Effective magnetic fields on Fe in R1+εFe4B4 alloys

⁵⁷Fe Mössbauer spectra of magnetically ordered R_1+εFe₄B₄ alloys have been measured at low temperatures. Small (⋍ 0.8 T) hyperfine fields have been found for R = Sm and Dy. Analysis of the spectra in terms of simultaneous magnetic and quadrupolar interactions has revealed the magnetization to be parallel to the c axis for R = Sm and perpendicular to the c axis for R = Dy. These results are consistent with a 2^nd-order CEF mechanism for anisotropy. The ordering temperature of Sm_1+εFe₄B₄ was determined from Mössbauer and magnetization measurements to be T_c = 37 ± 2 K, the highest in the R_1+εFe₄B₄ series.     

Hysteresis of nanocrystalline R–Fe–B

The energetic model of ferromagnetic hysteresis calculates the magnetic state of materials by minimizing the total energy function for statistical domain behavior. The approach shows good agreement with the magnetization curves of mechanically alloyed Pr₉Fe₈₅B₆ powder, heat treated at different temperatures.     

155Gd and 161Dy Mössbauer study of R1+εFe4B4 alloys (R = Gd,Dy)

Tetragonal R_1+εFe₄B₄ alloys with R = Gd and Dy have been investigated by Mössbauer spectroscopy, using the ¹⁵⁵Gd and ¹⁶¹Dy resonances, respectively. The Gd quadrupolar interaction e²qQ = 12.65(5)mm/s is the largest observed to date in metallic compounds of Gd. For Dy this interaction is e²qQ = 74(2) mm/s, a value rather small for a Dy compound. Both results imply a strong lattice contribution to the electric field gradient. A crystal-field term A⁰₂ = -2450(50) K/a²_o is inferred. Our data are consistent with a point-charge calculation, provided charges of opposite signs are assumed for Fe and B atoms. Hyperfine parameters show some dispersion, reflecting the quasi incommensurate nature of the R and Fe+B sublattices in the R_1+εFe₄B₄ structure.     

Diffusion of Fe,Co, Nd,and Dy in R2(Fe1−xCox)14B where R=Nd or Dy

Transition metal and rare earth diffusion coefficients at 1323 K in Dy_2−yNd_y(Fe_1−xCo_x)₁₄B were determined by field emission energy dispersive spectroscopy compositional analysis of diffusion couple specimens. Various arrangements of component materials and temperatures were examined in order to understand the mechanisms affecting diffusion of the components and to predict the stability of functionally graded microstructures consisting of a dysprosium-rich (Dy_2−yNd_y(Fe_1−xCo_x)₁₄B) outer layer and a neodymium-rich (Nd₂(Fe_1−xCo_x)₁₄B) interior. Estimates of the mutual interdiffusion coefficients of Dy, Nd, Fe, and Co in this system were obtained from the preparation of arc melted and annealed polycrystalline specimens, assuming that the diffusion coefficients were independent of concentration (Grube solution). Fifteen diffusion couples were prepared and heat treated at 1323 K for various times in order to provide data for calculation of the diffusion coefficients. The results indicate that the diffusion coefficients of Fe and Co (D_Fe=3.28×10⁻¹⁰ cm²/s and D_Co=7.63×10⁻¹⁰ cm²/s) were significantly higher at 1323 K in this system than those for Dy and Nd (D_Nd=2.3×10⁻¹² cm²/s and D_Dy=2.9×10⁻¹² cm²/s).     

Observations of multi-phase microstructures in R2(Fe1−xCox)14B where R=Nd or Dy

Multi-phase microstructures were observed in the psuedo-quaternary phase field of the 2–14–1 magnet materials Nd₂Fe₁₄B, Nd₂Co₁₄B, Dy₂Fe₁₄B, and Dy₂Co₁₄B. At equilibrium, (Nd_1−yDy_y)₂(Fe_1−xCo_x)₁₄B had heretofore been widely assumed to be single phase where 1>x>0 and 1>y>0. In this study, three-phase microstructures were observed in (Nd_1−yDy_y)₂(Fe_1−xCo_x)₁₄B when x>0.3 and y>0.5. The Curie temperatures and peritectic decomposition temperatures for Nd₂(Fe_1−xCo_x)₁₄B are reported for several values of x in the range 1>x>0.     

