A NEUTRON POWDER DIFFRACTION STUDY OF THE STRUCTURE IN Nd2Fe17Nx(x = 2.5, 3.0, 5.5)

The crystallographic and magnetic structures of Nd₂Fe₁₇N_x(x = 2.5, 3.0, 5.5) at room temperature were refined by Rietveld analysis of neutron powder diffraction data. We found that Nd₂Fe₁₇N_x has a Th₂Zn₁₇ type structure (S.G. R3m) and the nitrogen atoms occupy both 9e and 18g sites simultaneously and at different rates.     

Y2(Fe1-xSix)14B的中子衍射研究

Nd₂Fe₁₄B是一种磁能积很高的优良的永磁材料,但在实用上稍嫌它的居里温度低了一点。为了提高它的居里温度,人们曾用某些元素替代其中的一些铁作了尝试。文献[9]及我们最近的实验表明:用硅代替部分铁之后,材料的居里点都获得了提高。本文用中子衍射法研究了Si在Y₂Fe₁₄B中的占位情况,以了解Si对磁性能产生的影响。中子衍射的结果表明:Si择优地占据c,j₁及k₂晶位。最后,用磁交换作用对结果进行了讨论。 关键词：     

Nd2(Fe,Si)17合金的结构与磁性

本文对Nd-Fe-Si三元系富铁区域相的结构和磁性进行了研究。结果表明,Nd-Fe-Si三元系富铁区域(Fe>40at％),除出现NdFe₂Si₂三元金属间化合物外(Si>20at％),同时只出现Nd₂(Fe,Si)₁₇赝二元金属间化合物,其中Si取代9d位的Fe原子,而不能形成类似于Nd₂Fe₁₄B的三元金属间化合物,Si取代Nd₂Fe₁₇中的9d位Fe原子后,使晶胞体积缩小;使饱和磁化强度减小;同时使Fe次晶格的铁磁相互作用增强,导致居里温度增高;还使得Fe次晶格的易面各向异性减弱,造成室温下各向异性场减小。 关键词：     

Si对Nd2Fe14B四方相结构和磁性的影响

本文对Si加入Nd₂Fe₁₄B四方相后所形成的合金相的结构和磁性进行了研究。结果表明,Si加入Nd₂Fe₁₄B四方相后并不破坏它的结构(Si的含量可达B的两倍),而形成Nd₂(Fe,Si)₁₄B赝三元金属间化合物。随着Si含量的增加,晶格常数和饱和磁化强度随之减小,但居里温度则随之增加。Si的加入,并不改变Nd₂Fe₁₄B的室温各向 关键词：     

永磁性大块金属玻璃Nd60Al10Fe20Co10低 温磁性的研究

研究了Nd₆₀Al₁₀Fe₂₀Co₁₀ 大块金属玻璃 磁性随温度的变化关系，结果表明Nd₆₀Al₁₀Fe₂₀Co₁₀ 在室温下 表现为永磁性，随着温 度的降低，矫顽力和磁滞回线形状都有很大的变化.交流磁化率在18 K左右出现尖峰而且峰 值温度随频率变化，表明该大块非晶体系中存在自旋玻璃态. 关键词： 大块金属玻璃 低温磁化率 自旋玻璃     

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.     

热处理对非晶态合金Nd4Fe96-xBx磁性的影响

本文研究了用单辊急冷方法制备的非晶态合金Nd₄Fe_96-xB_x的晶化,以及热处理对其硬磁性和相组成的影响,发现非晶态合金Nd₄Fe_96-xB_x的晶化温度比相同B含量的非晶态合金Fe_100-xB_x高120—190K,X射线衍射和热磁测量表明,15≤x≤25的样品晶化相是由Nd₂Fe₁₄B(T 关键词：     

MAGNETIC PROPERTIES AND CRYSTALLIZATION OF THE RAPIDLY QUENCHED (Fe1-xNdx) 81.5B18.5 ALLOYS

Magnetic properties and crystallization behaviors of amorphous (Fe_1-xNd_x) _81.5B_18.5 alloys were studied. The crystallization temperature is found to rise at first and then drop monotonically with x, having a maximum value of 976K at x=0.11 (9at% Nd). The (Fe_1-xNd_x) _81.5B_18.5 alloys prepared at a quenching rate of v_s = 6.6m /s are amorphous, and exhibit good glass formability. Both the coercive field H_c and energy product (BH)_max depend strongly on Nd concentration. Amorphous (Fe_1-xNd_x) _81.5B_18.5 alloys with higher Nd concentration have a high coercive field at low temperature, due to the large random uniaxial anisotropy of Nd. The room-temperature H_c and (BH)_max obtained on optimal annealing con-ditions show two maxima as a function of Nd concentration x. The highest room-temperature coercive field H_c =22 kOe within the Nd concentrations around x=0.368 and the maximum energy product(RH)_max= 13.3 MG·Oe at x =0.055 are observed. The hard magnetic properties of these crystallized samples are related to the presence of the bard magnetic Nd₂Fe₁₄B phase.     

