Simultaneous variations of microstructure and magnetic properties of Ni58Fe12Zr20B10 nanostructure/amorphous alloy prepared by mechanical alloying

This study aims to evaluate magnetic and micro-structural properties of amorphous/nanocrystalline mechanically alloyed Ni₅₈Fe₁₂Zr₂₀B₁₀ powders with ball-milling time up to 190 h. Structural, micro-structural and thermal evaluations of the milled powders were carried out by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and differential scanning calorimetry (DSC) methods. Magnetic properties were also measured by a vibrating sample magnetometer (VSM) instrument. Results showed that the amorphous phase reached maximum value of 95% and the crystallite size was about 3 nm at the end of the milling. Magnetization saturation (M_s) decreased slightly and coercivity (H_c) reached to the highest value at 72 h of the milling time. At the 190 h of milling, the coercivity and saturation magnetization reached 18 Oe and 20 emu/g, respectively. While, after an appropriate amount of heat treatment, these two variables became approximately 2 Oe and 32 emu/g.     

Microstructure and magnetic properties of bulk amorphous and nanocrystalline Fe61Co10Zr2.5Hf2.5Nb2W2B20 alloy

The microstructure and magnetic properties, i.e. the initial magnetic susceptibility, its disaccommodation, core losses and approach to ferromagnetic saturation of the bulk amorphous and partially crystallized Fe₆₁Co₁₀Zr_2.5Hf_2.5Nb₂W₂B₂₀ alloy are studied. From X-ray, Mössbauer spectroscopy and electron microscopy studies we have stated that all samples in the as-quenched state are fully amorphous. However, after annealing the samples at 850 K for 30 min the crystalline α-FeCo grains embedded in the amorphous matrix are found. Moreover, from Mössbauer spectra analysis we have stated that the crystalline phase in those samples exhibits the long-range order. The alloy in the as-quenched state shows good thermal stability of the initial magnetic susceptibility. Furthermore, the intensity of the magnetic susceptibility disaccommodation in the rod is lower than in the ribbon. It is due to low quenching rate during the rod preparation which involves the reduction of free volumes. From the analysis of the isochronal disaccommodation curves, assuming the Gaussian distribution of relaxation times, we have found that activation energies of the elementary processes responsible for this phenomenon range from 1.2 to 1.4 eV. After the annealing of the samples the initial susceptibility slightly enhances and disaccommodation drastically decreases. From high-field magnetization studies we have learned that the size of structural defects depends on the quenching rate (the shape of the samples) and changes after annealing.     

Magnetization behavior and magnetocaloric effect in bulk amorphous Fe60Co5Zr8Mo5W2B20 alloy

Microstructure by X-ray diffraction and Mössbauer spectroscopy, and isothermal magnetic entropy changes in the bulk amorphous Fe₆₀Co₅Zr₈Mo₅W₂B₂₀ alloy in the as-quenched state and after annealing at 720 K for 15 min are studied. The as-cast and heat treated alloy is paramagnetic at room temperature. The quadrupole splitting distribution is unimodal after annealing indicating the more homogenous structure in comparison with that for the as-cast alloy. Curie temperature slightly increases after annealing from 265±2 K in the as-quenched state to 272±2 K and the alloy exhibits the second order magnetic phase transition. The maximum of isothermal magnetic entropy changes appears at the Curie points and is equal to 0.30 and 0.42 J/(kg·K) for the alloy in the as-quenched state and after annealing, respectively. In the paramagnetic region the material behaves as a Curie-Weiss paramagnet.     

