Magnetic structure and preferential occupation of Fe in the composite compound Nd2Co6Fe

The crystal and magnetic structures of the composite compound Nd₂Co₆Fe have been investigated by high-resolution neutron powder diffraction and X-ray powder diffraction. The compound crystallizes in the hexagonal Ce₂Ni₇-type structure consisting of Nd(Co,Fe)₂ and Nd(Co,Fe)₅ structural blocks alternately stacked along the c-axis. Multi-pattern Rietveld refinement of neutron diffraction and X-ray diffraction data at room temperature reveal that substitution of Fe for Co occurs exclusively in the Nd(Co,Fe)₅ structural blocks. The preferential occupation of the Fe atoms in the structure is discussed based on the mixing enthalpy between Nd and Fe atoms and on the lattice distortions. In agreement with the reported magnetic phase diagram of the Nd₂Co_7−xFe_x compounds, magnetic structure models with the moments of all atoms in the ab plane at 300 K and along the c-axis at 450 K provide a satisfactory fitting to the experimental neutron diffraction data. The refinement results show that the atomic moments of (Co,Fe) atoms within the Nd(Co,Fe)₅ blocks decrease slightly with temperature, whereas the atomic moments of Nd in the compound and of (Co,Fe) atoms at the interface between the Nd(Co,Fe)₂ and Nd(Co,Fe)₅ blocks are reduced significantly.     

NdNi2Ge2化合物的结构和电磁输运性质

利用非自耗真空电弧熔炼法制备了NdNi₂Ge₂化合物样品,采用X射线粉末衍射技术和Rietveld全谱拟合分析方法测定了其晶体结构. 结果显示该化合物的空间群为I4/mmm,点阵参数为:a=4.120(1),c=9.835(0),Z=2,Nd原子占据2a晶位,Ni原子占据4d晶位,Ge原子占据4e晶位. NdNi₂Ge₂化合物呈现顺磁性,应用居里-外斯定律拟合计算得到居里-外斯常数为25.8,居里-外斯温度为6.24 K. 有效势磁矩为3.69μ_B,这与理论计算Nd³⁺的磁矩相符,表明磁矩主要源于Nd³⁺. 电阻率变化范围为0.3 Ω ·μm^-1-1 Ω ·μm,电阻曲线拟合显示NdNi₂Ge₂呈半金属性. 关键词： 2Ge₂')" href="#">NdNi₂Ge₂ Rietveld结构精修 电磁输运     

Enhanced alignment and magnetic properties of die-upset nano-crystal Nd2Fe14B magnets with Nb addition

It is difficult to obtain the crystallographic alignment for stoichiometric Nd₂Fe₁₄B alloys by applying the melt-spun and subsequent hot-pressing and hot-deformation techniques. However, the enhanced alignment and magnetic properties of die-upset nano-crystal Nd₂Fe₁₄B magnets have been obtained by Nb addition in the present paper. The magnetic properties studies show that Nb addition leads to the remarkable increase of remanence B_r and intrinsic coercivity H_ci, which is due to the improvement of c-axis texture and refinement of microstructure. Microstructure studies using transmission electron microscopy (TEM) and X-ray diffraction (XRD) reveal that Nb atoms are enriched at grain boundary and the NbFeB phase is observed with increasing Nb content. Since some Fe atoms in the Nd₂Fe₁₄B phase participate in the formation of NbFeB phase, the excessive Nd atoms may be enriched at grain boundary, which may improve the physical property of grain boundary and provide a mass transport pass for preferential growth of oriented Nd₂Fe₁₄B grains, thus leading to the enhanced alignment and magnetic properties.     

Electronic structure and magnetic properties of Gd3Co11B4 compound

The electronic structure of hexagonal Gd₃Co₁₁B₄ compound has been studied by X-ray photoemission spectroscopy (XPS) and ab initio self-consistent tight binding linear muffin tin orbital (TB LMTO) method. We have found a good agreement between the experimental XPS valence band spectra and theoretical LMTO calculations. Results showed that the Gd₃Co₁₁B₄ compound is ferrimagnetic with the calculated total magnetic moment M=14.29 μ_B/f.u. The values of the magnetic moments on Co atoms strongly depend on the local environment. We have also compared the electronic structure and magnetic properties of Gd₃Co₁₁B₄ compound with those of Nd₃Co₁₁B₄ compound.     

