 K时为5Inin,而1003 K时不足5lIlin.Ndl 0_5%,‰NbB6在1003K晶化25 min后所得的(Nd,Pr)2Fe14B平均晶粒尺寸为163 nm,添加Nb显著延缓了Nd10.5Pr2.5Fe80Nb1B6快淬薄带晶化后的晶粒尺寸长大.加Nb,Pr能有效提高Nd10.5Pr2.5Fe80Nb1B6的矫顽力.在973 K晶化处理19min时得到平均晶粒尺寸为96 nm的(Nd,Pr)2Fe14B单相组织,其最大矫顽力为1616 kA·m-1.     

添加铌对铜模吸铸Nd9Fe81-x-yTi4C2BxNby（x=11,13,15;y=0,4）合金铸态组织及其晶化行为的影响

采用铜模吸铸制备了厚度为0.8 mm,成分为Nd9Fe81-x-yTi4C2BxNby(x=11,13,15;y=0,4)的Nd2Fe14B/Fe3B型纳米复合永磁合金块体样品,研究了添加Nb对合金铸态组织及其晶化行为的影响,并测试了其磁性能。结果表明:在合金中添加4%(原子分数)Nb元素,不仅能抑制吸铸样品表面Nd2Fe23B3软磁性相、Nd1.1Fe4B4非磁性相和未知相的形成,导致Nd2Fe14B,Fe3B和α-Fe相的相对量增加,而且促使样品内部在非晶基体上形成了少量的Nd2Fe14B和α-Fe,Fe3B纳米晶。添加了Nb的合金吸铸样品表现出一定的硬磁性,其中Nd9Fe66Ti4C2B15Nb4吸铸样品具有最高的矫顽力(Hci=116.66 k A·m-1);添加4%(原子分数)Nb使得合金在晶化过程中由原来的异相同温一步晶化转变为两步晶化,且初始晶化温度Tx均明显降低,两个放热峰的ΔTpx均增大。     

添加铝对纳米合金Nd10.5Fe78-xCo5ZrxB6.5（x=0～5）的微观结构与磁性能的影响

研究了Zr元素对Nd10.5Fe78-xCo5ZrxB6.5(x=0，2，4，5)纳米晶双相永磁材料的磁性能与结构的影响。结果表明：适量地添加2％的Zr可以显著增强合金的内禀矫顽力，而且可以有效抑制α—Fe和Nd2Fe14B晶粒的长大，细化晶粒，改善结构。在Nd10.5Fe76Co5Zr2B6.5(x=2)合金中可以获得分布更加均匀、晶粒尺寸约为20nm的微观结构。     

铜模吸铸Nd9Fe83-xTi4C4Bx（x=1015）合金组织演化和磁性能的研究

采用铜模吸铸及随后的退火处理制备了厚度为0.8 mm,成分为Nd9Fe83-xTi4C4Bx(x=10~15)的Nd2Fe14B/Fe3B型纳米复相磁体,对其组织演变和磁性能进行了研究。结果表明:在铸态合金中,x=10的合金微观组织主要由Nd2Fe14B,Fe3B,α-Fe和TiC相构成。而x=11~15的合金中除含上述各相外,还出现了Nd2Fe23B3相、未知相和非晶相,且随着B含量的增加,它们在合金中的相对含量有不同程度的增加;退火过程中,随着合金中亚稳相和非晶相的转化,Nd2Fe14B,Fe3B和α-Fe相对含量增加,但不同B含量合金的相结构变化差异明显,导致退火后磁体具有不同的磁性能。其中,x=12的合金在680℃退火5 min后获得了最佳磁性能:Br=0.63 T,iHc=98.12 kA·m-1,(BH)max=22.79 kJ·m-3。     

淬速和热处理对纳米双相Nd2Fe14B/α-Fe磁体的性能和微结构的影响

用熔体快淬法制备了高性能纳米双相耦合Nd2Fe14B/α-Fe磁体, 研究了快淬速率和热处理工艺对其磁性能和微结构的影响. 实验结果表明, 控制快淬速率在12 m*s-1时, 可直接得到显微组织均匀、α-Fe相粒子细小且均匀分布的纳米双相耦合Nd2Fe14B/α-Fe磁体. 低温退火处理后可消除由少量非晶相带来的成分不均匀性, 其最高磁性能为iHc=432.2 kA*m-1, Jr=1.08 T, (BH)max=115 kJ*m-3. 快淬速率提高, 非晶相体积分数增加, 在高温晶化热处理时软硬磁相析出不均匀, 个别α-Fe相粒子奇异长大, 尺寸达到100 nm左右, 这不利于软硬磁相间的交换耦合作用, 有损磁性能.     

