Electronic Surveillance and Security Applications of Magnetic Microwires

Applications in security and electronic surveillance require a combination of excellent magnetic softness with good mechanical and anticorrosive properties and low dimensionality. We overviewed the feasibility of using glass-coated microwires for electronic article surveillance and security applications, as well as different routes of tuning the magnetic properties of individual microwires or microwire arrays, making them quite attractive for electronic article surveillance and security applications. We provide the routes for tuning the hysteresis loops’ nonlinearity by the magnetostatic interaction between the microwires in the arrays of different types of amorphous microwires. The presence of neighboring microwire (either Fe- or Co-based) significantly affects the hysteresis loop of the whole microwires array. In a microwires array containing magnetically bistable microwires, we observed splitting of the initially rectangular hysteresis loop with a number of Barkhausen jumps correlated with the number of magnetically bistable microwires. Essentially, nonlinear and irregular hysteresis loops have been observed in mixed arrays containing Fe- and Co-rich microwires. The obtained nonlinearity in hysteresis loops allowed to increase the harmonics and tune their magnetic field dependencies. On the other hand, several routes allowing to tune the switching field by either postprocessing or modifying the magnetoelastic anisotropy have been reviewed. Nonlinear hysteresis loops have been also observed upon devitrification of amorphous microwires. Semihard magnetic microwires have been obtained by annealing of Fe–Pt–Si microwires. The observed unique combination of magnetic properties together with thin dimensions and excellent mechanical and anticorrosive properties provide excellent perspectives for the use of glass-coated microwires for security and electronic surveillance applications.This work was funded by Spanish MCIU under PGC2018-099530-B-C31 (MCIU/AEI/FEDER, UE) by the Government of the Basque Country under PIBA 2018-44 project and Elkartek (CEMAP and AVANSITE) projects and by the University of Basque Country under the scheme of “Ayuda a Grupos Consolidados” (Ref.: GIU18/192)

Magnetic microwires with unique combination of magnetic properties suitable for various magnetic sensor applications

There is a pressing demand to improve the performance of cost-effective soft magnetic materials for use in high performance sensors and devices. Giant Magneto-impedance effect (GMI), or fast single domain wall (DW) propagation can be observed in properly processed magnetic microwires. In this paper we have identified the routes to obtain microwires with unique combination of magnetic properties allowing observation of fast and single DW propagation and GMI effect in the same microwire. By modifying the annealing conditions, we have found the appropriate regimes allowing achievement of the highest GMI ratio and the fastest DW dynamics. The observed experimental results are discussed considering the radial distribution of magnetic anisotropy and the correlation of GMI effect, and DW dynamics with bulk and surface magnetization processes. Studies of both Fe- and Co-rich microwires, using the magneto-optical Kerr effect, MOKE, provide information on the magnetic structure in the outer shell of microwires. We have demonstrated the existence of the spiral helical structure in both studied microwires. At the same time, torsion mechanical stresses induce helical bistability in the same microwires, which allow us to consider these microwires as materials suitable for sensors based on the large Barkhausen jump.This work was funded by Spanish MCIU under PGC2018-099530-B-C31 (MCIU/AEI/FEDER, UE) by the Government of the Basque Country under PIBA 2018-44 project and Elkartek (CEMAP and AVANSITE) projects and by the University of Basque Country under the scheme of “Ayuda a Grupos Consolidados” (Ref.: GIU18/192)

Post-processing Routes for Design of Giant Magnetoimpedance Response and Domain Wall Dynamics Control in Glass-coated Magnetic Microwires

215 p.En esta tesis se presenta el estado actual del arte en la producción, propiedades y aplicaciones demicrohilos magnéticos recubiertos de vidrio junto con las técnicas experimentales empleadas para laproducción y caracterización de los materiales estudiados se tratan efectos novedosos en microhilosmagnéticamente blandos recubiertos de vidrio. El trabajo se enfoca en: i) microhilos amorfos ricos en Fecon tratamiento térmico optimizado para la mejora del efecto de magnetoimpedancia gigante (GMI) ydinámica de pared de dominio mejorada; ii) microhilos amorfos a base de Fe y Co con anisotropíamagnética graduada; y iii) Microhilos basados en Co con efecto conjunto de alto GMI y rápidapropagación de pared de dominio único. La última sección está dedicada a la nueva posibilidad deaplicación de microhilos recubiertos de vidrio en compuestos inteligentes con microhilos integrados