Temperature dependence of the coercivity in Nd60Fe30−xCoxAl10, x=0 or 10, and Pr58Fe24Al18 bulk amorphous ferromagnets

Bulk amorphous ferromagnet alloys of composition Nd₆₀Fe₃₀Al₁₀, Nd₆₀Fe₂₀Co₁₀Al₁₀ and Pr₅₈Fe₂₄Al₁₈ have been prepared by argon arc melting and quenching into a copper mould. General insight into the magnetic behaviour of the alloys was gained from measurement of the major hysteresis loop at room temperature, and from zero-field cooled and field-cooled magnetisation measurements in the range 10-400 K. Measurements of the coercivity were made from 10 to 400 K, and for all alloys, the coercivity is seen to increase steeply with decreasing temperature to a peak at a temperature in the range 25-50 K, before decreasing. For all alloys, the temperature dependence of the coercivity between 50 and 400 K is well explained by the strong pinning model of domain walls of Gaunt [Philos. Mag. B 48 (1983) 261]. Quantities deduced from the Gaunt model, along with other relevant magnetic parameters, are used to estimate values for the exchange and anisotropy constants.     

Tetragonal rare earth (R) Iron borides,R1+εFe4B4 (ε≅0.1), with incommensurate rare earth and iron substructures

Crystallographic and magnetic properties of a new structural series of ternary borides with composition R_1+εFe₄B₄ (R = Ce, Pr, Nd, Sm, Gd, Tb, 0.11(Pr) ≤ε≤ 0.15(Tb) are reported. The compounds are built of incommensurate substructures of rare earth atoms (linear strings ?? c?), iron atoms (chains of edge sharing tetrahedra ?? c?),and boron atom pairs. A single crystal X-ray diffraction study of one representative (Sm_1.13Fe₄B₄) based on a commensurate structure model (composition : Sm₁₇(Fe₄B₄)₁₅, a = 7.07 Å, c ≡ 17c_Sm ≡ 15c_Fe= 58.69 Å, space group P4₂/n) revealed a periodic twist modulation of the Fe tetrahedra chains around c?. Magnetic susceptibility measurements on single crystals of another representative (Nd_1.11Fe₄B₄) revealed ferromagnetic ordering at T_c = 13 K. Above this temperature the magnetic properties are dominated by ferromagnetic inclusions (Fe₂B, Nd₂Fe₁₄B).     

A Mössbauer effect study of the interstitial hydrides and nitride of Nd2Fe17

The Mössbauer effect spectra of Nd₂Fe₁₇H₃, Nd₂Fe₁₇H₅, and Nd₂Fe₁₇N₃ have been measured at several temperatures between 85 and 295 K and fitted with a model which is similar to that used for the analysis of the Mössbauer effect spectra of Nd₂Fe₁₇ and Nd₂Fe₁₇N_2.6. The weighted average isomer shift increases in going from Nd₂Fe₁₇ to its hydrides and nitride, an increase which results mainly from the lattice expansion. The changes in the individual isomer shifts upon hydrogenation may be understood in terms of the expansion of the Wigner-Seitz cell volume and the presence of hydrogen or nitrogen near neighbors at a specific site. The 295 K weighted average hyperfine field increases from 157 kOe in Nd₂Fe₁₇ to 243 kOe in Nd₂Fe₁₇H₃, 280 kOe in Nd₂Fe₁₇H₅, and 318 kOe in Nd₂Fe₁₇N₃, a sequence determined by the Curie temperatures. In contrast, the weighted average hyperfine field at 85 K and the saturation magnetization at 5 K for Nd₂Fe₁₇H₃ are lower than those of Nd₂Fe₁₇, presumably because of thec-axis lattice contraction which occurs upon hydrogenation of this compound. The main difference between the effect of hydrogenation and nitrogenation resides in the substantial increase observed for the 9d and 18h hyperfine fields upon nitrogenation.     

