Nuclear relaxation in ferromagnetic amorphous alloys (FeNi)80B20 and (FeCo)80B20

A detailed study of the longitudinal and transverse¹¹b nmkr relaxation in (FeNi)₈₀B₂₀ and (FeCo)₈₀B₂₀ amorphous alloys in dependence on composition, frequency, and temperature has been undertaken. An explanation of results is attempted based on existing theories of NMR relaxation in ferromagnetic metals.     

Diffusion of Au and Cu in amorphous Fe80B20 and Fe82B18 alloys

Diffusion rates (D) of Au in two amorphous alloys, Fe₈₀B₂₀ and Fe₈₂B₁₈, and of Cu in amorphous Fe₈₂B₁₈ alloy were measured in the temperature range 546–645 K by using the technique of Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES), respectively. The diffusion of Au was found to be 3 to 6 times faster in Fe₈₀B₂₀ than in Fe₈₂B₁₈, though both the alloys had almost similar crystallization temperatures. The observed differences in the diffusion rates corroborate the fact that Fe₈₀B₂₀ has a more open structure than Fe₈₂B₁₈ as revealed from the reported values of the metal packing fractions of these two alloys. Also, the diffusivities of smaller sized Cu atoms (radius: 0.128 nm) were found to be higher by more than an order of magnitude than those of larger sized Au atoms (radius: 0.146 nm), suggesting a dependence ofD on the size of the diffusing species.     

Sputtered ductile amorphous Fe80B20 foils

Ductile amorphous foils of Fe₈₀B₂₀ have been sputter-deposited. We report here the results of structural and magnetic studies on these samples. Structural analysis shows slight differences between amorphous foils and ribbons. From the high-field measurements (H<15 T) the magnetic moment of Fe is estimated as 2.1±0.02 at 4.2 K in agreement with the value reported for ribbons. However, the magnetization is less temperature dependent in the foil, as compared to the ribbon. This result would indicate a lesser fluctuation in the exchange integralJ and hence lesser variations in the local environment of Fe. Finally the thermal stability is shown to be higher in the foils. It is suggested that sputtering technique could be used to prepare amorphous foils of large area for certain applications.     

Magnetovolume effects in Fe80-xNixCr20 alloys

Temperature and magnetic field dependences of the thermal expansion between 4 and 300 K and in fields up to 6 T were made on Fe_80-xNi_xCr₂₀ for 14⩽x⩽49 at%. This concentration range covered the regions in which the samples were antiferromagnetic, paramagnetic and ferromagnetic as well as spin glass and reentrant spin glass at low temperatures. We develop a method of determining the lattice contribution to the thermal expansion for such systems showing mixed magnetic behavior and analyze the present data accordingly. We find in ferromagnetic samples large magnetic contributions to the thermal expansion even at temperatures much higher than the Curie temperature. The field dependence of the lenght change shows behavior which is characteristic of the magnetic state of the system.     

Surface characterization of amorphous and crystallized Fe80B20

Recent studies of catalysis by amorphous metals have prompted an interest in their surface properties. We have utilized Auger electron spectroscopy, X-ray photoelectron spectroscopy and low energy alkali ion scattering to study the surface composition, electronic properties and topography of amorphous and crystallized Fe₈₀B₂₀ ribbons. The majorresults are that the surface stoichiometry is approximately that of the bulk, unaltered by segregation. Bulk crystallization results in the diffusion of impurities to the surface, but does not change the Fe/B ratio. A small shift in the B1s core level binding energy was observed on crystalline, annealed surfaces relative to amorphous or sputtered surfaces, but no shifts were observed in the iron core level energies. A weak feature due to the B2p levels was observed in the valence band spectra from sputtered surfaces. The surfaces exhibit atomic scale roughness which is not altered by bulk crystallization. Finally, there were no observable differences in the structure, composition or electronic properties between the two sides of the ribbons.     

Mössbauer spectroscopy of amorphous metglass Fe80B20

Amorphous metals (Metglass Fe₈₀B₂₀) have been studied by Mössbauer spectroscopy. In the analysis the radial distribution function of Bernal's liquid-structure model has been correlated with the distribution of magnetic hyperfine spectra.     

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.     

