纳米晶复合Nd2Fe14B/α-Fe合金制备与磁性能的研究

采用熔体快淬及晶化处理工艺制备Nd11Fe71Co8V1.5Cr1B7.5纳米晶合金。经21m·s-1快淬及640℃ 4min晶化处理后,制成的粘结磁体的磁性能最佳,为:Br=0.64T,JHc=903.5kA·m-1,(BH)max=71kJ·m-3。添加Cr元素可提高内禀矫顽力,从而提高最大磁能积。     

Nd10.1Fe(83.7-x-y)CoxZryB6.2永磁材料结构和磁性能的研究

采用熔体快淬及晶化热处理工艺制备Nd10.1Fe(83.7-x-y)CoxZryB6.2纳米晶永磁材料. 在快淬速度为18 m·s-1时, 经710 ℃/4 min晶化处理后, Nd10.1Fe76Co5Zr2.7B6.2粘结磁体出现最佳磁性能, 分别为Br=0.67 T, JHc=754 kA·m-1, (BH)max=75.1 kJ·m-3. 粘结磁体的磁性能对于快淬速度非常敏感. 随着合金元素的添加, 出现最佳磁性能的快淬速度逐渐减少. 为了得到最佳磁性能, 除了选择合适的快淬速度外, 添加合适的合金元素变得非常重要.添加Zr元素抑制了亚稳相的析出以及细化了晶粒尺寸.比较不加Zr元素的Nd10.1Fe78.7Co5B6.2, 添加Zr元素晶化温度增加了9 ℃, 表明Zr元素也增加了快淬薄带的热稳定性.     

镨元素对(Nd,Pr)10.5(FeCoZr)83.5B6合金显微结构和磁性能的影响

研究了稀土元素Pr对快淬(Nd1-xPrx)10.5(FeCoZr)83.5B6(x=0,0.2,0.4,0.6,0.8,1.0)合金显微组织结构和粘结磁体磁性能的影响。通过部分过快淬获得由非晶和微晶共同组成的条屑,在实验优化的退火条件下晶化处理后,制备出最佳磁性能的系列粘结磁体。随Pr含量的增加,磁体的内禀矫顽力Hci单调上升,剩磁Br单调下降,(BH)m在x=0.6～0.8处达到最大值70.6kJ·m-3。Pr元素使合金非晶态的晶化转变温度和转化能降低,合金的显微组织结构变得较粗大和较不均匀,从而使快淬粘结磁体剩磁降低,但Pr2Fe14B化合物较高的磁晶各向异性场使磁体的内禀矫顽力提高。     

Formation of MgxNbyOx+y through the Mechanochemical Reaction of MgH2 and Nb2O5, and Its Effect on the Hydrogen‐Storage Behavior of MgH2

The present study aims to understand the catalysis of the MgH₂–Nb₂O₅ hydrogen storage system. To clarify the chemical interaction between MgH₂ and Nb₂O₅, the mechanochemical reaction products of a composite mixture of MgH₂+0.167 Nb₂O₅ was monitored at different time intervals (2, 5, 15, 30, and 45 min, as well as 1, 2, 5, 10, 15, 20, 25, and 30 h). The study confirms the formation of catalytically active Nb‐doped MgO nanoparticles (typically Mg_xNb_yO_x+y, with a crystallite size of 4–8 nm) by transforming reactants through an intermediate phase typified by Mg_m?xNb_2n?yO_5n?(x+y). The initially formed Mg_xNb_yO_x+y product is shown to be Nb rich, with the concentration of Mg increasing upon increasing milling time. The nanoscale end‐product Mg_xNb_yO_x+y closely resembles the crystallographic features of MgO, but with at least a 1–4 % higher unit cell volume. Unlike MgO, which is known to passivate the surfaces in MgH₂ system, the Nb‐dissolved MgO effectively mediates the Mg–H₂ sorption reaction in the system. We believe that this observation will lead to new developments in the area of catalysis for metal–gas interactions.     

