High field magnetization and57Fe hyperfine field in amorphous RuxFe80−xB20 alloys

Magnetism in amorphous alloys of Ru_xFe_80–xB₂₀, 0 × 22 has been investigated using high field magnetization and Mössbauer spectroscopy. The average Fe hyperfine field in Ru₁₈Fe₆₂B₂₀ shows an anomalous rise at low temperatures. In Ru rich alloys a low field component appears in the hyperfine field distribution and the alloys do not saturate magnetically in 80 kG fields. It is inferred that their magnetic structure is non collinear and that antiferromagnetic exchange in the system increases with Ru concentration.     

Resistivity and magnetoresistance of Fe80B20 and Fe78B13Si9 amorphous glasses

Summary The electrical resistivity of Fe₈₀B₂₀ and Fe₇₈B₁₃Si₉ amorphous glasses as a function of temperature from 293 K down to 15 K was measured, and it was found to fit quite well with the model given by Cote and Meisel. Comparison between our resistivity measurements of Fe₈₀B₂₀ and others was made, where some differences were found. These resistivity differences are evidence for a variety of amorphous atomic arrangements of the samples. The longitudinal magnetoresistance of Fe₈₀B₂₀ and Fe₇₈B₁₃Si₉ at 293K and 77K was measured in a low magnetic field. The observed magnetoresistance shows a typical field dependence known for ferromagnetic materials.     

Effect of element substitution on nanostructure and hard magnetism of rapidly quenched Nd2Fe14B

The structural and magnetic properties of Nd₁₂Fe₈₂B₆ and Nd₁₀M₂Fe₈₂B₆ (M = Nb, Ti, Zr, Cr) alloys prepared using arc melting and melt spinning have been investigated. All the samples are found to crystallise with a tetragonal Nd₂Fe₁₄B phase without any alloy or elemental impurities. There is a small decrease in the unit cell volume of Nd₂Fe₁₄B due to transition metal (M) addition. The substitution of Nb and Ti refines and homogenises the nanostructure of the alloys, promoting intergrain exchange coupling leading to an increase in the remanence and energy product. For example, the remanence and energy product of Nd₁₂Fe₈₂B₆ and Nd₁₀Nb₂Fe₈₂B₆ are 8.4 kG and 15 MGOe, and 9.9 kG and 20 MGOe, respectively. The J(T) curves are similar to those of a single phase ferromagnetic material suggesting no segregation of ferromagnetic impurities. The observed structural and magnetic properties are consistent with the fact that the substitutional transition metal atoms occupy the Nd site of the tetragonal Nd₂Fe₁₄B crystal lattice. The improvement of magnetic properties of nanocrystalline Nd₂Fe₁₄B alloys with the decrease in Nd concentration may be beneficial for the application of this material in bonded magnets.     

Investigation of the magnetic characteristic of amorphous Fe40Ni40B20 and Fe6Co70Ni13Si7B4 foils by a magnetooptical method

Magnetic parameters, the local anisotropy field H_k, the effective field h related to the correlation radius, and the coercive force H_c, are determined for free and contact surfaces by investigating the magnetization curves of amorphous Fe₄₀Ni₄₀B₂₀ and Fe₆Co₇₀Ni₁₃Si₇B₄ foils by a highly-sensitive method of measuring the magnetooptical phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 49–52, November, 1989.     

Magnetic properties of amorphous MnxPd82−xGe18 alloys

Magnetoresistivity, magnetic, susceptibility and high field magnetization measurements were performed on the amorphous Mn _x Pd_82–x Ge₁₈ alloys for 1x7. These amorphous alloys were prepared by radio frequency (R. F.) sputtering using argon, depositing onto fused quartz substrates to a thickness of about 20 microns. The negative magnetoresistivity is approximately proportional to the square of the magnetization and the susceptibility obeying the Curie-Weiss law between 18 and 293 K. These results lead to the conclusion that a Kondo-type s-d exchange interaction exists in the amorphous Mn-Pd-Ge alloys and the d-d, spin correlation between magnetic atoms is, in general, weaker in the amorphous alloys than in the corresponding crystalline alloys.     

