Effect of ionic irradiation on the pre-exponential factor of thermally activated crystallization in Co66Si16B12Fe4Mo2 metallic glass

In the present paper, we report the Meyer-Neldel relation between the pre-exponential factor and activation energy of non-isothermal crystallization of Co₆₆Si₁₆B₁₂Fe₄Mo₂ metallic glass. Differential scanning calorimeter (DSC) is employed to study the change in the above two kinetic parameters of the crystallization due to ionic irradiation at three different fluences with high-energy heavy ion; Ni¹¹⁺ of 150 MeV.     

Magnetic thermoelectric power of Fe20Ni60B10Si10 metallic glass

The magnetic contribution to the thermoelectric power was separated for the metallic glass Fe₂₀Ni₆₀B₁₀Si₁₀ which exhibits the ferro-paramagnetic transition at T_c = 455 K remarkably below the crystallization threshold T_x = 670 K. Results are compared with the predictions of the Kasuya theory.     

Modification of the saturation magnetostriction constant after thermal treatments for the Co58Fe5Ni10B16Si11 amorphous ribbon

A new method for measuring the magnetostriction constant has been developed. The resolution of this sensitive method allows to measure values of that constant as low as 10^-9. It has been found that after thermal treatments, the magnetostriction constant of the amorphous ribbon whose nominal composition is Co₅₈Fe₅Ni₁₀B₁₆Si₁₁ changes not only its absolute value but also its sign. The kinetics of this variation has also been studied and a mean value of the activation energy of 0.8 eV for the relaxation process was obtained. Such variations of the magnetostriction constant are discussed as produced by modifications of the short-range order during annealing.     

Magnetic anisotropy in Co73Mo2Si15B10 and (Co0.89Fe0.11) 72Mo3Si15B10 metallic glasses,induced by stress-annealing

Annealing temperature dependence of the stress-induced magnetic anisotropy in Co₇₃Mo₂Si₁₅B₁₀ (λ_s < 0) and (Co_0.89Fe_0.11) ₇₂Mo₃Si₁₅B₁₀ (λ > 0) metallic glass ribbons has been studied experimentally. The room temperature values of the induced anisotropy constants K depend strongly on the annealing conditions, and reveal a change of sign at annealing temperatures well below T_cryst. It is concluded that transient creep and steady-state creep at the elevated temperature give rise to compressive and tensile stresses, respectively, in the expression for the magnetoelastic coupling energy at room temperature.     

Microstructure evolution in the rapidly quenched Fe78Si9B13 ribbons

We report microstructure evolution in as-spun Fe₇₈Si₉B₁₃ ribbons under various wheel speeds (s), which was investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). With decreasing s, the volume fraction of the residual amorphous phase (V_a) in the as-spun ribbons decreases gradually, and the total exothermic heat of the crystallization in the DSC curves also decreases, but the ratio of the exothermic heat of the second crystallization to the first one is on the contrary. α-Fe is found in the ribbon with s of 32.9 m/s, while α-Fe, eutectic α-Fe+Fe₂B, and Fe₃Si phases are found in ribbons with s of 25.6 and 18.3 m/s. The phase precipitating behavior in cooling processes is well consistent with the annealing process in the literatures.     

Giant magnetoimpedance in amorphous (Co0.93Fe0.7)63Ni10Si11B16 glass-coated microwire

Giant magnetoimpedance (GMI) effect has been measured in a glass-coated amorphous (Co_0.93Fe_0.7)₆₃Ni₁₀Si₁₁B₁₆ microwire as a function of DC magnetic field and up to the frequency of 11 MHz. The sample shows single peak GMI characteristics within the whole range of frequency. The domain structure of the above sample has been changed by applying tensile stresses up to 603 MPa and current annealing with a DC current of 50 mA for various time durations, and the corresponding effect on GMI has been studied in detail. A maximum change of 8.85% in MI of the as-quenched sample has been observed around a frequency of 5.05 MHz. Application of an external tensile stress reduces the GMI value by increasing the inner core domain, whereas heat treatment of the sample enhances the same. The square-shaped magnetic hysteresis loop of the as-quenched sample helps us understanding the MI results.     

