Investigation on the Giant Magnetoimpedance of Fe_89−xZr₇B₄Al_x (x=0 and 2.5) Nanocrystalline Ribbons

Abstract

In the present work, annealing effects upon the crystallization and giant magnetoimpedance (GMI) of Fe_86.5Zr₇B₄Al_2.5 ribbons were investigated, in comparison with the case of Fe₈₉Zr₇B₄ ribbons. Annealing at 720°C for Fe₈₉Zr₇B₄ results in the formation of mixture of α-Fe and Fe₃Zr, and the appropriate addition of Al can restrain the Fe₃Zr precipitation. The optimum annealing temperature for obtaining the largest magnetoimpedance is 650°C for Fe₈₉Zr₇B₄, and is 720°C for Fe_86.5Zr₇B₄Al_2.5, where the permeability reaches its maximum value. The GMI effect depends not only on the permeability change with field, but also on the magnitude of the permeability itself. The reduction of the permeability and GMI at high annealing temperature is due to the occurrence of Fe₃Zr precipitation and the coarsening of α-Fe grains. The maximum magnetoimpedance (ΔZ⁄Z₀)_max under applied magnetic field H=7162 A/m can reach −43.3% for Fe₈₉Zr₇B₄, and −45.8% for Fe_86.5Zr₇B₄Al_2.5. The appropriate Al addition in Fe-Zr-B ribbon not only lowers the transverse anisotropy, but also improves the change slope of impedance at low fields (H<1000 A/m).