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     

电弧炉制备的Sm2Fe17-xCrx化合物的结构与磁性

通过X射线衍射、磁测量等手段对电弧炉制备的不同热处理条件的Sm₂Fe_17-xCr_x（x=1—3）化合物的结构和磁性进行了研究.结果表明1050 ℃下退火5 d的Sm₂Fe_17-xCr_x（x=1—3）化合物具有菱方相的Th₂Zn₁₇型结构,同样温度下退 关键词： 2Fe_17-xCr_x化合物')" href="#">Sm₂Fe_17-xCr_x化合物 磁体积效应 居里温度 磁晶各向异性     

Structural and magnetic properties of Sc1.1Fe3.9Al8 alloy

The crystallochemical and magnetic nature of ternary Sc_1+δFe_4−δAl₈ intermetallic with a small Sc excess δ=0.1 was investigated by scanning electron microscope, X-ray powder diffraction, neutron diffraction, Mössbauer effect and superconducting quantum interference device techniques. The sample crystallizes in a tetragonal ThMn₁₂ type structure. The excess of Sc atoms substitute Fe at the (8f) positions and have a pronounced effect on the magnetic properties. The experiments carried out in temperature range 4-320 K show that below 120 K the magnetic structure of the alloy forms a double cycloid with magnetic moments rotating according to the incommensurate in-plane wave vector, which is temperature independent up to 160 K. The value of Fe magnetic moment is close to 0.9 μ_B atom⁻¹ at 4 K. Temperature dependence of unit cell dimensions can be explained within the Debye-Grüneisen approximation.     

Site preference and thermodynamic properties of R3Ni13-xCoxB2（R=Y,Nd and Sm）

This paper investigates the structural stability of intermetallics R3Ni13-xCoxB2(R=Y,Nd and Sm) with Nd 3 Ni 13 B 2-type structure and the site preferences of the transition element Co by using a series of interatomic pair potentials.The space group remains unchanged upon substitution of Co for Ni in R3Ni13-xCoxB2 and the calculated lattice constants are found to agree with reports in literatures.The calculated cohesive energy curves show that Co atoms substitute for Ni with a strong preference for the 3g sites and the order of site preference is 3g,4h and 6i.Moreover,the total and partial phonon densities of states are first evaluated for the R 3 Ni 13 B 2 compounds with the hexagonal Nd 3 Ni 13 B 2-type structure.     

Structural, optical and magnetic properties of Nd-doped BiFeO3 thin films prepared by pulsed laser deposition

Nd-doped BiFeO₃ thin films were grown by pulsed laser deposition on quartz substrate and their structural, optical and magnetic properties have been studied. X-ray diffraction analysis revealed that Nd addition caused structural distortion even with 5% of Nd concentration, additional secondary phase appeared in all samples but its intensity was greatly reduced with Nd addition. Doping-induced variations in texture and structure modifying both magnetic and optical properties of BiFeO₃ thin films. The energy band gap decreases while the refractive index increases with addition of Nd³⁺ in BiFeO₃ for Bi³⁺. These variations in energy band gap and refractive index have been explained on the basis of density of states and increase in disorders in the system. All the samples were found to exhibit ferromagnetism at room temperature and the saturation magnetization increases with the increase in structural distortion with addition of Nd. Finally, Nd-doping modifies the physical properties of BiFeO₃ in comparison to undoped BiFeO₃ thin films.     

组合结构化合物Ho2Ni7-xFex(x=0-3.0)的晶体结构、结构转变和磁性

在金属间化合物的结构演变中,原子尺寸因素起着重要的作用.由于密堆积效应,不同原子半径比的元素往往形成不同的结构.而自由电子填充于原子构成的晶体结构的间隙中,它对化合物的结构也有影响.基于组合结构化合物Ho2Ni7-xFex,结合原子尺寸与自由电子对晶体结构的不同影响,文章探讨一种单位体积内自由电子浓度的经验方法来判断Ho2Ni7-xFex化合物中两种异构体间的转变.随着Fe含量的增加,Ho2Ni7-xFex化合物先结晶成Gd2Co7型三方结构,然后结晶成Ce2Ni7型六方结构.利用Rietveld精修技术和磁测量,获得了化合物的晶体结构参数和饱和磁化强度.化合物晶胞常数随Fe含量增加而增加,饱和磁化强度则随之减少(dMs/dx=-2).分析结果表明,单位体积内自由电子浓度更高,化合物形成三方结构,反之则形成六方结构.     

