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Magnetoimpedance effect in amorphous and nanocrystalline alloys based on iron

Kwapuliński P.

Journal of Achievements in Materials and Manufacturing Engineering

2011

Vol. 47, nr 2

166--176

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 noncontact 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.

High frequency magneto-impedance effect in glass-coated amorphous Co83.2 B3.3 Si5.9 Mn7.6 microwires

Lee H., Kim Y. S., Yu S. C.

Materials Science

2003

Vol. 21, No. 1

115-121

The measurements of the giant magneto-impedance (GMI) were carried out in the amorphous Co83.2B3.3Si5.9Mn7.6 micro-wires at high frequency range from 100 MHz up to 1 GHz of an accurrent flowing along the wire and at varying axial dc-magnetic field in its range of š120 Oe. The wires, about 15žm in diameter, were fabricated by a glass-coated melt spinning technique. The shape of the impedance curves plotted vs. a dc-field is changing dramatically with the frequency. The phase angle was also strongly dependent on this field. The maximum value of GMI, around 250%, was reached at the frequency of about 500 MHz. The external dc-magnetic field changes the circumferential permeability as well as the penetration depth, both in turn change the impedance of the sample. The increments of GMI at high frequency can be understood in terms of the LC- resonance phenomena. The sudden change of the phase angle, as large as 180°, evidenced the occurrence of the resonance at a given intensity of the external dc-field.