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.     

R13Fe74Si13三元合金的结构与磁性

本文对R₁₃Fe₇₄Si₁₃(R=Ce,Pr,Nd,Gd,Tb,Dy,Ho,Er,Y)三元合金的结构和磁性进行了研究。结果表明,R₁₃Fe₇₄Si₁₃的主相为R₂(Fe_0.85Si_0.1517赝二元金属间化合物,而不出现类似于R₂Fe₁₄B的三元 关键词：     

Nano-sized disorders in hard magnetic grains and their influence on magnetization reversal at artificial Nd/Nd2Fe14B interfaces

We have investigated the effect of lattice disorders near the surface of hard magnetic Nd₂Fe₁₄B grains on coercivity using artificial interfaces created by sputter depositing Nd on polished surface of Nd-Fe-B sintered magnets. The interfacial structure was manipulated by annealing the coated samples at 550 °C in vacuum with and without Ta cap. Nano-beam electron diffraction revealed a few nm thick disordered layer within the Nd₂Fe₁₄B phase at the Nd/Nd₂Fe₁₄B interface of a low coercivity sample, while a high coercivity sample showed a well-defined crystal structure of Nd₂Fe₁₄B near the NdO_x/Nd₂Fe₁₄B interface.     

Study of the field dependence of the magnetocaloric effect in Nd1.25Fe11Ti: A multiphase magnetic system

The field dependence of magnetic entropy change ΔS_M(T,H) has been studied in the crystalline sample Nd_1.25Fe₁₁Ti, a multiphase system constituted by three phases: Fe₁₇Nd₂, Fe₇Nd and Fe₁₁TiNd. The magnetic entropy change has been calculated from the numerical derivative of magnetization curves M(T,H) with respect to temperature and subsequent integration in field. To determine the field dependence of the experimental ΔS_M, a local exponent n(T,H) can be calculated from the logarithmic derivative of the magnetic entropy change vs. field. In contrast with the results for single phase materials, where n at the Curie temperature T_C is field independent, it is shown that for a multiphase system n evolves with field both at the Curie temperature of the system and the Curie temperatures of the constituent phases. This is in agreement with numerical simulations using the Arrott-Noakes equation of state.     

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     

Magnetic properties and magnetostriction of PrxNd1-xFe1.9 (0≤x≤1.0) alloys at low temperature

The crystal structure, magnetic and magnetostrictive properties of high-pressure synthesized Pr_xNd_1-xFe_1.9 (0≤x≤1.0) alloys were studied. The alloys exhibit single cubic Laves phase with MgCu₂-type structure. The initial magnetization curve reveals that Pr_0.2Nd_0.8Fe_1.9 has a minimum magnetocrystalline anisotropy at 5 K. The magnetostriction curve at 5 K shows that Pr_0.2Nd_0.8Fe_1.9 has a very good low-field magnetostrictive property, and the magnetostriction of the Pr_xNd_1-xFe_1.9 alloy in high magnetic field is attributable mainly to Pr. The temperature dependence of the magnetostriction (λ_||) at the field of 5 kOe shows that the substitution of Nd reduces the K₁ remarkably, and the values of λ_|| of Pr_0.2Nd_0.8Fe_1.9 and Pr_0.8Nd_0.2Fe_1.9 alloys are nearly five times larger than that of PrFe_1.9 alloy below 50 K; the λ_|| of Pr_0.8Nd_0.2Fe_1.9 reaches up to 1082 ppm at 100 K, which makes it a potential candidate for application in this temperature range.     

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.     

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     

Size-dependent spin-reorientation transition in Nd2Fe14B nanoparticles

It is well known that some ferromagnetic properties like Curie temperature are size dependent. In this Letter we will report that the spin-reorientation temperature of Nd₂Fe₁₄B material is also size dependent. By using a surfactant-assisted ball milling technique, Nd₂Fe₁₄B nanoparticles with different size about 6, 20 and 300 nm were successfully obtained. Spin-reorientation transition temperature of the NdFeB nanoparticles was then determined by measuring the temperature dependence of DC and AC magnetic susceptibility. It was revealed that the spin-reorientation transition temperature (Tsr) of the nanoparticles is strongly size dependent. Tsr of the 300 nm particles is lower than that of the bulk raw material while the Tsr of the 20 nm particles is significantly lower than that for the 300 nm particles. The physics behind this size dependence is discussed.