Nd60Fe20Al8Co10B2大块非晶合金晶化过程中的结构及磁性能变化

利用吸铸的方法制备了Nd60Fe20Al8Co10B2大块非晶合金。采用示差扫描量热法(DSC)，X射线衍射(XRD)，扫描电子显微镜(SEM)和振动样品磁强计(VSM)研究了Nd60Fe20Al8Co10B2大块非晶合金在晶化过程中的微观结构及磁性能的变化情况。Nd60Fe20Al8Co10B2大块非晶合金在低于723K退火时，富Nd相和富Fe相的析出对于合金的矫顽力影响不大。但是，富Fe相的长大使合金的饱和磁化强度和剩磁下降明显。合金完全晶化后，硬磁性迅速消失。     

硼对硬磁性Nd60Fe20Al10Co10大块非晶合金的磁性与晶化行为的影响

利用示差扫描量热法，X射线衍射法和振动样品磁强计研究了少量B元素对Nd60Fe20All0Col0大块非晶合金的磁性和晶化行为的影响。研究表明，用B元素部分取代Nd元素后，其内禀矫顽力有所增大，饱和磁化强度降低。晶化后，Nd60Fe20All0Col0大块非晶合金退火折出的晶体相对硬磁性能无明显影响，而Nd58Fe20All0Col0B2合金退火析出非铁磁性的Nd1.lFe4B4相，使内禀矫顽力、饱和磁化强度、居里温度降低。     

单链磁体及其研究进展

单链磁体是继单分子磁体之后分子磁学领域的又一前沿课题。对其磁特性的研究不论是在基础理论方面还是在实际应用方面都具有非常重大的意义。本文较全面地介绍了现有单链磁体的种类、结构、磁学研究方法,并对其研究方向进行了展望。     

氮氧自由基-金属配合物磁性分子材料*

氮氧自由基-金属配合物的合成和功能性研究,已成为分子磁性材料的一个热点课题。本文主要介绍了近年来氮氧自由基-金属配合物型分子基磁体、单分子磁体、单链磁体、分子自旋转换配合物等的最新研究成果,并就这一领域的发展前景做一展望。     

单分子磁体及其磁学表征*

单分子磁体是介于分子基磁体和纳米磁性材料的学科交叉点.对其不同寻常磁特性的研究不仅有助于纳米磁性离子物理学和化学的发展,而且有望最终用于高密度信息储存设备.本文就单分子磁体的研究背景和意义、单分子磁体的种类、结构及磁学表征作一概述.     

Evaluation of texture parameters in NdFeB magnets by means of X-Ray and magnetic measurements

NdFeB samples of different texture degree were prepared by uniaxial pressing in a magnetic field of different strength. Afterwards, the texture formation was investigated by means of X-ray diffraction. Usually, a fibre texture with the basal plane (001) perpendicular to the applied magnetic field is expected from the used compaction process. However, by introducing a two-parameter Gauss-function describing the texture, deviations from the rotational symmetry of the texture are found. The texture parameters are compared with those obtained by a fit of demagnetization curves. Knowing the intrinsic magnetic properties of the investigated material, demagnetization curves in the first quadrant of the J-H-plane can be calculated on the basis of the texture parameters.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Organic and Organometallic Molecular Magnetic Materials—Designer Magnets

Magnets composed of molecular species or polymers and prepared by relatively low-temperature organic synthetic methodologies are a focus of contemporary materials science research. The anticipated properties of such molecular-species-based magnetic materials, particularly in combination with other properties associated with molecules and polymers, may enable their use in future generations of electronic, magnetic, and/or photonic/photronic devices ranging from information storage and magnetic imaging to static and low-frequency magnetic shielding. A tutorial of typical magnetic behavior of molecular materials is presented. The three distinct models (intramolecular spin coupling through orthogonal orbitals in the same spatial region within a molecule/ion, intermolecular spin coupling through pairwise “configuration interaction” between spin-containing moieties, and dipole—dipole, through-space interactions) which enable the design of new molecular-based magnetic materials are discussed. To achieve the required spin couplings for bulk ferro- or ferrimagnetic behavior it is crucial to prepare materials with the necessary primary, secondary, and tertiary structures akin to proteins. Selected results from the worldwide effort aimed at preparing molecular-based magnetic materials by these mechanisms are described. Some organometallic solids comprised of linear chains of alternating metallocenium donors (D) and cyanocarbon acceptors (A) that is, …?D^?+ A^?? D^?+ A^??…?, exhibit cooperative magnetic phenomena. Bulk ferromagnetic behavior was first observed below the critical (Curie) temperature T_c of 4.8 K for [Fe^III(C₅Me₅)₂]^?+ [TCNE]^?? (Me = methyl; TCNE = tetracyanoethylene). Replacement of Fe^III with Mn^III leads to a ferromagnet with a T_c of 8.8 K in agreement with mean-field models developed for this class of materials. Replacement with Cr^III, however, leads to a ferromagnet with a T_c lowered to 3.65 K which is at variance with this model. Extension to the reaction of a vanadium(o) complex with TCNE leads to the isolation of a magnet with a T_c ≈ 400 K, which exceeds the thermal decomposition temperature of the material. This demonstrates that a magnetic material with a T_c substantially above room temperature is achievable in a molecule/organic/polymeric material. Finally, a new class of one-dimensional ferrimagnetic materials based on metalloporphins is discussed.     

