Characterization and Analysis of Nanocrystalline Soft Magnetic Alloys: Fe Based

Soft magnetic nanocrystalline alloys have been widely analysed and studied during the past years. However, optimisation of specific chemical compositions is still being developed. The applicability of these soft nanocrystalline alloys depends mainly on the presence of the desired nanocrystalline phases within the alloy. In this study, the analysed alloys are manufactured by mechanical alloying. The analyses performed on the samples include a microstructural analysis, a thermal analysis, and a complementary functional analysis in the form of the thermomagnetic response of some samples. Regarding Fe-based alloys, thermal stability for samples containing B was higher than those containing P (crystal growth peaks in the range between 895–905 K and 775–800 K respectively). The higher magnetization of saturation, Ms, was found in Fe–Mn alloys, whereas the addition of boron provoked a decrease of Ms and the nanocrystals size.

Magnetic Properties in Finemet-Type Soft Magnetic Toroidal Cores Annealed under Radial Stresses

Applying tensile stresses on straight soft magnetic ribbons before core fabrication is a routine method of inducing magnetic anisotropy, while methods of stress annealing of ribbons after core winding are seldom explored. In this study, we utilize a novel approach to induce magnetic anisotropy by applying radial stresses on tape-wound cores of Fe73.5Si13.5B9Cu3Nb1 (at. %) ribbon during crystallization heat treatment. The results show that while stress annealing does not change the structural characteristics of annealed samples, the magnetic anisotropies induced can increase to values ~3–5 times larger than the sample annealed in the absence of external stress. This increase in magnetic anisotropy energy is associated with ~25–50% decrease of magnetic inductance in the treated cores. These results suggest that the magnetic properties of nanocrystalline soft magnetic alloys can be effectively tuned by applying radial stresses.

Thermal Stability of Nanocrystalline Soft Magnetic Alloys with Different Inhibitors

In this work, the effect of different inhibitors on the thermal stability of the magnetic properties in Fe73.5Cu1M3Si13.5B9 nanocrystalline alloys, where M = Nb, W, Mo, was investigated. Nanocrystalline alloy with tungsten has the greatest thermal stability. The change in the magnetic properties in the ageing process was associated with vacancies and vacancy clusters, the formation of which is facilitated by large atoms of inhibitory elements occupying free positions in the substitution solid solution.