Characterizing structures in the Fe−Ni−B amorphous system

Amorphous alloys Fe₈Ni_80?XB₂₀ (x=20?60) and (Fe_0.5Ni_0.5)_100?yB_y (y=16?25) have been thermally treated between 300k and 800k in a differential scanning calorimeter (DSC). The phases have been determined using Mössbauer spectroscopy and x-ray diffraction methods. The crystallization temperatures, heats of crystallization and the crystallization products of the amorphous(a)-Fe?Ni?B system vary with the composition of Fe and with the that of B. Basing on the variations of these factors the short range order (sro) of the amorphous Fe?Ni?B alloy system is discussed.     

Low-temperature magnetic properties and susceptibility of amorphous Nd4Fe58.1Cr19.4B18.5 alloys

Low-temperature magnetic properties and the susceptibility of the amorphous Nd₄Fe_58.1Cr_19.4B_18.5 alloy were studied. The temperature dependence of magnetization exhibits T^3/2 behavior up to T/T_c=0.57. Spin-wave stiffness coefficient D=47 meV A² is much smaller than that of amorphous Fe₈₀B₂₀ alloys. The temperature dependence of the susceptibility χ₀ obeys Curie–Weiss law at T>1.5T_c. A larger effective magnetic moment per magnetic atom was obtained. The influence of Cr on low-temperature magnetic properties and the susceptibility was discussed.     

Local structure of Fe70Cr15B15 X-ray amorphous alloy

The local atomic and magnetic structure of Fe₇₀Cr₁₅B₁₅ X-ray amorphous alloy is studied by means of ¹¹B nuclear magnetic resonance (NMR) and ⁵⁷Fe Mössbauer spectroscopy. It is determined that Fe₈₅B₁₅ and Fe₇₀Cr₁₅B₁₅ X-ray amorphous alloys consist of microregions (nanocrystals) with short-range orders of t-Fe₃B and α-Fe phases. It was found out that chromium atoms in the Fe₇₀Cr₁₅B₁₅ X-ray amorphous alloy are evenly distributed in these two nanocrystals, forming t-(Fe,Cr)₃B and α-Fe(Cr) phases.     

Domain-wall energy in sintered Nd15Fe77B8 permanent magnet

From measurements of the magnetic domain widthsD versus grain thicknessL, we have determined the domain wall energy in the demagnetized state for a sintered Nd₁₅Fe₇₇B₈ magnet: = 56 erg/cm². Using this wall energy and the published magnetocry-stalline constantK ₁=4.9×10⁷ erg/cm³, we have calculated the exchange constantA=4.0×10^–6 erg/cm, domain wall thickness _B=89 Å, and the critical diameter for single domain particlesD _c=0.67 m.     

Superparamagnetic Relaxation in Nanocrystalline Fe80Zr7B12Cu1 Alloys

Nanocrystalline Fe₈₀Zr₇B₁₂Cu₁ alloys with different amounts and sizes of bcc precipitates were prepared by appropriate annealing of amorphous ribbons. The 6–10 nm ferromagnetic bcc granules are embedded in a residual amorphous tissue with a thickness at least 4 nm. Above room temperature superparamagnetic relaxation characteristic for small magnetic particles was observed with increasing temperature, as indicated by a significant increase in the width of the Mössbauer lines belonging to the bcc precipitates. It shows the absence of magnetic coupling which is stronger than the dipole-dipole interaction between the ferromagnetic nanoparticles.

     

Grain Boundary Diffusion and Linear and Non-Linear Segregation of Ag in Cu

Ag grain boundary (GB) diffusion was measured in the Cu-0.2at%Ag alloy in a wide temperature range from 473 to 970 K. The direct measurements of Ag GB diffusivity D ^alloy _gb under conditions of the Harrison C regime revealed that D ^alloy _gb is almost identical to D ^pure _gb determined earlier for Ag diffusion in high-purity Cu (Divinski, Lohmann, and Herzig, 2001). The penetration profiles determined in the Harrison B regime showed a complex, multi-stage shape. This diffusion behavior can be rationalized assuming that besides GBs significantly covered by segregated Ag atoms, some fraction of GBs remains almost free from Ag atoms in the studied temperature interval. The total amount of pure GBs drastically decreases with decreasing temperature. This hypothesis was proven by measurements of Ag GB diffusion in Cu near 5 bicrystals, which allowed us to analyze in detail the non-linear segregation of Ag in Cu GBs.     

