Structural and magnetic properties of the nanocrystalline alloy Fe₈₆Zr₇Cu₁B₆

A detailed study on the nanocrystallization and its correlation with the attractive soft magnetic properties of the alloy Fe₈₆Zr₇Cu₁B₆ (at %) is presented. Melt-spun amorphous ribbons were submitted to Joule heating for a short time interval (t_a=50 s) with different direct current values. The electrical resistance measured during heating showed strong variations associated with the nucleation and growth of α-Fe nanocrystals. From x-ray diffraction line profile analysis we obtained the average grain size, crystalline volume fraction, grain size distribution function, and lattice distortions for different annealing currents. The results display an excellent agreement with the magnetic characterization (ac initial permeability and dc hysteresis loops), showing that the optimum soft magnetic behavior is associated with the formation of about 50% in volume of the α-Fe nanophase. The extended x-ray absorption fine structure (EXAFS) technique was applied to study the evolution of the short-range ordering around Fe atoms. EXAFS spectra also showed the evolution from a disordered Fe environment to the bcc crystalline arrangement. The onset of crystallization determined from both techniques is slightly different, indicating that the nanocrystallization begins at the surface of the studied samples. © 1999 American Institute of Physics.