Investigation on the Giant Magnetoimpedance of Fe<SUB>89−<I>x</I></SUB>Zr<SUB>7</SUB>B<SUB>4</SUB>Al<I><SUB>x</SUB></I> (<I>x</I>=0 and 2.5) Nanocrystalline Ribbons

Abstract

In the present work, annealing effects upon the crystallization and giant magnetoimpedance (GMI) of Fe86.5Zr7B4Al2.5 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 Fe86.5Zr7B4Al2.5, 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 Fe86.5Zr7B4Al2.5. 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).