The influence of ultra-rapid annealing on nanocrystallization and magnetic properties of Fe_76−xNi₁₀B₁₄Cu_x alloys

Soft magnetic materials with a nanocrystalline structure are significant from an application and scientific point of view. This article presents the possibility of obtaining nanocrystalline Fe_76−xNi₁₀B₁₄Cu_x alloy with magnetic properties modified by ultra-rapid annealing (URA). The work is focused on thermodynamic calculations to determine the alloy's optimal copper content and achieving soft magnetic properties of selected material by ultra-rapid annealing. The examined copper concentration was in the range from 0 to 2 at%. The optimal copper concentration was investigated based on the minimization of the Gibbs free energy of amorphization value. Accordingly, the Fe_75.3Ni₁₀B₁₄Cu_0.7 alloy was taken for further experimental analysis. The URA process was performed in a specially designed, home-made apparatus, in which the amorphous precursor in the ribbon shape was annealed between hot blocks at 773 K for the time in the range of 0.5–30 s. The ribbons were examined in detail by differential scanning calorimetry, X-ray diffraction, and⁵⁷Fe Mössbauer spectroscopy. The nucleation mechanisms in the amorphous material upon crystallization have been studied. The dependence of the mean grain size and the content of the crystalline phase on annealing time was determined. The coercivity, H_c, and saturation magnetic polarization, J_s, measurements revealed changes in the alloy's magnetic behavior with increasing the annealing time. Optimal conditions of the URA process were determined in order to obtain soft magnetic Fe_75.3Ni₁₀B₁₄Cu_0.7nanocrystalline alloy.