Cu60Zr30Ti10非晶合金弛豫和晶化过程的小角X射线散射研究

应用小角X射线散射技术研究了Cu₆₀Zr₃₀Ti₁₀非晶合金从300到813 K之间微结构的演化情况.发现在淬火状态下Cu₆₀Zr₃₀Ti₁₀非晶合金中存在直径30 nm左右的富Cu区.非晶的结构弛豫包括573 K之前的低温结构弛豫和573 K到玻璃转变温度的高温结构弛豫，弛豫的结果是产生含有有序原子团簇的富Cu区，这些有序原子团簇的富Cu区是随后晶化过程中晶核产生的基础.Porod曲线分析表明，晶化生成的纳米体心立方CuZr相和基体之间有明锐的界面. 关键词： 小角X射线散射 非晶合金 结构弛豫 晶化     

Studies of the relaxed amorphous phase in the Fe80Nb6B14 alloy

The paper presents measurements of magnetic permeability, magnetic after-effects, magnetostriction, DSC and XPS for the Fe₈₀Nb₆B₁₄ amorphous alloys preliminary annealed for 1 h at temperatures ranging from 300 to 770 K. It was shown that annealing out of free volume and internal stresses causes a decrease of magnetostriction coefficient and leads to the formation of the energetically stable relaxed amorphous state. The XPS spectra show local fluctuation of boron density. This effect was attributed to the formation of small iron clusters—the characteristic feature for the relaxed amorphous phase.     

Medium range ordering and some magnetic properties of amorphous Fe90Zr7B3 alloy

High-resolution electron microscopy (HREM) reveals in the as-quenched Fe₉₀Zr₇B₃ alloy the existence of medium range ordered (MRO) regions 1-2 nm in size. Transmission Mössbauer spectroscopy confirms that these regions are α-Fe MRO ones. Above the Curie point of the amorphous phase (T_C=(257±2)K) they behave like non-interacting superparamagnetic particles with the magnetization decreasing linearly with the temperature. For these particles the average magnetic moment of 390μ_B and the average size of 1.7 nm, in excellent agreement with HREM observations, were estimated. The maximum of the isothermal magnetic entropy change at the maximum magnetizing field induction of 2 T occurs at the Curie temperature of the amorphous phase and equals to 1.05 Jkg⁻¹ K⁻¹. The magnetic entropy changes exhibit the linear dependence on the maximum magnetizing field induction in the range 0.5-2 T below, near and above T_C. Such correlations are attributed to superparamagnetic behavior of α-Fe MRO regions.     

非晶Fe73.5Cu1Nb3Si13.5B9合金激光纳米化的超精细结构研究

在CO₂激光功率为50—300W、扫描速度为20mm/s、激光散光斑为20mm照射条件下 ，诱导非 晶Fe_735Cu₁Nb₃Si_135B9带中发生结构重组，产生定量纳米α-F e(Si)晶相形成双相组织结构材料. 利用穆斯堡尔谱研究了非晶Fe_735C u₁Nb₃Si_135B₉合金激光纳米化的 超精细结构. 实验结果表明，激光诱导非晶 Fe_735Cu₁Nb₃Si_135B ₉纳米化后，其超精细磁场的分布随 着激光功率变 化由单峰向双峰变化，在高功率辐照时， 出现了双峰分布，并且峰位向高场移动. 高激光 功率辐照非晶Fe_735Cu₁Nb₃Si_{135B9合金纳米晶化相有四种超精细结 构，即2个超精细磁场较小的初晶相和2个超精细磁场较大的纳米晶化相. 其中超精细磁场较 大(17—25MA/m)的α-Fe(Si)相为DO3结构. 关键词： 激光 纳米晶α-Fe（Si) 735}Cu₁Nb< sub>3Si_135B₉')" href="#">非晶Fe_735Cu₁Nb< sub>3Si_135B₉ 超精细结构 超精细磁场     

Low-frequency alternative-current magnetic susceptibility of amorphous and nanocrystalline Co60Fe20B20 films

