Stress-induced magnetic easy axis in amorphous Fe40Ni40P14B6

In a ribbon of amorphous Fe₄₀Ni₄₀P₁₄B₆ (Metglas 2826) the iron spins tend to be parallel to the plane of the ribbon, but the distribution of spin directions within the plane is nearly random. When a uniaxial tensile stress is applied to the ribbon the spins become almost completely aligned parallel to the applied stress. The technique of Mössbauer polarimetry was used to detect and measure this effect.     

Magnetic domain walls and pulsed magnetization reversal in amorphous Fe40Ni40P14B6 ribbon under tension

Magnetization reversal has been studied in long ribbons of Metglas 2826 under tension. At low fields propagating head-on domain boundaries of the Sixtus-Tonks type were observed. Measurements of their lengths, of order 20 to 50 cm, together with a simple magnetostatic model of their structure, yield values of the specific domain wall surface energy γ = 3.8 × 10^-8 σ^1/2 J m^-2 for tensile stress σ Pa. A value A= 5.6 × 10^-12 J m^-1 for the exchange constant follows. The low-fi eld mobility of these domain walls shows no evidence of relaxation damping at speeds below 1.2 m s^-1. The threshold field at which reverse domains nucleate is found to be proportional to the square root of the tension. At high fields (>200 A m^-1) the rough surface of the ribbon (the surface that came in contact with the quenching wheel during manufacture) reverses first and saturates at about the same time as the smooth surface begins to reverse and the volume reversal rate peaks. A simple quantitative model of the high field reversal process satisfactorily predicts both the surface and volume reversal rates. It yields a consistent value β_R = 14 kg m^-2s^-1 for the relaxation damping constant at wall speeds in excess of 13 m s^-1 and estimates the number of reversal nuclei in accord with Yagi and Anayama.     

Kinetics of induced magnetic directional order in a Fe40Ni40P14B6 amorphous alloy

The amorphous Fe₄₀Ni₄₀P₁₄B₆ alloy (Metglas 2826) has been annealed under magnetic field at several temperatures. The kinetics of induced magnetic anisotropy exhibits a broad spectrum (β = 4) of time constants; it obeys exactly an Arrhenius law with an activation energy of 1.74 ± 0.04 eV. These values are identical to those determined by resistivity measurements. This suggests the formation of short range directional order.     

Transversal magnetic field effect on Fe40Ni40P14B6 amorphous alloys

A study about the influence of an electric current flowing through an amorphous ribbon Fe₄₀Ni₄₀P₁₄B₆ has been done. It has been found that the magnetization curves are strongly influenced by such a current (from 0 up to 5000 Hz). Bitter patterns under the action of the current have been observed in order to gain a better knowledge of these effects. The wall energy has been evaluated from a simple model.     

Hyperfine field distribution in amorphous Fe40Ni40B20

From the Mössbauer investigation of amorphous Fe₄₀Ni₄₀B₂₀ and Fe₈₀B₂₀ alloys it was found that the substitution of Fe by Ni only shifts but does not influence the shape of the iron hyperfine field distribution contrary to that of crystalline f.c.c. Ni-Fe alloys suggesting a rather localized type of behaviour. The distributions of the linear combinations of isomer shift and quadrupole splitting are affected by this substitution.     

Existence of both spin-glass and mictomagnetic behaviour in the amorphous Fe10Ni70P14B6 alloy

Results of the accurate magnetization measurements performed on the amorphous Fe₁₀Ni₇₀P₁₄B₆ alloy in the temperature range 20–77 K in fields upto 1 kOe are reported. The complex magnetic behaviour exhibited by this alloy has been analyzed to show that a ferromagnetic ordering, occuring on a localized microscopic scale at a temperature T₀ very close to that given by the earlier Hall effect measurements, is accompanied by a superparamagnetic behaviour which below T₀ causes at first a spin-glass freezing of the magnetic spins when they interact with one another on a long range scale and then a mictomagnetic freezing of the giant superparamagnetic clusters at a lower temperature as a result of exchange interaction between their moments and the frozen spin-glass matrix. In addition, the present results, besides providing a clear physical insight into the widely different ordering temperatures obtained for this alloy from previous Mössbauer and resistivity measurements, on one hand and from our magnetization measurements on the other, strongly suggest a magnetic origin for the observed resistivity-minimum phenomenon. In conclusion, the present alloy represents a composition in the amorphous (Fe_xNi_1?x)₈₀P₁₄B₆ system well below the percolation limit.     

