Effect of Mn on the magnetic properties of Fe3B/Nd2Fe14B nanocomposites

The magnetic properties of Nd_4.5Fe_77−xMn_xB_18.5 (x=0, 1 and 2) nanocomposites prepared by the crystallization of amorphous precursors were investigated. Addition of Mn is found to decrease the crystallization temperature of the amorphous ribbons. The intrinsic coercivity _iH_c and maximum energy product (BH)_max increase from 2.6 kOe and 9.1 MGOe for x=0 to 3.1 kOe and 10.3 MGOe for x=1, respectively, and the remanence ratio M_r/M_s increases from 0.70 to 0.72. The effect of Mn on Curie temperature T_C and the thermal stability of M_r and _iH_c were also studied. ⁵⁷Fe Mössbauer spectra have been recorded for x=0, 1 and 2 ribbons at room temperature and site preference of the Mn atoms in Fe₃B and Nd₂Fe₁₄B phases is discussed using the Mössbauer spectroscopy.     

Nd2Fe14B的价电子结构分析和磁性计算

应用固体与分子经验电子理论计算了Nd₂Fe₁₄B的价电子结构、磁矩和居里温度,计算结果与实验值相符.计算表明:该合金的磁性与3d磁电子数成正比.从Fe(c)晶位到Fe(k₂)晶位磁矩增加,其机理源于价电子、哑对电子和3d磁电子之间的转化,有78%的哑对电子和18%的3d共价电子转化成了磁电子.居里温度和磁矩与Fe原子配位数成正比,与加权等同键数I^σ成反比,Nd原子 关键词： 2Fe₁₄B')" href="#">Nd₂Fe₁₄B 价电子结构 居里温度     

Effects of underlayer materials and substrate temperatures on the structural and magnetic properties of Nd2Fe14B films

Thin films of Nd_2Fe_{14}B were fabricated on heated glass substrates by dc magnetron sputtering. Different material underlayers (Ta, Mo, or W) were used to examine the underlayer influence on the structural and magnetic properties of the NdFeB films. Deposited on a Ta buffer layer at 420℃, the 300 nm thick NdFeB films were shown to be isotropic. But when the substrate temperature T_s was elevated to 520℃, the Nd_2Fe_{14}B crystallites of (00l) plane were epitaxially grown on Ta (110) underlayer. In contrast, Mo (110) buffer layer could not induce any preferential orientation in NdFeB film irrespective of the substrate temperature or film thickness. The W buffer layer was found to be most effective for the nucleation of Nd_2Fe_{14}B crystallites with c-axis alignment perpendicular to the film plane when T_s<490℃. But at T_s=490℃ the magnetic layer became isotropic. The maximum coercivity obtained was about 995 kA/m for the 100nm film deposited on W underlayer at 490℃. These variations were tentatively explained in terms of the lattice misfit between the underlayer and the magnetic layer, combined with the considerations of underlayer morphologies.     

Research on preparing compact bulk nanocomposite Nd2Fe14B/α-Fe magnetic materials by hot extrusion

In this paper, compact bulk nanocomposite Nd₂Fe₁₄B/α-Fe magnetic materials were prepared by hot extrusion of amorphous and nanocrystalline powders, which were prepared by high-energy ball-milling (HEBM) of the Nd₂Fe₁₄ B-type hard magnetic phase with 20 vol% of α-Fe as soft magnetic phase. The extrusion temperature has important influence on magnetic properties and microstructure of magnetic materials. The results show that the grain size of Nd₂Fe₁₄B and α-Fe phase increases steadily with increasing extrusion temperature. Furthermore, optimal extrusion temperature of 1223 K occurs, at which the highest magnetic properties and relative density can be obtained.     

