Compositional Effect on Soft Magnetic Properties of Co-Fe-Si-B Amorphous Alloys with Zero Magnetostriction

The compositional effect on magnetic properties of Co-Fe-Si-B amorphous alloys was examined with the aim of finding an optimum composition for a magnetic head material. The lowest coercivity (H_c) and the highest permeability at 0.3 kHz (μ_0.3) in the as-quenched state were obtained at 0.94Co/(Co + Fe) and in the metalloid range of 24 to 25%(Si + B) and 0.6Si/(Si + B). The composition range is in agreement with that in which the highest glass-forming capacity is obtained and hence the good soft magnetic properties in the limited composition range are presumably due to a high degree of amorphicity and structural homogeneity. The permeability at 100 kHz (μ₁₀₀) shows a maximum value in the range of 27%(Si + B) and 0.65 to 0.70Si/(Si + B) and the difference of the optimum compositions between μ_0.3 and μ₁₀₀ is due to the necessity of high electrical resistivity for μ₁₀₀. The annealing results in the change of the optimum composition to 0.6Si/(Si + B) for μ₁₀₀ and 0.5Si/(Si + B) for H_c. The annealing-induced change is interpreted from the difference in the compositional effect on the homogeneity and thermal stability of the amorphous structure. Thus, the combination of high magnetization values of 98×l0^-6 to 113 × 10^-6 wb.m.kg^-1 and high permeability at 0.3 kHz reaching 19.21 × 10⁴ in the annealed state is achieved at 0.6Si/(Si + B) where the amorphous structure has high thermal stability and hence the metalloid composition is concluded to be optimum for an amorphous magnetic head material.