[en] As-cast ferromagnetic amorphous alloys of nominal composition (FeTM)₈₀B₂₀ have been studied by Moessbauer Spectroscopy, being TM one transition metal atom, Ni, Cr, Mo or Pd. A detailed analysis of the isomer shift, IS, and hyperfine field distribution, HFD, at Fe sites is reported in order to achieve some conclusions about the Chemical Short Range Order and the electronic structure in these alloys. HFD changes found in (FeNi)B for Ni rich concentrations suggest the existence of Fe atoms strongly interacting with Ni. Small amounts of Cr and Mo shift the HFD to lower values of hyperfine field, B_hf, while Pd enhances the B_hf

[en] Amorphous alloys of composition Fe₈₆Zr₇Cu₁B₆ have been prepared and annealed in the temperature range from 570 to 950 K, obtaining several degrees of nanocrystallization. Magnetic and Moessbauer measurements show the different phases that appear in the samples after the heating, and their percentage, depending on the annealing temperature. The Curie temperature of the amorphous phase is shown to remain almost unchanged during the crystallization. Moessbauer spectroscopy however, reveals subtle changes in the structure

[en] FeZrB metallic glasses present magnetic properties that are enhanced compared to the pure FeZr ones. In particular, a large increase of the Curie temperature has been found. Magnetic and Moessbauer measurements show a decrease of the spin-glass character and a parallel homogenization of the hyperfine-field distribution as the boron concentration increases. Resistivity versus temperature measurements show a change in behaviour with B content: in the samples with small amounts of boron, a minimum in the resistivity versus temperature curves appears near the Curie temperature, while samples with high boron content show a low-temperature minimum, characteristic of most metallic glasses. The analysis of the results suggests that the evolution of the magnetic behaviour is related to changes in the density of states at the Fermi level, rather than to changes in the Fe-Fe distances. This is in agreement with published data on the specific heat of FeZr and FeB glasses. The influence of boron is shown to greatly enhance the weak itinerant ferromagnetism of FeZr glasses, leading to stronger ferromagnetic behaviour. The characteristic features of the resistivity are analysed in terms of localization effects on the conduction electrons, which extend to higher temperatures in the low-boron-content alloys. (author)

[en] Room temperature X-ray absorption spectra on Fe K-edge have been performed in Fe_100-x-yZr_xB_y and Fe₈₆Zr₇Cu₁B₆ alloys (x=7, 7.7, 9; y=0, 2, 4, 6). Fe-Fe coordination number and interatomic distances do not change in any sample. However, small changes in the Fe-Zr short range order, which could explain the evolution of the magnetic properties, have been observed. (orig.)

[en] Moessbauer measurements have been performed on amorphous and nanocrystalline alloy ribbons of nominal composition Fe₈₆Zr₇Cu₁B₆. The nanocrystalline samples were obtained by annealing the as-quenched alloy at different temperatures in the range between 650 and 870 K. Moessbauer spectra of the as-quenched amorphous sample have been recorded at 77 K, room temperature and above the Curie temperature (∼ 330 K) at 360 K. We have also performed Moessbauer measurements at room temperature in the nanocrystalline alloys to characterize the phases that appear after the annealing and their relative concentration. The as-quenched sample spectra reveal the existence of two inequivalent sites for Fe. Such a feature is also observed in the remaining amorphous phase of the annealed samples. In the first steps of crystallization, α-Fe precipitates and its concentration increases with the annealing temperature. The experimental results suggest that the composition of the whole amorphous phase does not suffer large changes during crystallization. (orig.)

[en] The stress and annealing dependence of the Curie temperature in FeZrBCu alloys is presented. A change of about 50 /GPa has been observed. The change in amorphous matrix composition upon crystallization produces an expected increase in T_C (about 200 C) which is similar to the experimentally observed increase. This behaviour is opposite to that observed in Fe-Nb based alloys. (orig.)