Nanocrystalline alloys of Fe_{86.5}Zr_{6.5}Cu_1B_6 and Fe_{40.5}Co_{40.5}Nb_7B_{12} were measured by the Mössbauer spectrometry in the weak external magnetic field of 0.5 T. In these conditions the most sensitive parameters of the Mössbauer spectra are the intensities of 2nd and 5th lines and the values of internal magnetic field showed rather small changes. The amorphous part of the sample is more sensitive to the external influence than the nanocrystalline one. The behavior of nanocrystalline alloys under weak external magnetic field was analyzed within influence of interparticles interactions on the magnetic parameters.
Nanocrystalline alloy of FINEMET and NANOPERM-type were studied by the Mössbauer spectroscopy after atmospheric corrosion up to 10 months. Corrosion process has an influence on the magnetic microstructure, which reflects at the Mössbauer parameters as a change in direction of net magnetic moment, intensity, and distribution of internal magnetic field. During corrosion process the most occurring tendency was the rotation of net magnetic moment out of the ribbon plane. This behaviour might result from the internal stress produced during corrosion treatment. The observed changes in the average hyperfine field and shape of its distribution indicated the changes of the microscopic magnetic properties induced by corrosion damage. These results are compared with radiation corrosion.
Nanocrystalline (Fe_{1-x}Ni_{x})_{81}Nb_{7}B_{12} (x=0, 0.25, 0.5, 0.75) and Vitroperm alloys were studied by Mössbauer spectroscopy after neutron irradiation at fluences of 10^{16} n/cm^{2} and 10^{17} n/cm^{2}. From structure analyses, we have identified ferromagnetic bcc-FeNi in nanocrystalline state and partly paramagnetic (Fe-Ni)_{23}B_{6} phase. Neutron irradiation had an influence on the magnetic microstructure, which is manifested in the change of the Mössbauer parameters, such as the direction of net magnetic moment, the intensity of internal magnetic field and the volumetric fraction. The results indicate that the changes of the microscopic magnetic parameters, induced by neutron irradiation, depend on iron and nickel content. Significant radiation damage started at neutron fluence of 10^{17} n/cm^{2}.
Nanocrystalline (Fe₃Ni₁)₈₁Nb₇B₁₂ alloy was irradiated by electron beams of doses up to 4 MGy. Irradiation had an influence on the magnetic microstructure of the studied alloys. It has manifested as a change in the mean orientation of local magnetization, intensity of the internal magnetic field, and distribution function of induction of internal magnetic field. All these parameters were determined from the measured Mössbauer spectra. The mean orientation of local magnetization was the most sensitive parameter. Structural changes were not identified by the Mössbauer spectroscopy and by X-ray diffraction. The results indicated that the changes of the microscopic magnetic parameters induced by irradiation depend on the phase composition. Intensity of internal magnetic field also contributes to resistivity of alloy against radiation.
Boron was partially substituted by phosphorus (3 at.%) in two Si-poor Fe-Nb-Cu-B-Si Finemets. Mostly non-significant changes were observed after vacuum annealing at 500°C, whereas equivalent Ar annealing resulted in significantly better soft-magnetic properties, which suffer from compressive surfaces stress. Possibly by hampering surface crystallization, the substitution eased the surfaces stress and reduced undesired off-axis anisotrophy at the cost of limiting the useful annealing temperature.
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