A Mössbauer spectroscopic study of 3d magnetism of R2Fe14B

Guided by the occupancies and iron magnetic moments μ³, ⁵⁷Fe Mössbauer parameters of Y₂Fe₁₄B at 250K, and in turn for other temperatures, of the sublattices of iron were deduced. Plots of μ(T) in reduced coordinates, through the established correlation between hyperfine field Hn and μ, show that the corresponding state of different iron sites is different and all experimental points fall below Brillouin function. The relation between exchange integral deviation parameter Δ and standard deviation of Fe-Fe interatomic distances S is linear, indicating electrostatic nature of exchange interactions between spins in neighboring atoms. It is inclined to the view that fluctuations of exchange integral is responsible for low T_c of R₂Fe₁₄B.     

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Pr2 Fe14 B和Nd2 Fe14 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 .     

Structure and magnetic properties of Fe96−x Zr x B4 nanowire arrays

Fe96-xZrx B4(1相似文献   

Magnetic properties of the R1+eFe4B4 compounds (R = rare earth) from magnetization and Mössbauer measurements

The magnetic properties of rare earth-iron-boron alloys with composition R_1+eFe₄B₄ have been determined using Mössbauer and magnetization measurements. Magnetic ordering occurs at temperatures between 4.2 and 25 K for the compounds with R = Pr, Nd, Sm, Gd, Tb, Dy, Ho. The Curie temperature scales very well with the de Gennes factor for the heavy rare earth members of the series, while significant deviations are observed for the light rare earths indicating the presence of strong CEF effects. The absence of magnetic hyperfine splitting even at 4.2 K indicates that the Fe ion has a zero magnetic moment. This is confirmed by Mössbauer spectra in an applied magnetic field.     

155Gd Mössbauer investigation on (GdxNd1−x)1+εFe4B4

Tetragonal (Gd_xNd_1–x)₁₊ Fe₄B₄ alloys have been investigated for 0.2x1 by Mössbauer spectroscopy, using the 86.5 keV¹⁵⁵Gd resonance. The Gd quadrupolar interaction e²qQ=12.67(5) mm/s for x=1, nearly independent of x, is the largest observed to date in metallic compounds of Gd. A crystal field term A ₂ ⁰ =–2450±50 K/a ₀ ² is inferred. This quadrupolar interaction shows some dispersion increasing when x decreases, reflecting the quasi incommensurate nature of the (Gd,Nd) and Fe+B sublattices in the (Gd_xNd_1–x)Fe₄B₄ structure (=0.109 for x=0 and =0.139 for x=1). The hyperfine field is perpendicular to the c axis for x0, but no unique direction is obtained for x=0.     

Structural and magnetic study of bulk glassy Fe72 − x Co x B20Si4Nb4 alloys

The influence of the partial replacement of Fe by Co on the structural and magnetic properties of bulk-type glassy Fe_72???x Co _x B₂₀Si₄Nb₄ (x = 0, 5, 10, 15, 20, 25, 30, 35) alloys has been studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD) magnetic measurements and Mössbauer spectroscopy. Results show that the successive Co addition: (1) does not affect the mass density of the studied alloys, (2) affects appreciably the super cooled region, (3) modifies the magnetic properties, exhibiting soft magnetic behavior, (4) modifies the spin texture and disorder within the studied specimens.     

Die Röntgenolumineszenz der Kristalle von NaCl: Fe

Ohne Zusammenfassung

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Nacl: Fe

     

R13B1与R152a专用状态方程的研究

一、引言 表示流体P、V、T关系的专用状态方程是流体热物性研究最基础的工作,它是计算流体PVT性质及对实验数据进行内插外推及计算其导出热力性质(如焓、熵等)的工具,也是用来制作热物性图表的基础方程.一般对专用状态方程的要求应包括:1)能适用于宽广的参数范围及整个流体区域;2)不仅在计算PVT性质时精度高,而且能正确地描述其     

R2Fe14B型永磁材料中第二磁晶各向异性常数对反磁化过程的影响

针对低温下各向同性Pr2Fe14B永磁材料的最小形核场问题,用数值计算法和近似解析解研究了第二磁晶各向异性常数K2对最小形核场的影响.研究发现,尽管对于Nd2Fe14B永磁材料一级近似的解析解与数值计算结果很接近,但是对于低温下各向同性Pr2Fe14B永磁材料则至少要用二级近似下的解析解才能与数值计算结果相接近.用有关最小形核场的计算结果很好地解释了低温时各向同性Pr2Fe14B永磁材料的矫顽力与最小形核场的关系.     