纳米晶复合Pr2Fe14B/α-Fe永磁材料磁性的研究

采用熔体快淬的方法制备Pr₂Fe₁₄B/α-Fe纳米晶复合永磁材料.使用振动样品磁强计(VSM)测量样品的室温磁性能.实验合金成分为(Pr_xFe_94.3-xB_5.7)_0.99Zr₁(其中x＝8.2，8.6，9.0，9.4，9.8，10.2，10.6，11.0，11.4(原子分数，%)).系统地研究了辊速及合金成分对快淬带磁性能的影响，当Pr原子分数由8. 关键词： 纳米复合永磁材料 熔体快淬 2Fe₁₄B/α-Fe')" href="#">Pr₂Fe₁₄B/α-Fe 磁性     

相分布和晶粒尺寸对Nd2Fe14B/ɑ-Fe纳米复合永磁材料矫顽力的影响

本文采用统计平均方法研究了软、硬磁性晶粒尺寸及相分布对Nd2Fe14B/α-Fe纳米复合永磁材料矫顽力的影响。计算结果表明：对于单相纳米硬磁材料，磁体矫顽力随着硬磁性晶粒尺寸的减小而降低；对于软、硬两磁性相组成的Nd2Fe14B/a-Fe纳米复合永磁材料，两相的随机分布将导致磁体矫顽力随硬磁性晶粒尺寸的减小呈现极大值。本文的计算结果还表明当硬磁性晶粒尺寸大于软磁性晶粒的最佳尺寸时(15nm)，具有多层膜结构的Nd2Fe14B/a-Fe纳米复合永磁材料将比两相随机分布时具有更大的矫顽力。     

取向Pr2Fe14B与Nd2Fe14B多晶磁化曲线的 计算

基于单离子晶场模型,提出了计算稀土-Fe(Co)金属间化合物取向多晶样品磁化曲线的方法.用此方法计算了取向Pr₂Fe₁₄B和Nd₂Fe₁₄ B多晶的高场磁化曲线,计算中使用了拟合化合物单晶磁化曲线得到的交换场与晶场参数.计 算曲线与实验曲线相符合. 关键词： 磁化曲线 晶场 2Fe₁₄B')" href="#">R₂Fe₁₄B     

Particle analysis and properties of mechanically alloyed Nd16Fe76−xTixB8

Nanocrystalline Nd₁₆Fe_76−xTi_xB₈ hard magnetic powders were prepared by mechanical alloying and respective heat treatment at 973–1073 K /30–60 min. The nanocrystalline hard magnetic powders were investigated by the NanoSight Halo LM10^TM Nanoparticle Analysis System, AFM, SEM and Mössbauer spectrometry. The nanocrystals have average size of 40 nm and the crystals form agglomerates with an average size of about 180 nm. Halo^TM, AFM and SEM techniques are the complementary methods, which give comparable results.     

Magnetoelastic properties of Nd6Fe13Cu intermetallic compound

Magnetoelastic properties of Nd₆Fe₁₃Cu intermetallic compound are reported. To study the magnetoelastic behaviour of this compound, the thermal expansion as well as the longitudinal (λ_l) and transverse (λ_t) magnetostriction were measured by using the strain gauge method in the selected temperature range of 80-500 K under applied magnetic fields up to 1.5 T. An anomaly and invar-type effects are observed in the linear thermal expansion and α(T) curves at the Néel temperature. The linear spontaneous magnetostriction decreases sharply by approaching the Néel temperature and also shows the short-range magnetic ordering effects when antiferromagnetic-paramagnetic transition occurs. In the low field region, the absolute values of the anisotropic magnetostriction are small and then start to increase with applied magnetic field. Each isofield curve of the anisotropic magnetostriction passes through a minimum and then approaches to zero with increasing temperature. This magnetostriction compensation arises from the difference in the magnetoelastic coupling constants of the sublattices in this compound.     

冲击波诱导Nd_2Fe_(14)B磁相变的理论计算研究

根据Nd2Fe14B的冲击加载实验,计算了3.3—7.2 GPa压力范围内冲击波阵面上压力与温度的关系.基于分子场理论,引入压力等效场,改进了双亚点阵理论模型,并分析了在不同温度和压力下Nd2Fe14B的磁性转变机理.计算了压力对Nd2Fe14B磁致伸缩系数、磁化率、磁化强度以及居里温度的影响,给出了Nd2Fe14B发生铁磁–顺磁相变的压力和温度判据.计算结果表明:压力使Nd2Fe14B的居里温度逐渐向低温区转移,当压力从0 GPa增加到1.15 GPa时,居里温度从584 K降至292 K;随着压力的增加,Nd2Fe14B的磁化强度不断下降,且临界去磁压力随温度的升高呈下降趋势;在3.3—7.2 GPa压力范围内,Nd2Fe14B发生了铁磁-顺磁相变.     