添加钛和碳对Nd9.4Fe79.6B11合金晶化方式、显微结构和磁性能的影响

研究了Ti和C添加对Nd9.4Fe79.6-xTixB11-yCy(x=0,1,2,4,6;y=0.5,1.5,3)合金晶化方式、显微结构和磁性能的影响规律。结果表明,适量Ti和C添加改变了合金的晶化方式,使-αFe相和Nd2Fe14B相同时从Nd9.4Fe75.6Ti4B10.5C0.5非晶基体中析出,避免了先析出相晶粒的长大,利于获得细小均匀的显微结构。适量Ti和C添加的Nd-Fe-B-Ti-C非晶合金在退火过程中易析出细小弥散的TiC和TiB2相,可作为形核质点促进形核,且可抑制晶粒长大,最终形成细小均匀的显微结构。综合性能较佳的Nd9.4Fe75.6Ti4B10.5C0.5合金退磁曲线具有优异的方形度,最佳退火条件下合金薄带的剩磁Br为0.91 T,矫顽力iHc为976 kA.m-1,磁能积(BH)max达135 kJ.m-3。文章最后对Ti和C添加合金微结构的形成机制进行了探讨。     

Chemical Synthesis of Magnetic Nanoparticles for Permanent Magnet Applications

Permanent magnets are a class of critical materials for information storage, energy storage, and other magneto-electronic applications. Compared with conventional bulk magnets, magnetic nanoparticles (MNPs) show unique size-dependent magnetic properties, which make it possible to control and optimize their magnetic performance for specific applications. The synthesis of MNPs has been intensively explored in recent years. Among different methods developed thus far, chemical synthesis based on solution-phase reactions has attracted much attention owing to its potential to achieve the desired size, morphology, structure, and magnetic controls. This Minireview focuses on the recent chemical syntheses of strongly ferromagnetic MNPs (H_c>10 kOe) of rare-earth metals and FePt intermetallic alloys. It further discusses the potential of enhancing the magnetic performance of MNP composites by assembly of hard and soft MNPs into exchange-coupled nanocomposites. High-performance nanocomposites are key to fabricating super-strong permanent magnets for magnetic, electronic, and energy applications.     

Mechanochemical synthesis and crystal structure of acetylacetonate complexes with the triangular Mo3Q7 4+ core (Q = S or Se)

Mechanochemical reactions of inorganic polymers ¹ _∞[Mo₃Q₇Br₄] (Q = S or Se) with sodium acetylacetonate hydrate lead to excision of the Mo₃Q₇ ⁴⁺ cluster core giving rise to the cationic complexes [Mo₃Q₇(acac)₃]⁺. Extraction of the reaction mixture with acetone followed by recrystallization from a benzene-hexane mixture afforded the {[Mo₃S₇(CH₃COCHCOCH₃)₃]Br}·2C₆H₆ (1) and {[Mo₃Se₇(CH₃COCHCOCH₃)₃]Br}· · 2C₆H₆ (2) complexes. The structures of complexes 1 and 2 were studied by IR and ¹H NMR spectroscopy and X-ray diffraction. Compound 1 was characterized by electrospray mass spectrometry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1895–1898, November, 2006.     

Construction of Giant‐Spin Hamiltonians from Many‐Spin Hamiltonians by Third‐Order Perturbation Theory and Application to an Fe3Cr Single‐Molecule Magnet

A general giant‐spin Hamiltonian (GSH) describing an effective spin multiplet of an exchange‐coupled metal cluster with dominant Heisenberg interactions was derived from a many‐spin Hamiltonian (MSH) by treating anisotropic interactions at the third order of perturbation theory. Going beyond the existing second‐order perturbation treatment allows irreducible tensor operators of rank six (or corresponding Stevens operator equivalents) in the GSH to be obtained. Such terms were found to be of crucial importance for the fitting of high‐field EPR spectra of a number of single‐molecule magnets (SMMs). Also, recent magnetization measurements on trigonal and tetragonal SMMs have found the inclusion of such high‐rank axial and transverse terms to be necessary to account for experimental data in terms of giant‐spin models. While mixing of spin multiplets by local zero‐field splitting interactions was identified as the major origin of these contributions to the GSH, a direct and efficient microscopic explanation had been lacking. The third‐order approach developed in this work is used to illustrate the mapping of an MSH onto a GSH for an trigonal Fe₃Cr complex that was recently investigated by high‐field EPR spectroscopy. Comparisons between MSH and GSH consider the simulation of EPR data with both Hamiltonians, as well as locations of diabolical points (conical intersections) in magnetic‐field space. The results question the ability of present high‐field EPR techniques to determine high‐rank zero‐field splitting terms uniquely, and lead to a revision of the experimental GSH parameters of the Fe₃Cr SMM. Indeed, a bidirectional mapping between MSH and GSH effectively constrains the number of free parameters in the GSH. This notion may in the future facilitate spectral fitting for highly symmetric SMMs.     

