M.L. Sánchez

Giant magneto-impedance effect in nanostructured magnetic wires

The giant magneto‐impedance effect (GMI) is studied as a function of the structural modification induced in an Fe73.5Si13.5B9Cu1Nb3 amorphous alloy wire by annealing. The values of GMI are correlated to those structural changes and with the corresponding variation of the magnetic properties and intrinsic resistivity. Excellent soft magnetic properties, associated with low resistivity values, make this nanostructured material as one of the most promising for future applications of the GMI effect. The tailoring of the structure which can be induced by adequate thermal treatments easily allows one to obtain excellent combinations of circumferential permeability μφ and resistivity ρ during different devitrification stages, in order to produce materials for specific aims. Maximum GMI ratios of 200% are found after annealing the wires in the range 550–600 °C, where an optimum compromise between μφ and ρ is found. A simple model is developed correlating the fundamental physical properties of the soft magnetic wi...

Giant-magnetoimpedance-based sensitive element as a model for biosensors

We study the magnetoimpedance effect, using a Co67Fe4Mo1.5Si16.5B11 amorphous, ribbon-based sensitive element, in the presence of a commercial Ferrofluid® liquid thin layer covering the ribbon surface. The magnetoimpedance response is clearly dependent on the presence of the magnetic ferroliquid, the value of the applied magnetic field, and the parameters of the driving current. The magnetoimpedance-based prototype is proposed as a biosensor with high sensitivity to the fringe field produced by magnetic nanoparticles. A special advantage of this sensor is its high stability to chemical aggressive media; hence, it can be used for in situ measurements during fabrication of biomaterials with a high level of affinity and specificity with nanoparticles employed as bimolecular labels.

Giant magnetoimpedance effect in soft magnetic wires for sensor applications

Abstract The giant magneto-impedance effect (GMI) consists of the large relative change of the impedance (up to around 300%) observed in magnetically very soft ribbon and wire alloys under the application of dc magnetic fields (units of kA m 1 ). The phenomenology of the GMI effect is firstly described including a discussion about its origin which mainly lies in the classical skin-effect. An alternative approach to GMI phenomena considering equivalent circuits is also introduced. The main requirements to detect GMI is to count on a sample with very large circular susceptibility and reduced resistivity provided the frequency of the ac current flowing along the sample (necessary to evaluate the impedance) is high enough (roughly above 0.1 MHz for most samples here considered). The dependence on dc magnetic field, mechanical stresses and particularly on thermal treatments resulting in the induced magnetic anisotropies or in the devitrification of amorphous samples into a nanocrystalline structure are reviewed. First results on GMI in glass-coated amorphous microwires are also reported. The use of the GMI as a tool for studying the inner circular magnetization process or for evaluating the magnetostriction is introduced. Finally, a description on various aspects regarding the development of magnetic field, current, proximity and stress sensor applications is presented.

Martensitic phase transformation in rapidly solidified Mn50Ni40In10 alloy ribbons

Heusler alloy Mn50Ni40In10 was produced as preferentially textured ribbon flakes by melt spinning, finding the existence of martensitic-austenic transformation with both phases exhibiting ferromagnetic ordering. A microcrystalline three-layered microstructure of ordered columnar grains grown perpendicularly to ribbon plane was formed between two thin layers of smaller grains. The characteristic temperatures of the martensitic transformation were MS=213K, Mf=173K, AS=222K, and Af=243K. Austenite phase shows a cubic L21 structure (a=0.6013(3)nm at 298K and a Curie point of 311K), transforming into a modulated fourteen-layer modulation monoclinic martensite.

Magnetoimpedance effect in amorphous and nanocrystalline ribbons

The magnetoimpedance effect in several Co-rich amorphous ribbons is overviewed. Results are classified in the following sections: influence of anisotropies induced by stress annealing, dependence on applied stress, its dependence on stress or stress-impedance, and the appearance of hysteresis. The influence of nanocrystallization of given Fe-rich ribbons is also analyzed.

Correlation between structure, magnetic properties and MI effect during the nanocrystallisation process of FINEMET type alloys

FeNbCuSiB metallic glasses show excellent soft magnetic properties in nanocrystalline state such as high saturation induction and permeability, low magnetostriction, coercive field and anisotropy, which make these materials very suitable for use in magnetic devices or sensors based on magnetoimpedance (MI) effect. The main aim of this paper is to emphasise the great importance of structure characterisation when a complete understanding of the magnetic behaviour is pursued. In this way, we present an exhaustive study of the correlation between the magnetic properties and the structural changes occurring along the crystallisation process, focusing our interest on the first stages of the crystallisation, where magnetic parameters, such as the magnetic permeability or the Curie temperature of the amorphous matrix, together with magnetic domain structure undergo more sensitive changes. Several experimental results obtained by means of X-ray and neutron diffraction, differential thermal analysis, thermomagnetization, Mossbauer spectroscopy, hysteresis loops and MI measurements or surface domain structure observation are presented and discussed.

Magneto-impedance effect in nanostructured soft ferromagnetic alloys

Nanostructured Fe-based alloys have softer magnetic properties, such as larger saturation polarizations and magnetic permeabilities, smaller anisotropies and coercive fields and vanishing magnetostrictions, than their precursor alloys in the amorphous state. The softest magnetic properties are obtained for the smallest nanocrystalline grain sizes (between 10 and 20 nm), and these nanostructured materials are very suitable for use as high-frequency electronic components in magnetic devices or magnetic sensors based on the magnetoimpedance (MI) effect. In this work we study the correlation between the structural, electrical and magnetic properties together with the MI effect response in some heat-treated Finemet type and FeZrB ribbons. We show that the maximum MI ratio of around 130% and a sensitivity to the applied magnetic field of 0.07% (A m−1)−1 is obtained in the heat-treated samples that show an optimum nanocrystalline state and exhibit softer magnetic properties.

The torsional dependence of the magneto-impedance effect in current-annealed Co-rich amorphous wires

We report in this work the behaviour of the magneto-impedance in twisted wires of amorphous that have been subjected to a current annealing with an applied tensile stress and have various induced anisotropies and saturation magnetostriction coefficients. The samples were annealed at 0.5 A for 1 min, with applied stresses in the range 100-800 MPa. The magneto-impedance is studied in the best frequency and current-amplitude ranges. High sensitivities to the applied magnetic field (up to ) and to the torsion (around ) are obtained.

Influence of induced anisotropy on magneto-impedance in Co-rich metallic glasses

Abstract Large variations of magneto-impedance (MI) have been observed in amorphous ribbons (for drive frequencies higher than 100 kHz) subjected to a bias magnetic field of the order of a few Oe. The effect of induced anisotropies on the MI effect for Co 66.5 Fe 3.5 Si 12 B 18 ribbons is presented. Sensitivities to the applied bias field of 30 and 40%/Oe were obtained at 2 MHz.

FIELD AND FREQUENCY DEPENDENCE OF THE MAGNETO-IMPEDANCE IN CO-RICH AMORPHOUS RIBBON

Abstract In this paper we report measurements of the recently discovered magneto-impedance effect in as-quenched FeCoSiB ribbon possessing a low negative magnetostriction. The magneto-impedance shows a strong dependence on the drive current frequency and amplitude, and on the bias magnetic field. We have also studied the influence of the ribbon length on this effect. We obtained a sensitivity to the applied bias field of 13%/Oe at 2 MHz. This phenomenon points out the enormous potential of this material for technological applications such as sensitive magnetic heads and magnetic field sensors. The results can be explained by changes in the transverse magnetization due to the drive current and the field dependence of the skin depth through the transverse permeability.