Quadratic temperature dependence of electron-phonon scattering in disordered V1−xPdx alloys

We report the results of a comprehensive study of weak localization and electron-electron interaction effects in disordered V_1−xPd_x alloys whose compositions are close to the (low T_c) A15 V₃Pd compound. Magnetoresistivity and zero field resistivity have been measured within the temperature range 1.5≤T≤300 K. The low-temperature resistivity obeys a law, which is explained by electron-electron interaction. We have determined the electron-phonon scattering time (τ_e-ph) for V_1−xPd_x alloys. Our results indicate an anomalous electron-phonon scattering rate obeying quadratic temperature dependence. This observation is interpreted by the existing theories of electron-phonon interactions.     

Structural and magnetic characterization of Co67Fe4Ni2Si15B12

 Soft magnetic properties of Co-based amorphous alloy of the composition Co₆₇Fe₄Ni₂Si₁₅B₁₂ have been investigated by isothermal heat treatment up to the conventional crystallization temperature. In the as-cast condition the Curie temperature of the sample is 272 °C and saturation magnetization is 74 emu/g. Magnetic properties undergo variation depending on the heat treatment temperature. For the heat treatment temperatures of around 420 and 490 °C, superior soft magnetic properties are obtained. For both the temperatures initial permeability, μ′ reaches value up to ten times the value of permeability in the as-received samples. Annealing effect on giant magneto-impedance has been observed for the current-driving frequencies of 4.5 and 6 MHz. Field dependence of magneto-impedance shows hysteresis at low field, which is related to the changes in the magnetization process of the sample.     

The magnetic susceptibility of hydrogen-doped partially crystalline (Zr76Ni24)1−xHx metallic glasses

The magnetizations of Zr₇₆Ni₂₄ metallic glass and hydrogen-doped partially crystalline (Zr₇₆Ni₂₄)_1−xH_x metallic glasses have been measured in the temperature range 10-300 K and magnetic fields up to 2 T for various dopant concentrations (x=0, 0.024, 0.043, 0.054). It is found that the samples are paramagnetic and magnetic susceptibility at room temperature, χ(300 K), shows a nonmonotonic behaviour upon hydrogenation. The values of χ(300 K) of the hydrogen-doped partially crystalline (Zr₇₆Ni₂₄)_1−xH_x metallic glasses are reduced with increase in hydrogen content up to x=0.043, whereas for x=0.054, an enhancement of χ(300 K) has been revealed. The magnetic susceptibility is weakly temperature dependent down to 110 K, below which an increase is observed. A shallow minimum exists between 90 and 120 K. The form and magnitude of the observed temperature dependence of the magnetic susceptibility are well accounted for by the sum of the quantum corrections to the magnetic susceptibility. Hydrogen reduces the electronic diffusion constant and influences strongly the quantum interference at defects, slowing down the spin diffusion and enhancing the magnetic susceptibility in the temperature range from 110 down to 10 K.     

Mössbauer study of a ferromagnetic metallic glass: Fe74Co10B16

Amorphous Fe₇₄Co₁₀B₁₆ (METGLAS 2605CO) has been studied in the temperature range of 77 K – 700 K by Mössbauer spectroscopy. Its crystallization temperature is found to be 665 ± 5 K and Curie temperature is estimated to be 760±10 K. The observed rapid decrease in reduced hyperfine fields can be explained well by Handrich's model for amorphous ferromagnets if one assumes a temperature dependent δ, a measure of fluctuations in the exchange interactions in such solids.     

Structure and electrical properties of SrO-borovanadate (V2O5)0.5(SrO)0.5−y(B2O3)y glassses

SrO-borovanadate glasses with nominal composition (V₂O₅)_0.5(SrO)_0.5−y(B₂O₃)_y, 0.0≤y≤0.4 were prepared by a normal quench technique and investigated by direct current (DC) electrical conductivity, inductively coupled plasma (ICP) spectroscopy, infrared (IR) spectroscopy and X-ray powder diffraction (XRD) studies in an attempt to understand the nature of mechanism governing the DC electrical conductivity and the effect of addition of B₂O₃ on the structure and electrical properties of these glasses. XRD patterns confirm the amorphous nature of the present glasses and actual compositions of the glasses were determined by ICP spectroscopy. The temperature dependence of DC electrical conductivity of these glasses has been studied in terms of different hopping models. The IR results agree with previous investigations on similar glasses and it has been concluded that similar to SrO-vanadate glasses, metavandate chain-like structures of SrV₂O₆ and individual VO₄ units also occur in SrO-borovanadate glasses. The SrV₂O₆ and VO_n polyhedra predominate in the low B₂O₃-containing SrO-borovanadate glasses as B substitutes into the V sites of the various VO_n polyhedra and only when the concentration of B₂O₃ exceeds the SrO content do BO_n structures appear. This qualitative picture of three distinct structural groupings for Sr-vanadate and Sr-borovanadate glasses is consistent with the proposed glass structure on previous IR and extended X-ray absorption fine structure (EXAFS) studies on these types of glasses. The conductivity results were analyzed with reference to theoretical models existing in the literature and the analysis shows that the conductivity data are consistent with Mott's nearest neighbor hopping model. Analysis of the conductivity data shows that they are consistent with Mott's nearest neighbor hopping model. However, both Mott VRH and Greaves models are suitable to explain the data. Schnakenberg's generalized polaron hopping model is also consistent with temperature dependence of activation energy. However, various model parameters such as density of states, hopping energy, etc. obtained from the best fits were not found to be in accordance with the prediction of the Mott model.     

