The crystallization kinetics of amorphous Co_78-xFe _xSi₈B₁₄ ribbons

We have studied the crystallization kinetics of amorphous Co _78-xFe_xSi₈B₁₄ ribbons (x = 5, 10, 20, 30, 40, at.%) by using the resistivity monitoring method in the higher temperature region and also by using the method of differential thermal analysis (DTA). From 300 K to 1000 K, the φ-T curves of the amorphous alloys with different x are all of the same shape with dφ/dT≳0 before the crystallization starts and an abrupt drop, Δφ, during the crystallization process. The crystallization temperature T_cr lies between 750 K and 830 K and Δφ lies between 29 and 34 μΩ-cm. Experiments also show that after crystallization, the coercive force of these alloys increases conspicuously, some as high as 100-200 Oe. The DTA curves have two prominent exothermic peaks between 720-830 K. During the crystallization process, the curves display two distinct stages, showing that there are two crystallographic phases precipitated. In the vicinity of the temperature of crystallization, we also measured the isothermal variation of resistivity with time of the ribbon Co₅₈Fe₂₀Si₈B₁₄. From the annealing curves and Arrhenius relation, the activation energy was estimated to be 80 kcal/mole.