This investigation experimentally studies the low-frequency alternating-current magnetic susceptibility (χ_ac) of amorphous and nanocrystalline CoFeB films by measuring the magnetic field established by passing currents of various frequencies through such films of various thicknesses (t_f). A CoFeB film is sputtered onto a glass substrate with t_f from 100 Å to 500 Å under the following conditions: (a) As-deposited films were maintained at room temperature (RT) and (b) films were post-annealed at T_A=150 °C for 1 h. The samples thus obtained are analyzed in a magnetic field that was generated by an alternating current (AC) at various frequencies from 10 Hz to 25,000 Hz. The experimental results demonstrate that the χ_ac declines as the thickness of the as-deposited sample and the post-annealed sample (T_A=150 °C) increases because the lower coercivity (H_c) of thinner CoFeB films is similar to a soft magnetic characteristic and is associated with a higher χ_ac value. The best χ_ac value is obtained at a thickness of 100 Å under both conditions. The χ_ac value of the post-annealed sample exceeds that of the RT sample at thicknesses from 100 Å to 500 Å because the magneto crystalline anisotropy of the post-annealed sample yields the highest χ_ac value at the optimal resonance frequency (f_res), at which the spin sensitivity is maximal. The X-ray diffraction patterns (XRD) of as-deposited CoFeB films reveal their amorphous structure. The XRD results for the post-annealed films include a main peak at 2θ=44.7° from the body-centered cubic (BCC) nanocrystalline CoFe that indicated a (110) textured structure. Post-annealing treatment caused that the amorphous structure to become more crystalline by a thermally driven process, such that the χ_ac value of the post-annealed sample exceeded that of the RT sample. This experimental result demonstrates that the χ_ac value decreased as the thickness of the thin film increased. Finally, the CoFeB thin films had the best χ_ac at low frequency (<50 Hz) following post-annealing treatment. The results obtained under the two conditions indicate that the maximum χ_ac value and the optimal f_res of a 100 Å-thick CoFeB thin film were 1.6 and 30 Hz, respectively, following post-annealing at T_A=150 °C for 1 h, suggesting that a 100 Å-thick CoFeB thin film that has been post-annealed at T_A=150 °C can be utilized as a gage sensor and in transformer applications at low frequencies.     

Superconductivity and electrical resistivity of amorphous Nb75Ge25 and Nb80Si20 after heavy ion irradiation at low temperature

Low temperature irradiation of thin films of Nb₇₅Ge₂₅ (T_c = 3.2 K) and Nb₈₀Si₂₀ (T_c = 4.7 K) with 20 MeV sulfur ions leads to an increase of T_c of about 0.5 K and a decrease of ? of about 1.5 to 3.5%. Annealing up to room temperature partly restores the initial values. Qualitatively the results can be explained by irradiation induced smearing of the structure factor, which is partially recovered by annealing.     

Medium-range structural order in liquid Ni20Al80 alloy: Experimental and molecular dynamics studies

In this Letter, structural properties of liquid Ni₂₀Al₈₀ have been studied through molecular dynamics (MD) simulations, and results agree well with X-ray experiments. The prepeak in the structure factor manifests the existence of medium-range structural order (MRSO) in liquid Ni₂₀Al₈₀. Analyses in MRSO reveal the dominance of ideal icosahedra and defective icosahedra which, furthermore, form clusters and share common atoms.     

Structural evolution of nanocrystalline/amorphous Fe/Ni75B25 multilayers: temperature dependence of electrical resistivity

X-ray specular-reflectivity measurements have been carried out on nanocrystalline/amorphous Fe/Ni₇₅B₂₅ multilayer films which were sputter-deposited on Si substrates, to investigate the evolution of interface roughness and the correlation between structure and transport properties. A significant interface roughness correlation with increasing Fe/NiB layer repetition was observed. The investigated films indicated a temperature dependent high electrical resistivity—10⁴ μΩ-cm at 10 K and 10³ μΩ-cm at 300 K—with a semiconductor-metal transition like behavior. Selected area electron diffraction revealed the presence of crystalline bcc Fe phase and NiB in amorphous state. The structural and transport properties of the multilayers are discussed.     