Magnetic annealing and crystallization kinetics of the metallic glass Fe5Co70Si15B10

Magnetic annealing and crystallization kinetics of amorphous ribbons of Fe₅Co₇₀Si₁₅B₁₀ were studied. For a toroid stress-relieved at 365°C for 2 h, the anistropy energy K_u obtained by cooling in a magnetic field from 300°C was ≈1.1 × 10³erg/cm³ at room temperature. The reorientation of induced anisotropy of this toroid followed the equation for first-order kinetics closely, yielding an activation energy ΔE = 1.9 eV and a pre-exponential frequency factor v₀ = 3.2 × 10¹³s^-1. Anisotropy reorientation in a toroid partially stress-relieved at 220°C, although was clearly reversible during 8 cycles of isothermal annealing in tranverse and in longitudinal field, exhibited significant deviations from the equation for first order kinetics. Treating the data in terms of the equation for first order kinetics, a narrow spectrum of activation energy from 1.2 to 1.8 eV, with corresponding frequency factors from 1.8 × 10⁸ s^-1 to 5.6 × 10¹² s^-1, was obtained. The difference in behavior between the two samples is discussed in the light of concepts in structural relaxation recently proposed by T. Egami. Crystallization kinetics was studied on a DSC apparatus, using Kissinger's method. At 10 K/min heating rate, the temperature of incipient crystallization was found to be 770 K. The activation energies found were in the range 4.8–4.2 eV.     

Co-relation between pre-exponential factor and activation energy of non-isothermal crystallization for virgin and irradiated Fe78B13Si9 metallic glass

The present work shows the applicability of Meyer-Neldel relation between the pre-exponential factor and activation energy of non-isothermal crystallization of Fe₇₈B₁₃Si₉ metallic glass. Differential scanning calorimeter (DSC) technique is used to observe the variation in the above two kinetic parameters of the non-isothermal crystallization due to ionic irradiation at three different fluences with high-energy heavy ion Ni¹¹⁺ having energy 150 MeV.     

Influence of glass coating thickness and metallic core diameter on GMI effect of glass-coated Co68Fe4.5Si13.5B14 amorphous microwires

Influences of the size factors (glass coating thickness and metallic core diameter) of microwires on GMI effects of the glass-coated Co₆₈Fe_4.5Si_13.5B₁₄ amorphous microwires were investigated. The results indicated that the GMI effect of the microwires with the same glass coating thickness or the same metallic core diameter was initially increased to a peak and then decreased with an increase in the diameter or the thickness. The glass coating thickness and the metallic core diameter corresponding to the maximum GMI varied with metallic core diameter and glass thickness, respectively. The GMI effect of the microwires with the same geometric size varied remarkably under different cooling rates. Such effect was ascribed to the microstructural changes of the metallic core wire under different cooling rates. The influence of the glass coating thickness on the GMI effect of the microwire was attributed to the synthetical actions of crystallization enthalpy (degree of disorder) and the internal stress.     

A high resolution field ion microscopic study of Fe40Ni40B20 metallic glass imaged at liquid hydrogen temperature

Metallic glass Fe₄₀Ni₄₀B₂₀ is imaged at liquid hydrogen temperature in field ion microscope. Pair and angular distributions are obtained from the analysis of a large number of micrographs. The pair distribution is found to exhibit features typical of metallic glasses. The angular distribution agrees well with the theoretical distribution for Lennard-Jones glass obtained by Jacobaeus et al. The closer agreement achieved has been attributed to the better experimental conditions and the improved resolution of field ion microscope.     