EXAFS study of the atomic structure of amorphous Tb20Fe80

The atomic structure of amorphous Tb₂₀Fe₈₀ thin films has been studied by Extended X-ray Absorption Fine Structure (EXAFS) of both FeK and TbL _III absorption edges. The local site geometry around Fe atoms shows predominantly Fe nearest neighbors with an Fe-Fe distance distribution centered on 2.50±0.02 Å and a coordination number of 9.1±1. In contrast, the radial structure function (RSF) obtained at the Tb edge is broad and asymmetric. The peak in the RSF corresponds to a Tb-Fe near neighbor distance of 2.94±0.1 Å with no evidence for Tb-Tb nearest neighbor coordination. The width and the shape of the RSF suggest that the Tb-Fe atomic environment is anisotropic and strained probably as a consequence of the growth process. This distorted atomic environment is suggested to be responsible for the magnetic anisotropy in these alloys. Thermal annealing at 200 °C leads to reduction inK _u. We propose that this results from reordering of the Tb local environment such that the average structural anisotropy in the distribution is reduced. EXAFS data show that annealing at 400°C causes precipitation of bcc polycrystalline Fe. The addition of 7 at.% Au to the alloy prevents this recrystallization and preserves the amorphous state but does not prevent the structural relaxation which reducesK _u at lower temperatures.     

Disaccomodation phenomenon in Fe82B18-xCx and Fe82B18-xSix metallic glasses

The isochronal disaccomodation (DA) of the initial permeability was measured in Fe₈₂B_18-xC_x and Fe₈₂B_18-xSi_x metallic glasses in the temperature range from 77 to 600 K. An asymmetric isochronal spectrum with a single relaxation peak was observed on each studied glassy alloy. The peak shifts to the lower temperature side with increasing C content in Fe₈₂B_18-xC_x, whereas the influence of Si on the peak in Fe₈₂B_18-xSi_x is opposite to the effect of C. The kinet ic behavior of DA was examined and the activation energy spectrum was evaluated. The replacement of B by C gives rise to the reduction of the activation energy, whereas the addition of Si increases the energy. A clearly annealing effect on DA was observed on each examined alloy.     

Fe39.4－xCo40Si9B9Nb2.6Cux纳米晶合金的有效磁各向异性研究

采用多晶材料趋近饱和定律研究了非晶Fe_39.4-xCo₄₀Si₉B₉Nb_2.6Cu_x(x=0.5,1,1.5) 合金在不同温度纳米晶化后的有效磁各向异性常数〈K〉.结果表明， Cu含量较低(x=0.5)时，纳米晶粒较大并且在较低的退火温度(550℃)下析出硬磁相，〈K〉随退火温度T_a升高显著增加；随着Cu含量的增加，有效地细化了晶粒，并且抑制了硼化物的析出，〈K〉明显减小.讨论了〈K〉与晶粒尺寸D及初始磁导率的关系. 关键词： 纳米晶 有效磁各向异性 磁导率 FeCo基合金     

Correlations between hyperfine parameters of Fe−Ni-B amorphous metals

The correlations between fluctuations in the⁵⁷Fe Mössbauer hyperfine parameters of the amorphous alloys (Fe_0.5Ni_0.5)_100?x B _x (x=16, 18, 20, 22 and 25 at%) and Fe_yNi_80?y B₂₀ (y=20, 25, 40 and 60 at%) have been determined. Values of the correlation between the fluctuations of the isomer shift and the fluctuations of magnetic hyperfine field, μ_N 〈ΔHΔδ〉 together with published values on similar amorphous systems are compared with correlation values for related crystalline phases. The lack of characteristic values suggests that the correlation values do not allow a link to be made between local structural units in amorphous alloy and crystalline phases.     