Effects of nickel on the crystallization of Zr70Cu20Ni10 amorphous alloy

Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) are employed to investigate the effects of nickel on the crystallization of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy. We have found that the crystallization process of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy is strongly influenced by the addition of nickel. Addition of 10 at% Ni to the Zr₇₀Cu₃₀ amorphous alloy makes the crystallization process proceed from a single-stage mode to a double-stage mode. The activation energy for crystallization of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy is calculated to be about 388kJ·mol^-1 on the basis of the Kissinger equation. The effects of nickel on the crystallization of the amorphous Zr₇₀Cu₂₀Ni₁₀ alloy are discussed in terms of the genetics of metals.     

Electrical resistance and magnetoresistance of amorphous alloys Gd67Co33 and Pd80Si20

In search for structural contributions to the low temperature anomaly we report high resolution resistance and magnetoresistance measurements ($\text{0.02}\text{K}\text{? T ? 20}\text{K}$) of amorphous splats of Gd₆₇Co₃₃ and Pd₈₀Si₂₀. For both alloys, the resistivity ?(H = 0, T) has a minimum at T ～ 10 K and increases with decreasing T. The ferromagnetic Gd₆₇Co₃₃ shows a strong negative field dependence of $\text{Δ?}\text{?(0)}$, saturating at H ～ 2T for T = 4.2 K but no measurable change in $\text{??}\text{?}\text{T}$ below 10 K is observed.The diamagnetic Pd₈₀Si₂₀ exhibits a positive field dependent magnetoresistance $\text{[Δ?}\text{?(0)]}\text{(}\text{H}\text{)}$ at low temperatures. Additionally, a field dependent part in $\text{??}\text{?}\text{T}$ is found which is probably due to paramagnetic impurities (～ 1 ppm Fe). However, there is also a field independent contribution in the amorphous state of Pd₈₀Si₂₀, which vanishes after crystallization. We attribute this to non-magnetic scattering induced by the disordered structure.     

Electrodeposition and characteristics of Ni80Fe20/Cu composite wires

Electrodeposited Ni₈₀Fe₂₀/Cu composite wire has significant advantages over amorphous wire as sensing element for weak magnetic field sensors, such as orthogonal fluxgate sensors, due to its non-ferromagnetic and conductive core structure. In this study, the key processing parameters are investigated, including electrodeposition current density, duty cycle, electrolyte solution, pH value, applied magnetic field, effect of seeded layers, and post annealing.     

Influence of milling time on the structural, microstructural and magnetic properties of mechanically alloyed Ni58Fe12Zr10Hf10B10 nanostructured/amorphous powders

This paper investigates structural, microstructural and magnetic properties of amorphous/nanocrystalline Ni₅₈Fe₁₂Zr₁₀Hf₁₀B₁₀ powders prepared by high energy milling. Ball milling of Ni, Fe, Zr, Hf and B leads to alloying of the element powders at 120 h. The results show that at 190 h the amorphous content is at the highest level and the grain size is about 2 nm. The magnetic measurements reveal that the coercivity and the saturation magnetization reach about 20 Oe and 30 emu/g at 190 h and become approximately 5 Oe and 40 emu/g after a suitable heat treatment, respectively.     

Patterning of amorphous and polycrystalline Ni78B14Si8 with a focused-ion-beam

The machining response of amorphous and crystalline Ni₇₈B₁₄Si₈ was investigated when structuring substrates using focused-ion-beam (FIB) milling. In particular, the sputtering yield as a function of the scan speed, and the effects of ion fluence and scan speed on the milled depth were studied. The ion fluence dependent evolution of the cross-sectional profiles of trenches was examined by atomic force microscopy (AFM). When milling amorphous Ni₇₈B₁₄Si₈, it was found that the sputtering yield first decreased with increasing the beam scan speed, then kept constant within the scan speed range, up to 710 nm/s, investigated in this work; it was also found that the milled depth was almost proportional to the ion beam fluence. The patterning of polycrystalline Ni₇₈B₁₄Si₈ resulted in anisotropic milling-rates due to the varying orientation of the grains in the material. The analysis of the profile evolution in both materials indicated that the surface finish of trenches was scan speed, ion beam fluence and scan strategy dependent. The study demonstrated that direct patterning by FIB could be used for producing masters in amorphous Ni-based alloys for injection moulding and hot embossing.     