Magnetic properties of Y2Fe14B and Nd2Fe14B single crystals

Y₂Fe₁₄B and Nd₂Fe₁₄B are ferromagnets in which 3d interactions are dominant. In Y₂Fe₁₄B, the

-axis of the quadraticque est de magnetization. The 3d anisotropy is an order of magnitude weaker than in YCo₅. In agreement with point-charge model, CEF potential in Nd₂Fe₁₄B favours the

-axis at 300 K. At low temperature, the magnetization reorientation observed results from competition between exchange and anisotropy.     

Elasticity in nanocrystalline Nd2Fe14B+αFe magnetic composites

The dynamic Young modulus (E) of magnetic Nd₂Fe₁₄B+αFe nanocomposites is investigated with mechanical spectroscopy techniques (vibrating reed configuration, f≈1.5 kHz <10⁻⁶). Reduced values of E are obtained (88–152 GPa) as compared with that predicted by the rule of mixtures for the composite (164 GPa). Three contributions to this reduction are briefly discussed: a large volume fraction of the specimen with grain boundary like structure; internal pores, resulting from the high cooling rate during processing (10⁶ K/min) and magneto-mechanical effects. Even when porosity is identified as the principal cause of modulus reduction, magnetic effects are also detected.     

Study of the magnetic structure for Nd2Fe14B

The method of multi-ion crystal field calculation is applied to compute the magnetic structure of Nd₂Fe₁₄B. By means of fitting calculation, a set of crystal field coefficients, cone angle θ (32°) of spin direction and the temperature of spin reorientation T_sr (130 K) are obtained, which are in good agreement with experiment. The magnetic structure of the rate earth ion Nd is determined from the calculation.     

Magnetic properties and crystal structure of Nd2Fe14B

Outstanding permanent magnet properties have recently been reported to occur in ternary compound Nd-Fe-B¹. The tetragonal crystallographic structure of this compound Nd₂Fe₁₄B is determined (space group P4₂/mnm). This structure is related to the hexagonal CaCu₅-type structure which is the fundamental basis for the crystal structure of many rare earth-transition metal compounds.     

Effects of SnO2 addition on the microstructure and magnetic properties of NiZn ferrites

The microstructure and magnetic properties of SnO₂-doped NiZn ferrites prepared by a solid-state reaction method have been investigated. Due to its low melting point (∼1127 °C), moderate SnO₂ enhanced mass transfer and sintering by forming liquid phase, which accelerated the grain growth. However, excessive SnO₂ producing much of liquid phase retarded mass transfer and sintering, leading to a decrease in grain size. The diffraction intensity of the samples doped with SnO₂ addition was stronger than that of the sample without addition. The lattice constant initially decreased up to a content of 0.10 wt% and showed an increase at higher content up to 0.50 wt%. The initial permeability (μ_i) initially increased up to a content of 0.15 wt% and showed a decrease at higher content up to 0.50 wt%; however, losses (P_L) measured at 50 kHz and 150 mT changed contrarily. Both saturation induction (B_S) and Curie temperature (T_C) decreased gradually with increasing SnO₂. Finally, the sample doped with 0.10–0.15 wt% SnO₂ showed the higher permeability and lower losses.     

