Improved magnetoimpedance and mechanical properties on nanocrystallization of amorphous Fe68.5Si18.5Cu1Nb3B9 ribbons

The effect of heat-treatment temperature on evolution of microstructures, mechanical and soft magnetic properties and magnetoimpedance (MI) effect in rapidly solidified Fe68.5Si18.5Cu1Nb3B9 ribbons, has been investigated. The as-quenched ribbons were subjected to heat-treatment at different temperatures between 400 and 600 °C for 1 h under high vacuum. Detailed structural studies on the ribbons heat-treated at and above 525 °C revealed the presence of nanocrystalline Fe3Si phases embedded in a residual amorphous matrix. The ribbon heat-treated at 550 °C temperature exhibits maximum ductility, maximum relative permeability of 4.8×104, minimum coercivity of 0.1 Oe, and maximum MI value of 62%. The enhanced MI effect is believed to be related to the magnetic softening of 550 °C heat-treated ribbons. However, the magnetic properties and MI effect deteriorated in the samples heat-treated above 550 °C due to the coarsening of grain sizes. The soft magnetic behavior of the nanocrystalline ribbons are discussed in the light of random anisotropy model, whereas the MI effect is discussed through standard skin effect in electrodynamics.