Effect of the annealing conditions and grain size on the soft magnetic character of FeCu(Nb/Ta)SiB nanocrystalline alloys

Melt spun amorphous Fe_73.5Si_13.5B₉Cu₁(Ta/Nb)₃ ribbons have been submitted to thermal treatments carried out both in a conventional furnace and by using the Joule heating technique. These treatments resulted in a partial devitrification to a nanocrystalline structure of the samples. The effect of the treatment parameters both on the magnetization work, W, and on the coercive force, H_c has also been investigated. Our conclusions correlate the dependence of W on the annealing parameters with the occurrence of structural relaxation in the amorphous phase and of domain wall pinning at the precipitated nanocrystals. In addition, the obtained coercive force dependence on the average grain size, D is discussed in the framework of an extended random anisotropy model. Discrepancies with the theoretical H_c∝D⁶ law were found which could be assigned to the role of inhomogeneous magnetic anisotropy induced by the Joule heating on the averaged magneto-crystalline anisotropy.