Atomistic simulation of site preference, Curie temperature, and lattice vibration of Nd2Co7 - xFex

The effects of Fe substitution for Co on the structural stability and the site preference of intermetallics Nd 2 Co 7-x Fe x with a hexagonal Ce 2 Ni 7-type structure are studied by using a series of interatomic pair potentials.In Nd 2 Co 7-x Fe x,Fe atoms are substituted for Co atoms with a strong preference for the 6h sites and the order of site preference is 6h,4e,4f,2a,and 12k.Calculated lattice parameters are found to be consistent with the reported results in the literature.The variation behaviour of the Curie temperature of Nd 2 Co 7-x Fe x is explained qualitatively by the exchange interaction model.The properties related to lattice vibration,such as phonon density of states and Debye temperature,are first evaluated for the Nd 2 Co 7-x Fe x compounds.     

Synthesis, characterization and melt processing of Y1−x(Yb0.9Nd0.1)xBa2Cu3Oz superconductors

Effects of a combined substitute of Yb and Nd on Y site on the superconducting properties of YBa₂Cu₃O_y have been studied. We synthesized Y_1−x(Yb_0.9Nd_0.1)_xBa₂Cu₃O_z compound with x = 0.2, 0.4, 0.6, 0.8 and 1.0. Here, the ratio of Yb–Nd was fixed to be 9:1 for obtaining 123 phase without secondary phases. The melt processing thermal profiles for Y_1−x(Yb_0.9Nd_0.1)_xBa₂Cu₃O_z with x = 0.2 and 0.4 and the addition of 40 mol% {Y_1−x(Yb_0.9Nd_0.1)_x}₂BaCuO₅ and 0.5 wt% Pt in air were determined on the basis of the thermal analysis results. All samples showed a low grain growth rate, particularly for high x values, which may be partially ascribed to un-optimized thermal schedules. Although almost all the samples exhibited low J_c values, the sample with x = 0.2 exhibited T_c of 88.8 K and a relatively high J_c value of 16,000 A/cm² at 77 K for H//c-axis.     

Neutron powder diffraction and magnetic studies of mesoporous Co3O4

Samples of mesoporous Co₃O₄, created by using mesoporous silicas KIT-6 and SBA-16 as hard templates to control the growth of Co₃O₄ have been investigated with SQUID magnetometry and neutron powder diffraction, to reveal the effects of high surface area on the magnetic and electronic properties. DC magnetic susceptibility measurements show lower Néel ordering temperatures and lower magnetic moments than in a “bulk” reference. A lower second transition temperature is also observed in the mesoporous samples, associated with the freezing of the surface (shell) magnetic moments. Measurements taken with increasing applied field at constant temperature show the materials to be antiferromagnetic as expected. Complementary parametric neutron powder diffraction studies show similar trends between the two mesoporous samples when looking at their Néel temperatures, and verify long range order within the samples.     

In situ high-pressure X-ray diffraction experiments and ab initio calculations of Co2P

In situ high-pressure experiments of Co2P are carried out by means of angle dispersive X-ray diffraction with diamond anvil cell technique. No phase transition is observed in the present pressure range up to 15 GPa at room temperature, even at high temperature and 15 GPa. Results of compression for Co2P are well presented by the second-order Birch-Murnaghan equation of state with V0 = 130.99(2)3 (1=0.1 nm) and K0 = 160(3) GPa. Axial compressibilities are described by compressional modulus of the axis: Ka = 123(2) GPa, Kb = 167(8) GPa and Kc = 220(7) GPa. Theoretical calculations further support the experimental results and indicate that C23-type Co2P is stable at high pressure compared with the C22-type phase.     

Y2(Fe1-x-y,Coy,Crx)17化合 物的结构及居里温度

通过x射线衍射及磁测量手段研究了Y₂(Fe_1-y-x,Co_y,C r_x)₁₇化合物的结 构及居里温度.研究结果表明Y₂(Fe_1-y-x,Co_y,Crx)₁₇化合物具有六 角相的Th₂Ni₁₇型结构.随着x的增加，Y₂(Fe 关键词： 2(Fe_1-y-x')" href="#">Y₂(Fe_1-y-x y')" href="#">Co_y x)_{1 7}化合物')" href="#">Cr_x)_{1 7}化合物 x射线衍射 居里温度     