水雾化制备Fe74Al4Sn2P10C2B4Si4非晶合金粉末及其磁粉芯性能研究

采用水雾化方法制备Fe7Al4Sn2P10C2B4Si4合金粉末,研究发现该合金具有强的非晶形成能力和高热稳定性,在粉末粒度小于400目时可以形成非晶态合金.采用该非晶粉末制备的磁粉芯在高频下品质因数显著高于MPP粉芯,说明该磁粉芯高频损耗较低.分析表明,非晶合金磁粉芯高频下损耗低的主要原因是电阻率较高.     

Interface mixing in Fe–B–Ag multilayers

Multilayers with Ag/Fe/B and Ag/B/Fe layer sequence were studied in order to reveal differences of top and bottom interfaces of Fe. The hyperfine field distribution depends on the layer sequence and the differences could be attributed to a different B concentration distribution at the top and bottom Fe–B interface.     

Hyperfine interactions in R x Gd1− x Fe3 intermetallics R = Tb,Y

The structural and magnetic properties of rare earth iron intermetallic compounds Tb _x Gd_1?x Fe₃ and Y _x Gd_1?x Fe₃ (x = 0. 0, 0. 1, 0. 2, 0. 4, 0. 5, 0. 6, 0. 8, 1. 0) was studied by X-ray diffraction, the ⁵⁷Fe Mössbauer effect and SQUID measurements. All investigated compounds crystallize in the rhombohedral PuNi3-type of crystal structure. The investigation of magnetic properties of R _x Gd_1?x Fe₃ proved their ferrimagnetic behavior. The Curie temperature of the investigated compounds decreases with the increase of R concentration from 721K (GdFe₃) to 655K (TbFe₃) and 533K (YFe₃). The saturation magnetic moment MS in the R _x Gd _1?x Fe₃ system increase with x parameter. The Mössbauer spectra are analyzed using four sextets, corresponding to three crystallographically (b, c, h) and four magnetically (b, c, h₁, h₂) inequivalent sites for iron. The mean hyperfine magnetic field increases with increase of the Gd concentration     

Mössbauer Study of the Fe3B/Nd2Fe14B Nanocomposite Magnet by the Addition of Co

The addition of Co to Nd₄Fe_77.5–x Co _x Hf_0.5Ga_0.5B_18.5 (0x5) was found to enhance the magnetic properties of Fe₃B/Nd₂Fe₁₄B nanocomposite magnets. The enhancement resulted from the fact that Co tends to retard the formation of Fe₃B from the amorphous matrix but to accelerate that of Nd₂Fe₁₄B. The decreased interval between the crystallization temperature of Fe₃B and Nd₂Fe₁₄B led to a uniform grain size distribution of both phases during the annealing treatment. The additive Co was confirmed to partition mainly to Nd₂Fe₁₄B crystals rather than to Fe₃B which was traced by XRD and Mössbauer spectroscopy as well. About 72 vol.% of Fe₃B, 27 vol.% of Nd₂Fe₁₄B, and a small amount of Fe around 1 vol.%, respectively, were found to form. However, the volume fraction of each phase did not vary by the addition of Co up to 5 at.%.     

Regulating element distribution to improve magnetic properties of sintered Nd–Fe–B/Tb–Fe–B composite magnets

Nd content was varied in Nd_(13.2-x)Fe_(80.8+x)B_6(x = 0, 0.5, 1, and 1.5) to optimize the magnetic properties of sintered Nd–Fe–B/Tb–Fe–B composite magnets, which were prepared by mixing 9 g of Nd–Fe–B with 1 g of Tb_(17)Fe_(75)B_8 powder.In conventional magnets, by reducing Nd content, the coercivity of 10.4 kOe in Nd_(13.2)Fe_(80.8)B_6 decreases to 7.2 kOe in Nd_(12.2)Fe_(81.8)B_6; meanwhile, in Nd–Fe–B/Tb–Fe–B magnets the coercivity does not decrease when reducing Nd content.In the intergranular phase, the Tb content increases owing to the reducing Nd content of the Nd–Fe–B alloy in the sintered composite magnets.Therefore, the excess Tb in Tb_(17)Fe_(75)B_8 enters the intergranular phase, and more Tb atoms can substitute for Nd at the grain boundary of the Nd–Fe–B phase, leading to a more significant increase in coercivity.The remanence increases with reducing Nd content, and the energy product of 39.1 MGOe with a high coercivity of 21.0 kOe is obtained in Nd_(12.2)Fe_(81.8)B_6/Tb_(17)Fe_(75)B_8 magnets.These investigations show that magnetic properties can be further improved by regulating the element distribution in sintered composite magnets.