Relaxation effects in the Mössbauer hyperfine structure of amorphous Fe70Co10B20 at 125°C

A new approach was attempted in following the irreversible relaxation effects in the hyperfine structure of amorphous Fe₇₀Co₁₀B₂₀. Room temperature transmission⁵⁷Fe Mössbauer spectra were measured in the course of interrupted isothermal annealing. For the data fitting, a model of pseudo-three-dimensional distribution of correlated hyperfine parameters was adopted and the corresponding spectrum modelled by a FFT-based procedure. In addition to commonly used hyperfine parameters, the second order quadrupole splitting was also considered. The time dependences of the average magnetic and the second order quadrupole splittings show two relaxation stages interpreted as the relief of quenched-in stresses and the free volume shrinking.     

Structural relaxation and chemical decomposition in amorphous TM-M alloys

Small angle X-ray scattering experiments performed on amorphous two-component transition metal-metalloid alloys have shown that these materials decompose on annealing clearly before crystallization starts. This process influences the behaviour of physical properties in a similar way as structural relaxation does. To separate the two effects mainly composition dependent properties must be compared with others which are mainly sensitive to structural changes. In this paper it is shown that the ratio of the annealing-induced changes of the temperature coefficient of the resistivity and of the residual resistivity is determined by the underlying elementary process. The two values resulting for predominating structural relaxation and for predominating decomposition seem to be universal and are compatible with a theory of phonon-controlled conductivity in high-resistance conductors.     

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.     

Radio-frequency annealing effects in amorphous Fe40Ni40B20

The influence of radio frequency (rf) magnetic fields on the properties of amorphous Fe₄₀Ni₄₀B₂₀ was studied using Mössbauer spectroscopy. The measurements were performed with frequencies of 67 and 53 MHz and rf field intensity in the range of 1 to 12 Oe. The narrowing of the hyperfine spectra due to the rf field and the formation of rf sidebands were observed. The effect of instability and crystallization of the amorphous metal enhanced by the rf field at temperatures much lower than the crystallization temperature was observed.     

Magnetic properties of the amorphous alloy Fe80Er20

Amorphous Fe₈₀Er₂₀ alloys were prepared with the melt spinning technique. The ribbons were investigated by Mössbauer spectroscopy from room temperature to 4.2 K. A phase transition from the paramagnetic to the ferromagnetic phase could be observed. The temperature dependence of the internal magnetic field was measured. The correlations of the hyperfine parameters were determined from the 4.2 K spectrum.     

Mössbauer study of corrosion products formed on Fe80B20 and Fe40Ni40(MoB)20 amorphous alloys in an SO2-polluted atmosphere

ICEMS, XPS, XRD, and AES have been used to study the corrosion layers formed on two metallic glasses, Fe₈₀B₂₀ and Fe₄₀Ni₄₀(MoB)₂₀ (2605 and 2826 MB, Allied Company), exposed to an SO₂-polluted humid atmosphere. The iron-containing corrosion products are the same found for pure iron in the same environment, but different relative concentrations were clearly evidenced by ICEMS results. Elemental sulphur, Ni(OH)₂, and B(OH)₃, the latter enriched at the surface, were found by XPS, XRD, and AES.     

A combined NMR and Mössbauer study of SRO in Fe80B20−x C x,amorphous alloys

The short range order (SRO) of amorphous Fe₈₀B_20?xC_x (X=0, 2, 4, 7, 9) alloys has been investigated by means of Mössbauer effect (ME) and nuclear magnetic resonance (NMR). Both the amorphous samples and the samples annealed at lower temperatures (693–713K) for a short time (10 minutes) were used. The Mössbauer measurement shows that the experimental spectra of annealed samples consist of the subspectra of α-Fe and bct-Fe₃B for X=0, While of α-Fe, bct-Fe₃B and o-Fe₃ (B, C) for X=2, 4, 7, 9. Moreover, the relative intensities of the subspectra originating from o-Fe₃ (B, C) increases with carbon concentration. These results are consistent with those of NMR very well.     

Study of the structural relaxation and crystallization in amorphous Fe80P20 alloy by mössbauer effect

The structural relaxation and crystallization of amorphous Fe₈₀P₂₀ alloys have been investigated by Mössbauer spectroscopy. The result indicates that the process of the crystallization of Fe₈₀P₂₀ makes slow progress and it was occur from outside into inside. The amorphous alloys may be classified into six different stages from amorphous to crystalline state during annealing.