晶粒易轴取向度对纳米晶永磁Pr2Fe14B磁性的影响

构造了立方和不规则形状晶粒的各向异性纳米晶单相Pr₂Fe₁₄B磁体 .利用微磁学的有限元法，模拟计算了样品的磁滞回线.计算结果表明，随着磁体晶粒易轴取向度的变差， 磁体的剩磁、矫顽力均随之下降.不同晶粒尺寸的纳米晶单相Pr₂Fe_{14B磁体，其磁 性能随取向度的变化快慢不同，原因在于磁体中的晶间交换作用 (IGEC) 的强弱不同.随着 晶粒取向度的提高，纳米晶单相磁体的矫顽力逐渐增加，这完全不同于烧结磁体. 关键词： 纳米晶磁体 矫顽力 剩磁}     

Dy在Nd2Fe14B晶格中的占位及其对Fe原子磁矩影响的第一性原理计算

基于第一性原理投影缀加波和梯度矫正局域密度近似(PAW-GGA), 研究了Nd₂Fe₁₄B和Dy₂Fe₁₄B的基态晶格属性, 进而对Dy在Nd₂Fe₁₄B晶格中的掺杂进行了研究, 并采用GGA+U的方式进行了原子磁矩计算, 并与自旋轨道耦合 (SOI) 计算结果进行了对照. 置换计算表明, Dy原子倾向于置换Nd₂Fe₁₄B晶格中4f位的稀土原子. 磁矩计算表明, 在R₂Fe₁₄B (R: 稀土元素) 晶格中, 4f位的稀土元素与Fe原子作用更强, 对磁性能的影响更大. 稀土原子与Fe的作用与距离呈正相关. 关键词： 2Fe₁₄B')" href="#">Nd₂Fe₁₄B 晶格占位 形成能 原子磁矩     

Phase composition, microstructures and magnetic properties of melt-spun Nd1.2Fe10.5Mo1.5 ribbons and their nitrides

The effect of wheel speed on the phase compositions and microstructures of melt-spun Nd_1.2Fe_10.5Mo_1.5 ribbon was investigated. It is found that the Nd(Fe,Mo)₁₂ phase can be obtained at the wheel speed of 10 m/s, and TbCu₇-type Nd(Fe,Mo)₇ phase is formed with the wheel speed higher than 10 m/s. The amorphous phase is achieved at 65 m/s. The average grain size of phases decreases linearly with increasing wheel speed. The Nd(Fe,Mo)₁₂N_1.0 nitride obtained from annealed ribbons quenched at 65 m/s shows a coercivity much higher than that from the ribbons quenched at 10 m/s, which is due to the smaller grain size in the former ribbons.     

A study of the properties and microstructure of Ni81Fe19 ultrathin films with MgO

The anisotropic magnetoresistance (AMR) of a Ta (5 nm)/MgO (3 nm)/Ni₈₁Fe₁₉ (10 nm)/MgO (2 nm)/Ta (3 nm) film with MgO-Nano Oxide Layer (NOL) increases dramatically from 1.05% to 3.24% compared with a Ta (5 nm)/Ni₈₁Fe₁₉ (10 nm)/Ta (3 nm) film without the MgO-NOL layer after annealing at 380 °C for 2 h. Although the MgO destroys the NiFe (1 1 1) texture, it enhances the specular electron scattering of the conduction electrons at the NOL interface and suppresses the interface reactions and diffusion at the Ta/NiFe and NiFe/Ta interfaces. The NiFe (1 1 1) texture was formed after the annealing, resulting in a higher AMR ratio. X-ray photoelectron spectroscope results show that Mg and Mg²⁺ were present in the MgO_x films.     

Synthesis and photoluminescence properties of Nd2O3 nanoparticles modified by sodium bis 2-ethylhexyl sulfosuccinate

This paper reports that Nd₂O₃ nanoparticles modified by AOT(sodium bis(2-ethylhexyl) sulfosuccinate) were prepared using microemulsion method in the system of water and propanol/AOT/toluene. Transmission electron microscopy shows that the Nd₂O₃ nanoparticles take the shape of sphere with 18\,nm and 31nm with different preparation. The organic sol of Nd₂O₃ nanoparticles is very stable at room temperature. X-ray diffraction results show that the product has hexagonal phase structure. Two ultraviolet emission band at 344\,nm and 361\,nm corresponding to the transition of ⁴D_3/2→4I_9/2 and 2P_3/2→⁴I₁₁₂ or ⁴D_3/2 →⁴I_13/2 were observed.