调节层状分子基磁体[NO2BzQl][FeRuxFe(1-x)(ox)3]的合成与磁性研究

合成了组成不同的一类新的层状分子基磁体[NO2BzQl][FeRuxFe(1-x)(ox)3],并测定了它们的变温磁化率,结果显示,磁体磁性随着RuⅢ/FeⅢ比例的不同而发生变化.     

Quantification of the Magnetic Anisotropy of a Single-Molecule Magnet from the Experimental Electron Density

Reported here is an entirely new application of experimental electron density (EED) in the study of magnetic anisotropy of single-molecule magnets (SMMs). Among those SMMs based on one single transition metal, tetrahedral Co^II-complexes are prominent, and their large zero-field splitting arises exclusively from coupling between the d and d_xy orbitals. Using very low temperature single-crystal synchrotron X-ray diffraction data, an accurate electron density (ED) was obtained for a prototypical SMM, and the experimental d-orbital populations were used to quantify the d_xy-d coupling, which simultaneously provides the composition of the ground-state Kramers doublet wave function. Based on this experimentally determined wave function, an energy barrier for magnetic relaxation in the range 193–268 cm⁻¹ was calculated, and is in full accordance with the previously published value of 230 cm⁻¹ obtained from near-infrared spectroscopy. These results provide the first clear and direct link between ED and molecular magnetic properties.     

纳米BaFe12O19永磁铁氧体的制备、结构和磁性的研究

In this paper, the nanometer permanent magnetic BaFe₁₂O₁₉ powder was synthesized by a novel method of independent nucleation and crystallization steps and subsequent heat treatment,during the synthesis, Ba(NO₃)₂, Fe(NO₃)₂ and NH₄HCO₃·NH₂COONH₄ were used as starting materials. The effect of crystallization process and heat treatment conditions on the particle size, microstructure and magnetic properties of powder was studied by using XRD, TEM and vibration sample magnetometometer techniques.XRD results showed that the hematite, α-Fe₂O₃, was the main phase in the powder at heat treatment temperatures below 650℃ and its amount in the powder was decreased with increasing temperature and small amount of α-Fe₂O₃ was still remained after being heated at 900℃ for 8hrs. BaFe₁₂O₁₉ was formed about 650℃ and its amount increased in the powder as temperature raised and the higher temperature was needed to attain considerable amount of BaFe₁₂O₁₉ and ideal nanometer BaFe₁₂O₁₉ particle in the powder. The temperature between 40℃～60℃ in the crystallization process was favor to the formation of good BaFe₁₂O₁₉ crystal and to the good magnetic properties of the powder. TEM showed that the particle size in the powder increased with the enhancement of the temperature and the powder crystallized at 40℃ and heated at 800℃ for 8hrs afterwards had a very homogenous particle size distribution, and that the powder heated at 900℃ for 8hrs with the same crystalline condition as the former had a typical hexagonal shape and a chain aggregation. Specific saturation and residential magnetizations and coercive force of the powder increased mono-tonically with the increase of temperature, and reached 39.86A·m²·kg^-1, 23.96A·m²·kg^-1, 480kA·mg^-1 at 900℃, respectively.     

Divergent Coordination Chemistry: Parallel Synthesis of [2×2] Iron(II) Grid‐Complex Tauto‐Conformers

The coordination of iron(II) ions by a homoditopic ligand L with two tridentate chelates leads to the tautomerism‐driven emergence of complexity, with isomeric tetramers and trimers as the coordination products. The structures of the two dominant [Fe^II₄ L ₄]⁸⁺ complexes were determined by X‐ray diffraction, and the distinctness of the products was confirmed by ion‐mobility mass spectrometry. Moreover, these two isomers display contrasting magnetic properties (Fe^II spin crossover vs. a blocked Fe^II high‐spin state). These results demonstrate how the coordination of a metal ion to a ligand that can undergo tautomerization can increase, at a higher hierarchical level, complexity, here expressed by the formation of isomeric molecular assemblies with distinct physical properties. Such results are of importance for improving our understanding of the emergence of complexity in chemistry and biology.     