A Mössbauer study of amorphous Fe40Ni40B20

Amorphous Fe₄₀Ni₄₀B₂₀ (VITROVAC 0040) alloy has been investigated using ⁵⁷Fe Mössbauer Spectroscopy. The Curie temperature T_c is found to be well defined and is 695 ± 1 K. The quadrupole splitting just above T_c is 0.64 mm sec^?1. The crystallization temperature is 698 ± 2 K, close to but definitely above T_c. The average hyperfine field H_eff(T) of the glassy state shows a temperature dependence of $\text{H}{}_{\mathrm{<mtext>eff</mtext>}}\text{(0)[1 ? B}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{(T/T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{? C}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{(T/T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{? …]}$ indicative of the existence of spin wave excitations. The values of $\text{B}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{C}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ are found to be 0.40 and 0.06, respectively, for T/T_c ? 0.72. At temperatures close to T_c, H_eff(T) varies as (1 ? T/T_c)^β where β is one of the critical exponents and its value is found to be 0.29 ± 0.02.     

On the bimodality of the hyperfine field distribution in amorphous Fe32Ni36Cr14P12B6 alloy

The bimodality of the hyperfine field distribution in amorphous Fe₃₂Ni₃₆Cr₁₄P₁₂B₆ alloy reported by Chien et al. (Phys. Rev. B19 (1979) 81) is shown to be the result of the bimodality in the distribution of the values of the strengths of the bonds within the alloy. The bimodality in the distribution of the bond strength values arises from the presence of two types of dense random packed cells (one rich in Cr atoms and the other deficient in Cr) in the alloy.     

Galvanomagnetic effects in Fe40Ni40B20

Hall effect and magnetoresistance measurements on the amorphous ferromagnet Fe₄₀Ni₄₀B₂₀ are reported. Both properties are approximately independent of temperature (1.5–300 K) and related to magnetization. The extraordinary Hall coefficient is 3.5 × 10^?8 m³/As. The temperature dependence of the resistivity (1.5–30 K) is also reported.     

Anomalous temperature dependence of magnetization in polycrystalline Fe65Ni35 alloy

Magnetization at 0.3 and 140 Hz (0–10 Oe) and magnetic relaxation measurements were carried out in detail in the temperature range between 4.2 and 300 K for a polycrystalline Fe₆₅Ni₃₅ alloy. The typical temperature T_g and the magnetic field H_g which correspond to the anomalous temperature in χ-T curves and inflection field in σ-H curves, respectively, are summarized and a H-T diagram is obtained. A strong magnetic relaxation is observed along the H_g-T line. The temperature dependence of H_g is discussed by the thermal activation of 180° domain wall which is pinned strongly by the antiferromagnetic-like clusters below T_g. It is find that H _g is a linear function of T .     

Anomalous temperature dependence of magnetization in single-crystal Fe65Ni35 alloy

Magnetization (0–10 Oe) and magnetic relaxation measurements were carried out in the temperature range between 4.2 and 300 K for three picture-frame samples of Fe₆₅Ni₃₅ alloy whose edges were parallel to 100, 110 and 111, respectively. The typical temperature T_g and the magnetic field H_g which correspond to the anomalous temperature in the χ-T curve and inflection field in the σ-H curve, respectively are summarized and H-T_g and H_g-T diagrams are obtained. A strong magnetic relaxation is observed along the H_g-T line. The dependence of H_g on the crystallographic direction and on the temperature are discussed by the thermal activation process of the 180° domain wall which is pinned strongly by the antiferromagnetic clusters below T_g. The anomaly of magnetization of Fe₆₅Ni₃₅ alloy can be interpreted by the macroscopic picture of the coexistence of ferromagnetic and antiferromagnetic-like regions which may be caused by a statistical fluctuation of alloy composition.     

Crystallization kinetics of the Fe40Ni38Mo4B18 amorphous alloy

X-ray diffraction (XRD) and Mössbauer spectroscopy were used to study the annealing of the Fe₄₀Ni₃₈Mo₄B₁₈ amorphous alloy. The samples were isothermally annealed in the 858–878 K temperature range several times. Two crystalline phases were observed in the annealed samples: FeNi₃ and (Fe, Ni, Mo)₂₃B₆. Preliminary results indicate that assuming a linear relationship between the area under the main XRD peak associated with the FeNi₃ phase and its volume fraction, this can be fitted to a Johnson–Mehl–Avrami equation with an exponent n close to 1.0. Mössbauer results show a broad magnetic hyperfine field distribution in as-received samples and, consistent with XRD results, a sextet attributed to precipitates of FeNi₃ (B_hf=29.5 T) for long annealing times.     

