[en] The evolution from the amorphous to the nanocrystalline state has been studied on Fe_63.5Cr₁₀Cu₁Nb₃Si_13.5B₉ ribbons by means of high-frequency (30 kHz - 6 GHz) magneto-impedance measurements. Furnace annealing and DC Joule-heating have been applied and have been shown to induce similar effects to the samples, although current annealed ones display enhanced magneto-impedance properties

[en] The influence of DC Joule-heating treatment on magnetoimpedance response in Co₆₄Fe₂₁B₁₅ ribbons has been studied. Monitoring of electrical resistance during the thermal treatment, hysteresis loops measurements, X-ray diffraction (XRD) and Moessbauer spectroscopy were used to study the structural changes induced by the current-annealing technique. The connection between the magnetoimpedance response and microstructure has been studied in detail. Finally, the normalization effect on the maximum ΔZ/Z (%) ratio achieved due to the maximum magnetic field applied during the experiment has been considered

[en] Influence of anisotropy on magnetoimpedance (MI) effect in amorphous Co₆₇Fe₄Mo_1.5Si_16.5B₁₁ alloy prepared with varying quenching rate (QR) from melt and after annealing in transverse magnetic field has been studied. Intrinsic and induced anisotropies influence significantly the MI ratio and sensitivity to the applied field. Specimen prepared with lower QR in as-cast state as well as after field annealing shows sharp increase in MI ratio, attributed to the induction of transverse anisotropy in these specimens. The maximum MI ratio and sensitivity to magnetic field were obtained for the slower quenched sample and after transverse field annealing. The corresponding values of maximum MI ratio and the sensitivity to applied field are 121.5% and 19.5%/Oe, respectively

[en] The influence of Nb on nanocrystallization of amorphous Co₂₁Fe_64-xNb_xB₁₅ alloys has been studied. Increase in Nb content causes higher disorder in the atomic structure as well as in the spin texture of as-quenched alloys. The first step of crystallization leads to the formation of Fe₃Co phase embedded in residual amorphous matrix. In the second step of crystallization (FeCo)₂B phase is formed. Moessbauer measurements show that Fe₂B phase is not formed in the specimen with x=7, a non-magnetic phase is formed

[en] High-frequency (30 kHz-6 GHz) giant magneto-impedance (GMI) in glass-covered Co_83.2Mn_7.6Si_5.9B_3.3 amorphous wires has been studied as a function of annealing treatment. Normalization effects on GMI ratio have been studied by applying two different values of the maximum field

[en] X-ray diffraction, Moessbauer spectroscopy and magnetization measurements have been used to obtain complementary information about the changes in magnetic properties and short-range order in metallic glass ribbon of the nominal composition Co₆₇Fe₄Mo_1.5Si_16.5B₁₁ as a result of annealing under tensile stress and without this stress. The results obtained suggest that: (i) annealing results in an increased chemical short-range order in both the samples annealed with and without external stress, (ii) in the stress-annealed sample additional internal stresses are generated which are expected to be oriented preferentially along the external stress axis, (iii) the stress-induced anisotropy is expected to have contributions from both, anisotropic bond reorientation as well as magnetoelastic coupling of the anisotropic internal stresses generated during stress annealing with magnetostriction. However, since magnetostriction in the studied specimens was extremely small, the latter contribution seems to be negligible

[en] Radiation damage produced in amorphous Fe₇₀Si₉B₁₁C₂ by thermal neutron irradiation has been studied with an aim to get information about defects and other structural changes occuring in the system. Neutron irradiation results in surface crystallization of the specimen via radiation enhanced diffusion. Moessbauer studies give evidence against the formation of point-like defects on irradiation. (orig.)

[en] Quenching rate dependence of crystallization and magnetic properties of the nanocrystalline materials has been studied. It was found that higher quenching rates result in lowering of activation energy of crystallization and also the size of nanocrystalline grains. Coercive force of the specimen prepared with higher quenching rate is higher, which is attributed to higher surface to volume ratio in the specimens, resulting in a stronger domain wall pinning at the surface

[en] Structural defects produced by plastic deformation (cold rolling) in amorphous Fe₄₀Ni₄₀B₂₀ and Fe₇₈Si₉B₁₁C₂ have been studied through Moessbauer spectroscopy by monitoring changes in relative line intensities, which show marked variation after different roll reduction and subsequent isochronal annealing. Present studies clearly show that defects are created throughout the bulk of the specimen and not localized in shear bands only. Annealing behavior of defects shows that the defects completely anneal out in a narrow temperature range well below the crystallization temperature

[en] The effect of successive additions of Cu, Nb and Ta in amorphous Fe_77.5Si_13.5B₉ has been studied using X-ray diffraction and Moessbauer spectroscopy. Addition of Nb/Ta results in an increased near-neighbor distance as well as a decrease in topological order in the system. On the other hand, Cu addition results in a significant increase in the topological order. Addition of Cu does not significantly change the average hyperfine field, whereas, addition of Nb/Ta decreases the hyperfine field. Nb and Ta addition results in appearance of an additional hump in B_hf around 13 T due to Fe atoms with Nb/Ta near neighbors. Thermal annealing of the specimens at 390 deg. C results in changes in the short-range order, which are mainly chemical in nature