Phase transition, structural and electrical properties of Pb(Zn1/3Nb2/3)O3-doped Pb(Ni1/3Nb2/3)O3-PbTiO3 ceramics prepared by solid-state reaction method

Phase pure perovskite (1−x−y)Pb(Ni_1/3Nb_2/3)O₃-xPb(Zn_1/3Nb_2/3)O₃-yPbTiO₃ (PNN-PZN-PT) ferroelectric ceramics were prepared by conventional solid-state reaction method via a B-site oxide mixing route. The PNN-PZN-PT ceramics sintered at the optimized condition of 1185 °C for 2 h exhibit high relative density and rather homogenous microstructure. With the increase of PbTiO₃ (PT) content, crystal structure and electrical properties of the synthesized PNN-PZN-PT ceramics exhibit successive phase transformation. A morphotropic phase boundary (MPB) is supposed to form in (0.9−x)PNN-0.1PZN-xPT at a region of x=32-36 mol% confirmed by X-ray diffraction (XRD) measurement and dielectric measurement. The MPB composition can be pictured as providing a “bridge” connecting rhombohedral ferroelectric (FE) phase and tetragonal one since crystal structure of the MPB composition is similar to both the rhombohedral and tetragonal lattices. Dielectric response of the sintered PNN-PZN-PT ceramics also exhibits successive phase-transition character. 0.64PNN-0.1PZN-0.26PT exhibits broad, diffused and frequency dependent dielectric peaks indicating a character of diffused FE-paraelectric (PE) phase transition of relaxor ferroelectrics and 0.40PNN-0.1PZN-0.50PT exhibits narrow, sharp and frequency independent dielectric peaks indicating a character of first-order FE-PE phase transition of normal ferroelectrics. The FE-PE phase transition of 0.56PNN-0.1PZN-0.34PT is nearly first-order with some diffused character, which also exhibits the largest value of piezoelectric constant d₃₃ of 462pC/N.     

The influence of hydrogen on the atomic distribution function and electrical resistance of amorphous chromium films

Electrical resistivity of amorphous chromium films (20–37 nm thick) deposited in a hydrogen atmosphere (P _{H 2}=8·10^–6–2·10^–4 hPa) onto a substrate cooled by liquid helium down to 2 K is measured, and electron-diffraction studies have been performed immediately after the quench condensation and after annealing to different temperatures up to 300 K. The preparation method employed permits a considerable hydrogen enrichment of the films to be reached. The maximum hydrogen concentration corresponds approximately to a stoichiometric composition of CrH. It is found that as the maximum concentration is approached the atomic distribution functionG(r) changes remarkably. The interatomic distances increase considerably (by 10%) and the atomic densities decrease. It is quite possible that amorphous chromium hydride is a final state with the maximum hydrogen concentration. For films with intermediate concentration,G(r) is found to vary substantially under annealing up to 90 K. The electron-diffraction and electronmicroscopic data, as well as the variations in resistivity due to annealing, suggest that with annealing up to 90 K, a hydrogen redistribution occurs in the amorphous films, initially homogenous in concentration. We observe also distinct indications of separation into phases with increased and reduced hydrogen contents.     

A simultaneous voltammetric and dilatometric study of hydrogen absorption in Pd and amorphous Pd80Si20

By simultaneously measuring the length change of a palladium electrode and the current through the electrolytical cell when a triangular voltage is applied across the cell, it is possible to distinguish between surface and bulk processes during hydrogen uptake in Pd. From a comparison of corresponding dilatograms and voltammograms of polycrystalline Pd with those of crystalline Pd and amorphous Pd₈₀Si₂₀, one concludes that the diffusion of hydrogen into the bulk of the samples takes place to a large extent along dislocation lines. Dilatometric and voltammetric measurements in magnetic fields up to 10T show that the absorption of well annealed Pd electrodes is increasing up to 1T and saturates at higher fields.