G. Vara

Influence of corrosion on surface magnetic density in amorphous and nanocrystalline Fe73.5Cu1Nb3Si13.5B9 alloys

The variation of surface magnetization with corrosion in Fe73.5Cu1Nb3Si13.5B9 in the amorphous and nanocrystalline states is investigated. The results show that in the amorphous samples when the oxidized layer increases the surface saturation magnetization decreases. However, in the nanocrystalline samples the surface saturation magnetization does not change significantly with the corrosion process but the approximation to saturation is different in the non-oxidized and oxidized nanocrystalline samples. In the case of non-oxidized samples, the surface saturation magnetization is reached at a low applied magnetic field (1000 Am−1), whereas in the oxidized samples it is reached at a higher applied magnetic field of 7000 and 9000 Am−1 for the samples annealed at 520°C for 60 min and 30 min, respectively.

Nanocrystallization by current annealing (with and without tensile stress) of Fe73.5-xNixSi13-5B9Nb3Cu1 alloy ribbons (x=5, 10, and 20)

Microstructural (crystalline volume fraction and grain size), magnetization (coercive field), and saturation magnetostriction measurements in Fe73.5−xNixSi13.5B9Nb3Cu1 alloy ribbons (x=5, 10, and 20) treated by current annealing and stress-current annealing are presented. Microstructural analysis of the treated ribbons using x-ray diffraction showed a high content of the amorphous phase in the bulk. In addition, substantial changes in the crystalline state such as grain size of the samples annealed at different conditions were observed. The alloy composition also affects greatly the grain size: increase in Ni content leads to higher values of the average grain size. The evolutions of the coercive field with the two kinds of thermal treatment were analyzed, allowing us to conclude that the addition of Ni tends to reduce the magnetic softness of the original material and that the coercivities are higher in the samples treated by stress annealing than in those treated without tensile stress. On the other han...