Magnetoimpedance effect in zero magnetostriction nanocrystalline Fe73.5Cu1Nb3Si16.5B6 ribbons

The field and frequency dependences of the impedance in Fe73.5Cu1Nb3Si16.5B6 ribbons are reported here. The samples were annealed for 1 h at temperatures between 400 and 630 degrees C leading to devitrification of the initial state into multiphase systems in order to study the correlation between the magnetoimpedance effect and the evolution of magnetostriction and structure with thermal treatments. The maximum magnetoimpedance ratio of around 30% is obtained after annealing in the range of temperatures 550-570 degrees C, where the samples show an optimum nanocrystalline state with grain size of around 12 nm and a softer magnetic behaviour. After annealing in that range of temperature, a change of magnetostriction sign from positive to negative is also observed. (C) 1998 Elsevier Science B.V. All rights reserved.