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MnCoSi and MnCoSiB0.5 alloys were obtained by melt-spinning technique in order to attain polycrystalline microstructures with average grain sizes well below 10 microns. Phase distribution studied by X-ray analysis indicated single-phase materials with orthorhombic structure and TiNiSi-type crystal symmetry. Chemical homogeneity was verified by means of scanning electron microscopy, whereas magnetic behavior corresponded to soft magnetic materials with coercivity values lower than 20 Oe and saturation magnetization of 80 emu/g. Magnetocaloric response of these MnCoSiB alloys was characterized by a maximum magnetic entropy change of 1.0 J/kg K (for a magnetic field variation of 2.0 Tesla) and attractive refrigerant capacity over 100 J/kg, which represents a significant enhancement respect to equivalent MnCoGe alloys. [ABSTRACT FROM AUTHOR]

A systematic study of die-cast REFeAl (RE = Nd + Pr) bulk amorphous alloys with small B, Cu, and Dy additions is presented. Differential scanning calorimetry and x-ray diffraction data are consistent with an amorphous microstructure and a small amount of hcp Nd-type crystallites embedded in the amorphous matrix for B, Cu+ B-, and Dy-containing alloys. Coercivity, H[SUBc], exhibits a progressive enhancement upon B, B+ Cu, and Dy addition (from 284 kA/m for Nd[SUB30]Fe[SUB60]Al[SUB10] up to 388 kA/m for Dy substituted alloy). This H[SUBc] improvement is associated not only with domain wall pinning on the crystallites, but also with the increase of nucleation sites and thus, with the number of RE and RE-Fe-Al clusters. In agreement with the latter, a superparamagnetic behavior, which is characteristic of a clustered structure, was observed above 451 K for all the alloy compositions. [ABSTRACT FROM AUTHOR]

Abstract: In the present research work, thermal stability, magnetic properties and microhardness of Fe72B19.2Si4.8M4 (M=Ta or Y) amorphous ribbons obtained by chill block melt-spinning technique are reported. The crystallization temperatures resulted as high as 1129K (for M=Ta) and of 1167K (for M=Y), which indicate a considerable thermal stability for both alloys. On the other hand, the saturation polarization (μ 0 M s) together with the Curie temperature (T c) also showed excellent combination of values, with 0.95±0.12T and 586±8K, respectively (for the Ta-containing alloy) and of 1.55±0.18T and 698±6K, respectively (for the Y-containing alloy). Additionally, the Vickers microhardness exhibited values over 1100kg/mm2 for both alloys. [Copyright &y& Elsevier]

Abstract: Considerable enhancement of magnetic properties was attained in initially stoichiometric nanophase RE12Fe82B6 melt-spun alloys (RE=Nd, Nd+Pr) by means of an excess B content (10at%) and additions of Zr and Co (2% and 7%, respectively). The intrinsic coercivity exhibited a marked improvement (with respect to the stoichiometric 6at% B alloy), within the range 50–65%, with a maximum of 1161±14kAm−1 for the B-rich and Zr-containing alloy, together with an excellent combination of remanence and energy density values of 0.90±0.01 T and 137±4kJm−3, respectively. Further Co addition led to a Curie temperature increase, while preserving high coercivity (1176±31kAm−1) and useful energy densities (119±4kJm−3). Results were interpreted on the basis of alloy microstructural features and on variations of the intrinsic magnetic properties, supported by micromagnetic calculations. [Copyright &y& Elsevier]

Abstract: We report and discuss the results of a study of the structures and magnetic properties of B-rich (10at%) nanocomposite alloys, based on the formula (Nd0.75Pr0.25) y (Fe0.9Co0.1)90− y − x NbxB10 (, 10; , 2,4) and processed by devitrification of melt-spun amorphous precursors. Considerable enhancement of the intrinsic coercivity, together with good to excellent remanence and energy density values were observed for the composition with , , (1042kA/m, 0.88T and 123kJ/m3, respectively). The intrinsic coercivity and remanence enhancements are ascribed to the grain-refining effects of Nb, particularly with respect to the soft-magnetic phases, and thus to more complete exchange coupling of the soft grains to the hard-phase grains than for the Nb-free alloy. [Copyright &y& Elsevier]

The effect of Cr substitution for Fe on the mechanical properties of Fe78−xCrxSi10B12 and Fe77.5−xCrxSi7.5B15 (0⩽x⩽8) melt spun alloy series is presented. The tensile strength of the as-cast ribbons increased slightly with the substitution of Fe by Cr from 1.5 GPa (x=0) to 2.5 GPa (x=8) for Fe78−xCrxSi10B12 alloys, and from 2.2 GPa (x=0) to 2.9 GPa (x=8) for Fe77.5−x CrxSi7.5B15 alloys. The Vickers microhardness remained almost constant for all Cr contents. In addition, the effect of annealing (30 min at various temperatures) on both, the tensile stress and microhardness of Fe70Cr8Si10B12 alloy was also determined. A gradual decrease with increasing annealing temperature was observed at the former and an increasing trend with higher anneal temperatures for the latter. Results are explained in terms of enhanced bond interaction metal–metalloid and of structural relaxation after heat treatment. [Copyright &y& Elsevier]

Abstract: In this report, we study the effect of Cr addition on the dc an ac magnetic properties of novel melt spun amorphous Co43−x/2Fe20−x/2Cr x B31.5Ta5.5 (x =0,1,2,4) alloy series. The saturation magnetization decreases with increasing Cr content as well as the ac relative initial permeability, which showed a high relaxation frequency of 3MHz. In addition, the magnetoimpedance effect was detected in this alloy series, with a maximum variation ratio of 3% at x =0. [Copyright &y& Elsevier]

The structures and magnetic properties of melt-spun B-rich (10 at. %) and Nb-containing nanocomposite alloys, with compositions based on the formula (Nd0.75Pr0.25)yFe90-y-xNbxB10 (y=8, 10; x=0, 2, 4) have been studied. Considerable enhancement of the intrinsic coercivity, (of 657 kA/m) together with excellent energy density (of 113 kJ/m3), were observed for y=8, x=4; while for y=10 and x=2, values of 912 kA/m and 140 kJ/m3 were attained. Results are interpreted in terms of a grain size refining effect of the Nb addition and to the more complete exchange coupling of the soft grains to the hard phase grains afforded by reduced grain sizes. [ABSTRACT FROM AUTHOR]

Abstract: Ferromagnetic resonance (FMR) measurements were carried out on soft magnetic amorphous ribbons of composition Co66Fe4B12Si13Nb4Cu prepared by melt spinning. In the as-cast sample, a simple FMR spectrum was apparent. For treatment times of 5–20min a complex resonant absorption at lower fields was detected; deconvolution calculations were carried out on the FMR spectra and it was possible to separate two contributions. These results can be interpreted as the combination of two different magnetic phases, corresponding to the amorphous matrix and nanocrystallites. The parameters of resonant absorptions can be associated with the evolution of nanocrystallization during the annealing. [Copyright &y& Elsevier]