Tuning the Magnetization Dynamic Properties of Nd⋅⋅⋅Fe and Nd⋅⋅⋅Co Single‐Molecular Magnets by Introducing 3 d–4 f Magnetic Interactions

By using paramagnetic [Fe(CN)₆]^3? anions in place of diamagnetic [Co(CN)₆]^3? anions, two field‐induced mononuclear single‐molecular magnets, [Nd(18‐crown‐6)(H₂O)₄][Co(CN)₆] ? 2 H₂O ( 1 ) and [Nd(18‐crown‐6)(H₂O)₄][Fe(CN)₆] ? 2 H₂O ( 2 ), have been synthesized and characterized. Single‐crystal X‐ray diffraction analysis revealed that compounds 1 and 2 were ionic complexes. The Nd^III ions were located inside the cavities of the 18‐crown‐6 ligands and were each bound by four water molecules on either side of the crown ether. Magnetic investigations showed that these compounds were both field‐induced single‐molecular magnets. By comparing the slow relaxation behaviors of compounds 1 and 2 , we found significant differences between the direct and Raman processes for these two complexes, with a stronger direct process in compound 2 at low temperatures. Complete active space self‐consistent field (CASSCF) calculations were also performed on two [Nd(18‐crown‐6)(H₂O)₄]³⁺ fragments of compounds 1 and 2 . Ab initio calculations showed that the magnetic anisotropies of the Nd^III centers in complexes 1 and 2 were similar to each other, which indicated that the difference in relaxation behavior was not owing to the magnetic anisotropy of Nd^III. Our analysis showed that the magnetic interaction between the Nd^III ion and the low‐spin Fe^III ion in complex 2 played an important role in enhancing the direct process and suppressing the Raman process of the single‐molecular magnet.     

端视ICP-AES法测定钕铁硼永磁材料中常量及微量元素

报道了用高灵敏度的电感耦合等离子体原子发射光谱法（ＩＣＰ－ＡＥＳ）直接测定钕铁硼永磁材料中常量、少量及微量元素：Ｎｄ、Ｆｅ、Ｃｏ、Ｂ、Ｌａ、Ｃｅ、Ｐｒ、Ｄｙ、Ｇｄ、Ｓｍ、Ａｌ、Ｍｎ、Ｃａ、Ｍｇ、Ｇａ和Ｓｉ的分析方法。选择了合适的分析线，研究了基体元素Ｎｄ、Ｆｅ、Ｃｏ对被测杂质元素分析线的光谱干扰，采用基体匹配与背景扣除法进行校正。各被测元素的检出限为０．５～３０μｇ／Ｌ，回收率为９２～１１０％，相对标准偏差小于７％。本法已用于钕铁硼产品的快速检验，并获得了满意的结果。     

Liquid Nickel Salts: Synthesis,Crystal Structure Determination,and Electrochemical Synthesis of Nickel Nanoparticles

New nickel‐containing ionic liquids were synthesized, characterized and their electrochemistry was investigated. In addition, a mechanism for the electrochemical synthesis of nanoparticles from these compounds is proposed. In these so‐called liquid metal salts, the nickel(II) cation is octahedrally coordinated by six N‐alkylimidazole ligands. The different counter anions that were used are bis(trifluoromethanesulfonyl)imide (Tf₂N^?), trifluoromethanesulfonate (OTf^?) and methanesulfonate (OMs^?). Several different N‐alkylimidazoles were considered, with the alkyl sidechain ranging in length from methyl to dodecyl. The newly synthesized liquid metal salts were characterized by CHN analysis, FTIR, DSC, TGA and viscosity measurements. An odd‐even effect was observed for the melting temperatures and viscosities of the ionic liquids, with the complexes with an even number of carbon atoms in the alkyl chain of the imidazole having a higher melting temperature and a lower viscosity than the complexes with an odd number of carbons. The crystal structures of several of the nickel(II) complexes that are not liquid at room temperature were determined. The electrochemistry of the compounds with the lowest viscosities was investigated. The nickel(II) cation could be reduced but surprisingly no nickel deposits were obtained on the electrode. Instead, nickel nanoparticles were formed at 100 % selectivity, as confirmed by TEM. The magnetic properties of these nanoparticles were investigated by SQUID measurements.     