Mössbauer spectroscopy studies of spin reorientations in amorphous and crystalline (Co0.2Fe0.8)72.5Si12.5B15 glass coated micro-wires

Thermo-gravimetric, differential scanning calorimetry and comprehensive ⁵⁷Fe Mössbauer spectroscopy studies of amorphous and crystalline ferromagnetic glass coated (Co_0.2Fe_0.8)_72.5Si_12.5B₁₅ micro-wires have been recorded. The Curie temperature of the amorphous phase is T_C(amorp) ∼730 K. The analysis of the Mössbauer spectra reveals that below 623 K the easy axis of the magnetization is axial-along the wires, and that a tangential or/and radial orientation occurs at higher temperatures. At 770 K, in the first 4 hours the Mössbauer spectrum exhibits a pure paramagnetic doublet. Crystallization and decomposition to predominantly α-Fe(Si) and Fe₂B occurs either by raising the temperature above 835 K or isothermally in time at lower temperatures. Annealing for a day at 770 K, leads to crystallization. In the crystalline material the magnetic moments have a complete random orientation. After cooling back to ambient temperature, both α-Fe(Si) and Fe₂B in the glass coated wire show pure axial magnetic orientation like in the original amorphous state. The observed spin reorientations are associated with changes in the stress induced by the glass coating.     

Low temperature resistivities of FexNi80-xP14B6 metallic glasses

The resistivities of six Fe_xNi_80-xP₁₄B₆ alloys have been measured between 1.5 and 50 K. It is found that the resistivity variations both below and above the resistivity minima depend on the transition metal composition. The room temperature coefficients of the resistivity indicate the existence of the magnetic contribution to the resistivity.     

Low temperature magnetization behavior in Co36Fe36Si3Al1Nb4B20 (at%) nanostructured alloy

The investigation addresses low temperature magnetization behavior in Co₃₆Fe₃₆Si₃Al₁Nb₄B₂₀ alloy ribbons in their as-spun as well as annealed state. Optimum heat treatment at 875 K led to nanocrystallization whereby bcc-(FeCo)SiAl nanoparticles were dispersed in an amorphous matrix as evidenced from transmission electron microscopy. Low temperature magnetization studies were carried out in the range 77-300 K. Using the method of mathematical fittings, magnetization extrapolated to 0 K was obtained. The dependence of the magnetization with respect to temperature of BT^3/2 was used to determine the Bloch coefficient “B” and spin wave stiffness constant “D”. Magnetic softening revealed by lowering in the coercivity in the optimum nanostructured state was also the cause of a drop in the stiffness constant. The range of exchange interaction given by D/T_C was higher in the nanostructured state compared to the as-spun amorphous state. The effect of nanocrystallization and the resulting ferromagnetic coupling was further evidenced by low temperature magnetization studies.     

A study on microstructure,magnetic properties and kinetics of the nanocrystallization of Fe40Ni38B18Mo4 metglass

This study has investigated the microstructure and magnetic properties of Fe₄₀Ni₃₈B₁₈Mo₄ at various degrees of crystallization from the amorphous state. TEM and XRD studies confirmed that phases forming after crystallization at temperatures around 414 and 522 °C were cubic (Fe, Ni, Mo)₂₃B₆ phase and FCC (Fe, Ni) solid solution. The growth behavior and morphology of the nanocrystalline phases have been studied as a function of time and temperature. Nanoparticles were lying in the size range of 10–20 nm and they were stable below 522 °C. Kissinger approach, Ozawa method and Yi Qun Gao method were employed to determine and compare the kinetic parameters of the crystallization processes. A growth mechanism of crystallizing phases was proposed on the basis of these results. Magnetic properties mainly coercivity and saturation magnetization of as-received and heat-treated samples were evaluated.     

Low temperature specific heat and thermal conductivity of bulk metallic glass (Cu50Zr50)94Al6

The low temperature specific heat and thermal conductivity of (Cu₅₀Zr₅₀)₉₄Al₆ bulk metallic glass have been studied experimentally. A low temperature anomaly in the specific heat is observed in this alloy. It is also found that in addition to Debye oscillators, the localized vibration modes whose vibration density of state has a Gaussian distribution should be considered to explain the low temperature phonon specific heat anomaly. The phonon thermal conductivity dependence on temperature for the sample does not show apparent plateau characteristics as other glass materials do; however, the influence of the resonant scattering from the localized modes on the lattice thermal conductivity is prominent in the bulk metallic glass at low temperatures.