Permanent magnet assembly producing a strong tilted homogeneous magnetic field: towards magic angle field spinning NMR and MRI

We introduce a cylindrical permanent magnet design that generates a homogeneous and strong magnetic field having an arbitrary inclination with respect to the axis of the cylinder. The analytical theory of 3 D magnetostatics has been applied to this problem, and a hybrid magnet structure has been designed. This structure contains two magnets producing a longitudinal and transverse component for the magnetic field, whose amplitudes and homogeneities can be fully controlled by design. A simple prototype has been constructed using inexpensive small cube magnets, and its magnetic field has been mapped using Hall and NMR probe sensors. This magnet can, in principle, be used for magic angle field spinning NMR and MRI experiments allowing for metabolic chemical shift profiling in small living animals.     

工业生产N46与N45H烧结NdFeB永磁体的结构和性能

通过优化合金成分设计和改进合金铸锭技术、合金粉末制备技术、磁场取向成型技术以及烧结技术,应用全部国产设备与国内通用的工业生产烧结NdFeB永磁的原材料,避免使用镓(Ga)等稀有贵重金属元素,实现了N46与N45H等高性能烧结NdFeB磁体的工业化生产.N46烧结NdFeB磁体的典型磁性能为Br=1.392T(13.92kGs),BH.=1004kA@m-1(12.62kOe),JH.=1085kA@m-1(13.64kOe),Hk=1008kA@m-1(1267kOe),(BH)max=366kJ@m-3(45.9MGOe).N45H烧结NdFeB磁体的典型磁性能为Bx＝1.386T(13.86kGs),BH.=1059kA@m-1(13.32kOe),JHc=1418kA@m-1(17.83kOe),Hk=1357kA@m-1(17.06kOe),(BH)max=364kJ@m-3(45.8MG0e).SEM观察和XRD分析结果表明,生产的高性能产品具有良好的取向度和晶粒细小而均匀的显微组织.     

铜、钛复合添加对结NdFeB磁体显微组织和磁性能的影响

研究了烧结NdFeB磁体晶间合添加Cu和Ti 对磁体显微组织和磁性能的影响，当钛含量小于1.2%时，Cu和Ti晶间复合添加可大幅度提高烧结NdFeB磁体的矫顽力，磁变化不大，矫顽力的提高归因于Cu和Ti在主相晶粒表面富集，细化晶粒，阻断主相晶粒之间的磁交换作用，阻碍反磁化畴的传播，当钛含量大于1.2%时，矫顽力略有下降，乘磁急剧下降，乘磁下降的原因在于出现了大量的条状纯钛相。与晶间单独合金化相比，晶间复合合金化可更有效改善NdFeB磁体显微组织与性能。     

An Exchange Mechanism for the Magnetic Behavior of Er3+ Complexes

We study the magnetic properties of the erbium based compounds, Na9[Er(W5O18)2] and [(Pc)Er{Pc{N(C4H9)2}8}]·/−, in the framework of an effective spin exchange model involving delocalized electrons occupying molecular orbitals. The calculations successfully reproduce the experimental data available in the literature for the magnetic spectrum, magnetization and molar susceptibility in dc and ac fields. Owing to their similar molecular geometry, the compounds’ magnetic behaviors are interpreted in terms of the same set of active orbitals and thus the same effective spin coupling scheme. For all three complexes, the model predicts a prompt change in the ground state from a Kramer’s doublet at zero fields to a fully polarized quartet one brought about by the action of an external magnetic field without Zeeman splitting. This alteration is attributed to the enhancement of the effect of orbital interactions over the spin exchange as the magnitude of the external magnetic field increases.