A comparative study of FMR and Brillouin light scattering on amorphous Fe40Ni40B20

It is shown that magnetic surface mode frequencies in the amorphous ferromagnet Fe₄₀Ni₄₀B₂₀ measured using Brillouin light scattering depend upon the incident laser light intensity: presumably due to local heating of the specimen due to the concentration of the light flux into a focal spot only a few microns in diameter. Surface mode frequencies extrapolated to zero light intensity are shown to be consistent with magnetic parameters measured using ferromagnetic resonance at 35.731 GHz to within ±0.5 GHz for specimens of amorphous Fe₄₀Ni₄₀B₂₀. 0.5 GHz corresponds to a change of 0.17 kG in the saturation magnetization, 4πM_s.     

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.     

Magnetic hyperfine interaction and curie temperatures of amorphous (FexNi1−x)80P14B6

Amorphous magnetic glasses (Fe_xNi_1?x)₈₀P₁₄B₆ (0.1 ? x ? 1) have been studied by Mössbauer spectroscopy. At 4.2 K, well-defined and very similar spectra have been observed for samples with different Fe concentration. This suggests that the Fe hyperfine field distribution is insensitive to the amount of dilutant. The value of the average hyperfine field at 4.2 K increases with Fe concentration. A value of 232 kOe is obtained by extrapolating to zero Fe concentration. The relationship $\text{H}{}_{\mathrm{eff}}\text{(O) = (232 + 33}\text{μ}\text{)}\text{kOe}$, similar to that of crystalline Fe-Ni alloys describes the results. The values of T_c = 60 K, 234 K and 425 K have been determined for samples with x = 0.125, 0.25 and 0.375 respectively. The T_C vs. x relation suggests a critical concentration of x_c ? 0.1, above which ferromagnetism exists. By fitting the measured values of T_C to the results of a coherent potential approximation, exchange interaction temperatures of J_FeFe = 617 K, J_FeNi = 800 K and J_NiNi ? 0 K have been obtained.     

非晶态Fe13Ni67.2P4.5B15.3合金的临界现象

本文报道非晶态Fe₁₃Ni_67.2P_4.5B_15.3合金的磁化强度与温度和磁场关系的测量结果。在居里温度附近样品的磁特性符合二级相变规律,得到临界指数β=0.39±0.02,γ=1.56±0.06,δ=5.20±0.1,样品的居里温度T_c=(180.4±0.2)K。在实验误差范围内,临界指数β,γ,δ满足γ=β(δ-1)关系,在168—192K温度范围,实验数据满足二级相变的磁状态方程。当T>270K时,样品顺磁磁化率服从居里-外斯定律,由居里-外斯常数c计算出有效顺磁磁矩P_eff=3.19 μ_B。 关键词：     

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.     

Pressure dependence of the Curie temperature of amorphous Fe80-xMnxB20 alloys

The pressure effect on the Curie temperature of Fe_{80 - x}Mn_xB₂₀ (x = 6, 10 and 20) amorphous alloys has been investigated. The pressure derivative of the Curie temperature is very large. The model of itinerant electron ferromagnets and the pair interaction model were proposed to explain the experimental results.     

Magnetic force microscopy characterization of heat and current treated Fe40Ni38Mo4B18 amorphous ribbons

The domain structure of a magnetostrictive Fe₄₀Ni₃₈Mo₄B₁₈ amorphous ribbon has been studied using magnetic force microscopy (MFM) at room temperature. First, the evolution of the magnetic domain patterns as a function of the annealing temperature has been investigated. In samples heat treated at 250 and 450 °C for 1 h, a transformation from 90° to 180° domain wall has been clearly observed, while the sample heat treated at 700 °C for 1 h showed a magnetic phase fixed by the crystalline anisotropy. Additionally, the evolution of the magnetic domain structure by applying a DC current was recorded by the MFM technique. For current annealed samples at 1 A for 1, 30 and 60 min, a transformation between different domain patterns has been observed. Finally, in samples treated by the current annealing method under simultaneous stress, an increase of the annealing time gives rise to a different magnetic structure arising from the development of transverse magnetic anisotropy.     

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.