Short range order of the amorphous Fe−B powders prepared by borohydride reduction

Ultrafine Fe?B amorphous alloy powders were prepared by reducing Fe²⁺ ions using KBH₄ and NaBH₄ in aqueous solution. Adjusting technological factors, the amorphous powders around the composition of Fe₆₅B₃₅ can be easily obtained, but in the vicinity of eutectic point (Fe₈₀B₂₀) a certain amount of α-Fe often appears in the samples. From the Mössbauer spectrum, the crystallization products of the Fe₆₃B₃₇ amorphous powder are α-Fe and Fe₂B phases. The measurement of¹¹B spin echo nuclear magnetic resonance (NMR) at 8K showed that Fe₂B-like and Fe₃B-like short range orders (SRO) exist in the amorphous powder of Fe₇₆B₂₄.     

Correlation between the optical properties of surface layers and bulk characteristics of amorphous alloys

Spectral ellipsometry was used to study surface layers of Fe₈₀ A ₅B₁₅ (A = Ti, V, Cr, Mn, Fe, Co, Ni) and Fe_78-x Ni_xSi₉B₁₃ (x = 0, 1, 4, 8, 16, 21 at. %) amorphous metal alloys obtained by melt spinning. The optical characteristics of the alloys were determined by solving the inverse problem of ellipsometry. A correlation between the optical properties of the surface layers of amorphous alloys and their thermal stability was found.     

Mössbauer study of the effect of preparation parameters in rapidly quenched Fe−Cr−P−C,Fe−Cr−B and Ni(57Fe)P amorphous alloys

Mössbauer spectroscopy was used to get information about the effect of preparation parameters (quenching rate, temperature and time of solution treatment of melt) on the structure of rapidly quenched Fe₇₀Cr₁₀C₇P₁₃, Fe₇₉Cr₁₅B₁₅ and Ni₈₀ ⁵⁷Fe₁P₁₉ amorphous alloys. We have found smaller but measurable thickness dependent changes in the average Mössbauer parameters and in the hyperfine field distribution of Fe₇₀Cr₁₀C₇P₁₃ samples than those observed in Fe₇₀Cr₁₀C₁₀P₁₀ amorphous alloys [3]. On the other hand, differences were found in the hyperfine field distribution of very rapidly quenched Fe₇₀Cr₁₀C₇P₁₃ alloys with increasing time of solution treatment of melt. Changes in the average parameters and in the quadrupole splitting distribution were also observed with variation of thickness as well as of temperature of melt in the Fe₇₀Cr₁₅B₁₅ and Ni₈₀(Fe)P₁₉ samples, respectively. The finding can be interpreted in terms of changes in the short range order due to different preparation conditions.     

Structural relaxation effects on the hyperfine parameters in Fe80B20 amorphous alloys

We have studied the influence of the relaxation effects on the different kinds of short range order structures which can be distinguished inFe ₈₀ B ₂₀ amorphous alloys by Mössbauer spectroscopy. The analysis of the distribution function of the hyperfine fields gives results on the variations of the chemical and topological short-range orders in good agreement with those known in literature. Attempt to give quantitative results is made.     

<Superscript>57</Superscript>Fe NMR study of amorphous and rapidly quenched crystalline Fe-B alloys

Amorphous and crystalline Fe-B alloys (5–25 at % B) were studied using pulsed ⁵⁷Fe nuclear magneticr esonance at 4.2 K. The alloy samples were prepared from a mixture of the ⁵⁷Fe and ¹⁰B isotopes by rapid quenching from the melt. In the microcrystalline Fe-(5–12 at %) B alloys, the resonance frequencies were measured for local states of ⁵⁷Fe nuclei in the tetragonal and orthorhombic Fe₃B phases and also in α-Fe. The resonance frequencies characteristic of ⁵⁷Fe nuclei in α-Fe crystallites with substitutional impurity boron atoms in the nearest neighborhood were also revealed. In the resonance frequency distribution P(f) in the amorphous Fe-(18–25) at % B alloys, there are frequencies corresponding to local Fe atom states with short-range order of the tetragonal and orthorhombic Fe₃B phases. As the boron content decreases below 18 at %, the P(f) distributions are shifted to higher frequencies corresponding to ⁵⁷Fe NMR for atoms exhibiting a short-range order of the α-Fe type. The local magnetic structure of the amorphous Fe-B alloys is also considered.