[en] Nanocrystalline soft magnetic materials (Fe_73.5Cu₁Nb₃Si_13.5B₉) are investigated at elevated temperatures where, by changing the crystalline volume fraction, the magnetic behavior changes from a regime dominated by hysteresis and relaxation effects (high crystallization levels) to a superparamagnetic behavior (low crystallization levels). At intermediate crystalline fractions, it is shown that the approach to saturation can be described by assuming, as it was previously done for the description of relaxation and hysteresis effects, the existence of clusters of coupled grains distributed in size

[en] In this work we studied temperature dependent magnetization processes in nanocrystalline Fe₈₆Zr₇B₆Cu₁. Ribbons produced by melt-spinning in air, were submitted to fast dc Joule heating in vacuum to induce a nanocrystalline α-Fe phase. In order to investigate the untrivial interplay between structural and magnetic properties, hysteresis curves were measured as a function of temperature, with particular attention to the magnetic hardening effect. Details of the magnetization process were analyzed by using the Preisach model of hysteresis. (orig.)

[en] The Barkhausen effect was experimentally investigated in sintered NdFeB hard magnetic materials. We analyzed noise properties along different magnetization curves. The jumps are associated with the reversal of single grains or of groups of grains. The comparison of noise properties along different curves gives experimental support to the nucleation-type picture. Jump-size distributions follow a power law with critical exponent 1.2, and with exponential cutoff depending on magnetization curve considered. The maximum cutoff size is correlated to a microstructural limit due to the average grain size

[en] Nanocrystalline Sm Fe Co, prepared by mechanically alloying the elementary powders and subsequent annealing (600 deg C/15 min), showed remanence enhancement (η=I_r/I_s=0.67) and H_c=18.6 k O e. Starting from the ac-demagnetized state, minor hysteresis loops were determined for magnetic fields up to 70 k O e for numerical calculation of the Preisach function p(h_c, h_u), where h_c and h_u are the elementary loop coercive field and interaction field. The numerically determined irreversible part of p(h_c, h_u) had a form indicating that it could be factored: p_irr(h_c, h_u) = (f(h_c) g(h_u), where f(h_c) and g(h_u) are log-normal and Gaussian distributions. An analytic expression for p(h_c, h_u) = f(h_c) g(h_u) + p_rev(h_c, h_u was fitted to experimental hysteresis curves. Some discrepancies were noted due to dynamic effects. The analytic expression for p(h_c, h_u) was used with the moving Preisach model to calculate Henkel plots. The experimental data were well represented with a moving parameter k = 1.4. (author)

[en] Time and temperature evolution of structural and magnetic properties of gradually devitrified NANOPERM-type alloy of composition Fe₈₄Nb_3.5Zr_3.5B₈Cu₁ has been studied using differential scanning calirometery (DSC), X-ray diffraction (XRD), Moessbauer spectroscopy and magnetic measurements. XRD and Moessbauer measurements reveal that thermal annealing (as a function of both time and temperature)-induced nanocrystallization leads to the formation of an Fe-rich bcc phase with a small amount of boron, while other non-magnetic elements like Nb, Zr and majority of B remain in the residual amorphous matrix. Grain diameter of the nanocrystalline phase ranges between 7 and 10 nm and their volume fraction ranges between 15% and 48%. Increase of annealing temperature as well as time affects the coercive field considerably. The lowest value of the coercive field, 6 Am^-1 (corresponding saturation magnetization value is 1.4 T), is obtained after annealing the sample at 530 deg. C for 1 h, ascribed to the increased exchange coupling between the nanograins