Magnetoimpedance effect in amorphous and nanocrystalline alloys based on iron

Abstract

Purpose: The main purpose of the paper is to study magnetic, electrical and plastic properties of the selected group of amorphous alloys in the context of their application as magnetoimpedance sensors. Design/methodology/approach: The presented results were obtained by applying different magnetic methods (low field permeability measurements, magnetic relaxation, magnetization versus magnetic field, magnetization in saturation versus temperature, magnetoimpedance effect versus static magnetic field and/or frequency), resistivity versus temperature and Young’s modulus versus temperatures. Structural changes taking place in annealed samples were examined by making use of X-ray diffraction method and high resolution electron microscopy observations. Findings: It was shown that in all examined amorphous alloys soft magnetic properties can be enhanced by applying a suitable 1-h annealing at temperatures Top listed in Table 1. After annealing at this characteristic temperature magnetic permeability in relation to the as quenched state increases more than 20 times and non-contact magnetoimpedance effect (ΔZ/Z)ncmax is of the order of 104%. This effect can be explained based on the random anisotropy model supplemented by energy terms describing magnetoelastic energy and stabilization energy related to free volume content. For the alloys for which the optimized microstructure corresponds to the relaxed amorphous phase the plastic deformation corresponding to formation of brittle cracks is much higher than for the examined nanostructured alloys. In the frequency range from 700 kHz to 2 MHz magnetoimpedenace effect (ΔZ/Z)ncmax is approximately constant. Research limitations/implications: Searching of new soft magnetic materials in the group of amorphous alloys based on iron obtained by melt spinning can give a promising result. For example one can obtain very good soft magnets showing also good mechanical properties. Practical implications: Based on the presented results one can obtain very good soft magnetic material with low field relative magnetic permeability of about 16 000 (Fe74Cu1Zr3Si13B9). In the examined group of amorphous alloys the best candidate for magnetoimpedane sensor applications is the Fe75,75Ag0,25Nb2B22 alloy for which (ΔZ/Z)ncmax = 104% and plastic deformation εop=0.015. Silver as an alloying addition to the base Fe-Nb-B alloy significantly improves the alloy plasticity. Originality/value: It was shown that the examined amorphous alloys based on iron after applying a suitable thermal annealing can be used as promising materials for nagnetoimpedance sensors.