Sm2Co17型永磁合金热失效的扫描电子显微镜分析

高温度稳定型Sm2Co17永磁体的磁性能会随着使用温度的提高有所下降.为了探究高温对合金微观结构的影响,对该材料进行差热分析后得到3个明显的相变温度点:254、342和540℃.然后取同一批次的该磁体在上述温度下分别进行热处理30 min,并使用扫描电子显微镜和X射线能谱仪对处理后样品进行显微结构和成分分析.结果表明,Cu和Fe的析出和氧化是材料磁性能失效的原因,分析结果对预防该类材料失效提供了微观依据.     

Studying the Origin of the Antiferromagnetic to Spin‐Canting Transition in the β‐p‐NCC6F4CNSSN. Molecular Magnet

The crystal structure of the spin‐canted antiferromagnet β‐p‐NCC₆F₄CNSSN^. at 12 K (reported in this work) was found to adopt the same orthorhombic space group as that previously determined at 160 K. The change in the magnetic properties of these two crystal structures has been rigorously studied by applying a first‐principles bottom‐up procedure above and below the magnetic transition temperature (36 K). Calculations of the magnetic exchange pathways on the 160 K structure reveal only one significant exchange coupling (J(d1)=?33.8 cm^?1), which generates a three‐dimensional diamond‐like magnetic topology within the crystal. The computed magnetic susceptibility, χ(T), which was determined by using this magnetic topology, quantitatively reproduces the experimental features observed above 36 K. Owing to the anisotropic contraction of the crystal lattice, both the geometry of the intermolecular contacts at 12 K and the microscopic J_AB radical–radical magnetic interactions change: the J(d1) radical–radical interaction becomes even more antiferromagnetic (?43.2 cm^?1) and two additional ferromagnetic interactions appear (+7.6 and +7.3 cm^?1). Consequently, the magnetic topologies of the 12 and 160 K structures differ: the 12 K magnetic topology exhibits two ferromagnetic sublattices that are antiferromagnetically coupled. The χ(T) curve, computed below 36 K at the limit of zero magnetic field by using the 12 K magnetic topology, reproduces the shape of the residual magnetic susceptibility (having subtracted the contribution to the magnetization arising from spin canting). The evolution of these two ferromagnetic J_AB contributions explains the change in the slope of the residual magnetic susceptibility in the low‐temperature region.     

Benign‐by‐Design Solventless Mechanochemical Synthesis of Three‐, Two‐, and One‐Dimensional Hybrid Perovskites

Organic–inorganic hybrid perovskites have attracted significant attention owing to their extraordinary optoelectronic properties with applications in the fields of solar energy, lighting, photodetectors, and lasers. The rational design of these hybrid materials is a key factor in the optimization of their performance in perovskite‐based devices. Herein, a mechanochemical approach is proposed as a highly efficient, simple, and reproducible method for the preparation of four types of hybrid perovskites, which were obtained in large amounts as polycrystalline powders with high purity and excellent optoelectronics properties. Two archetypal three‐dimensional (3D) perovskites (MAPbI₃ and FAPbI₃) were synthesized, together with a bidimensional (2D) perovskite (Gua₂PbI₄) and a “double‐chain” one‐dimensional (1D) perovskite (GuaPbI₃), whose structure was elucidated by X‐ray diffraction.     

Metal Redox Processes for the Controlled Synthesis of Metal Alloy Nanoparticles

Nanocrystalline metals have received widespread interest and found various applications owing to their magnetic and catalytic properties and in energy‐related fields. A flexible approach for the growth of nanoalloys with controlled properties and well‐defined structures on the atomic scale is thus greatly desired. A new synthetic method that avoids incompatible reduction potentials and rates would be critical to grow metal nanostructures with high purities and the desired stoichiometries. A metal‐redox strategy that employs spontaneous oxidation/reduction reactions to grow nanocrystalline alloys using molecular‐scale zerovalent metal precursors is now described. The selection of suitable zerovalent metal species allows for thermodynamic control of the compositional stoichiometry during the temperature‐dependent formation of the metal alloy nanoparticles. A practical and scalable strategy for nanoalloy growth that can potentially produce key metal components of superior metallurgical quality for catalytic and magnetic systems has thus been developed.