Nanocrystallization in Fe_73.5Si_13.5B ₉Mo₃Cu₁ amorphous ribbon and its magnetic properties

We present the magnetic characterization of nanocrystalline amorphous ribbons with nominal composition Fe_73.5B₉Si _13.5M_o3Cu₁, obtained by melt spinning. An annealing treatment was made on the alloys during 10, 20, 40, 50, 60 and 70 minutes at 400°C, in order to induce a nanocrystalline phase. Measurements of magnetization were made to evaluate the coercive field (H_C) as a function of annealing time. Results of vibrating sample magnetometry (VSM) show two important changes: a decrease in HC value as annealing time increases, until reaching a minimum value of 31 Oe, corresponding to the amorphous ribbon with annealing time of 20 minutes. This behavior indicates a soft magnetic state suggesting a structural relaxation. At this time, it is observed the best magnetic properties. In the second change, H_C increases until reaching a maximum value of 34 Oe, corresponding to 60 minutes. This increase indicates the onset of nanocrystallization state for the FeMo phase. In order to evaluate the magnetic anisotropy field (H_K), measurements of low field absorption (LFA) were carried up by means of an electronic paramagnetic resonance (EPR) spectrometer modified. The peak-to-peak linewidth (ΔH _PP-LFA) of LFA signal is associated with H_K, therefore H_K can be evaluated during the different annealing times.