Co和稳定元素对Nd3(Fe,Co,M)29(M=Ti,V,Cr) 化合物结构和磁性的影响

利用x射线衍射和磁测量研究了不同稳定元素Co以及Ti,V和Cr替代对Nd₃Fe_29-x-yCo_xM_y(M=Ti,V,Cr)化合物结构和磁性的影响.研究发现:每一个稳定元素都有一替代量极限,在此极限以内所有化合物均为Nd₃(Fe,Ti)₂₉型结构,A2/m空间群.不同稳定元素的溶解极限不同.Co的替代量与稳定元素有关,当以Cr作为稳定元素时,Cr的替代量随着Co含量的提高而提高 关键词： 3(Fe')" href="#">Nd₃(Fe Co 29')" href="#">M)₂₉ 结构 磁性     

Magnetic properties of NdCo2Ge2, ErCo2Ge2 and PrFe2Ge2 compounds

Magnetometric and neutron diffraction studies of polycrystalline NdCo₂GE₂, ErCo₂Ge₂ and PrFe₂Ge₂ compounds were carried out in the temperature range between 4.2 and 300 K. All samples are antiferromagnetic with Néel temperature 26.5, ～ 4.2 and 13 K, respectively. The RECo₂Ge₂ compounds have collinear antiferromagnetic order of +?+? type. For PrFe₂Ge₂ a sinusoidal magnetic structure is observed. Magnetic moment is localized on RE atoms only and is equal to that of RE³⁺ free ion value. In ErCo₂Ge₂ the magnetic moment of Er atoms is perpendicular to the c-axis, whereas for remaining compounds it is parallel to the c-axis.     

Nd5Fe18B18 (Nd1.11Fe4B4), a new nowotny-like phase. structural and magnetic properties

The crystal structure of a ternary compound, whose chemical composition is Nd₅Fe₁₈B₁₈, has been determined. Nd atoms on the one hand, Fe and B atoms on the other hand, form 2 different substructures, both of tetragonal symmetry. In a previous investigation¹ only incommensurate or very long period ordering along the $\overrightarrow{c}$ directions between the 2 substructures was proposed, with non-definite composition. The whole structure is now described in the Pccn orthorhombic space group (a=b=7.117Å ; c = 35.07Å). This compound appears then as a new Nowotny-like phase. Fe atoms are essentially non magnetic. Ferromagnetic order between Nd atoms occurs only below 14 K. 2^nd order Crystalline Electric Fiel (CEF) terms are deduced from the anisotropy of the paramagnetic susceptibility. Higher order CEF terms must also be considered.     

Influence of boron on the giant magnetocaloric effect of La(Fe0.9Si0.1)13

The influences of boron addition on the phase formation, Curie temperature and magnetic entropy change of the NaZn₁₃-type La(Fe_0.9Si_0.1)₁₃ compound have been investigated. Eight boron containing La(Fe_0.9Si_0.1)₁₃B_x samples were prepared with x=0, 0.03, 0.06, 0.1, 0.2, 0.3, 0.5 and 0.6, respectively. Experimental results show that a small amount of B addition in La(Fe_0.9Si_0.1)₁₃ forms the solid solution NaZn₁₃-type structure phase by substituting B for Si or doping B into interstitial position of the lattice, preserves its giant magnetocaloric effects due to their first-order structural/magnetic transition, as well as increase its Curie temperature T_c slightly. The maximum magnetic entropy changes in the magnetic field change of 0–1.6 T are around 20 J kg^–1 K^–1 for the samples with Boron addition less than 0.3, while improving the Curie temperatures by 2 K.     

内掺过渡金属富勒烯衍生物Ni@C20H20几何结构、成键和电磁性质的密度泛函计算研究

采用密度泛函理论中的广义梯度近似对Ni@C₂₀H₂₀的几何结构、成键和电磁性质进行密度泛函计算研究.结构优化发现位于偏离笼子中心三种位置处的Ni原子优化之后均回到笼子中心.结合能和能隙分析表明C₂₀H₂₀的中心位置是Ni原子热力学和动力学最稳定的位置.成键分析表明：Ni原子位于C₂₀H₂₀中心时,和C原子之间几乎没有相互作用,保持自己的孤立状态.电磁分析表明：原子磁矩为2关键词： 20H₂₀')" href="#">C₂₀H₂₀ 20H₂₀')" href="#">Ni@C₂₀H₂₀ 几何结构 成键 电磁性质 密度泛函理论