Correlation of crystalline structure with magnetic and transport properties of glass-coated microwires

We overviewed the correlation between the structure, magnetic and transport properties of magnetic microwires prepared by the Taylor-Ulitovsky method involving rapid quenching from the melt and drawing of the composite (metallic core, glass coated) wire. We showed that this method can be useful for the preparation of different families of magnetic microwires: soft magnetic microwires displaying Giant magnetoimpedance (GMI) effect, semi-hard magnetic microwires, microwires with granular structure exhibiting Giant Magnetoresistance (GMR) effect and Heusler-type microwires. Magnetic and transport properties of magnetic microwires depend on the chemical composition of metallic nucleus and on the structural features (grain size, precipitating phases) of prepared microwires. In all families of crystalline microwires, their structure, magnetic and transport properties are affected by internal stresses induced by the glass coating, depending on the quenching rate. Therefore, properties of glass-coated microwires are considerably different from conventional bulk crystalline alloys.This work was supported by Spanish Ministry of Economy and Competitiveness (MINECO) under Projects MAT2013-47231-C2-1-P and MAT2013-47231-C2-2-P. The authors thank for technical and human support provided by SGIker (Magnetic Measurements Gipuzkoa) of UPV/EHU. VZ and AZ wish to acknowledge the support under Program of Mobility of the Researchers of the Basque Government (grants MV-2016-1-0025 and MV-2016-1-0018 respectively)

Review of domain wall dynamics engineering in magnetic microwires

The influence of magnetic anisotropy, post-processing conditions, and defects on the domain wall (DW) dynamics of amorphous and nanocrystalline Fe-, Ni-, and Co-rich microwires with spontaneous and annealing-induced magnetic bistability has been thoroughly analyzed, with an emphasis placed on the influence of magnetoelastic, induced and magnetocrystalline anisotropies. Minimizing magnetoelastic anisotropy, either by the selection of a chemical composition with a low magnetostriction coefficient or by heat treatment, is an appropriate route for DW dynamics optimization in magnetic microwires. Stress-annealing allows further improvement of DW velocity and hence is a promising method for optimization of DW dynamics in magnetic microwires. The origin of current-driven DW propagation in annealing-induced magnetic bistability is attributed to magnetostatic interaction of outer domain shell with transverse magnetization orientation and inner axially magnetized core. The beneficial influence of the stress-annealing on DW dynamics has been explained considering that it allows increasing of the volume of outer domain shell with transverse magnetization orientation at the expense of decreasing the radius of inner axially magnetized core. Such transverse magnetic anisotropy can similarly a ect the DW dynamics as the applied transverse magnetic field and hence is beneficial for DW dynamics optimization. Stress-annealing allows designing the magnetic anisotropy distribution more favorable for the DW dynamics improvement. Results on DW dynamics in various families of nanocrystalline microwires are provided. The role of saturation magnetization on DW mobility improvement is discussed. The DW shape, its correlation with the magnetic anisotropy constant and the microwire diameter, as well as manipulation of the DW shape by induced magnetic anisotropy are discussed. The engineering of DW propagation through local stress-annealing and DW collision is demonstrated.This research was funded by Spanish MCIU under PGC2018-099530-B-C31 (MCIU/AEI/FEDER, UE), by the Government of the Basque Country under PIBA 2018-44 and Elkartek (CEMAP and AVANSITE) projects, and by the University of Basque Country under the scheme of “Ayuda a Grupos Consolidados” (Ref.: GIU18/192). J.O. wishes to acknowledge the support of the Ministry of Higher Education, Science and Technology of the Dominican Republic (2015 FONDOCyT program)

Reversible and Non-Reversible Transformation of Magnetic Structure in Amorphous Microwires

We provide an overview of the tools directed to reversible and irreversible transformations of the magnetic structure of glass-covered microwires. The irreversible tools are the selection of the chemical composition, geometric ratio, and the stress-annealing. For reversible tuning we use the combination of magnetic fields and mechanical stresses. The studies were focused on the giant magnetoimpedance effect and the velocity of the domain walls propagation important for the technological applications. The essential increase of the giant magnetoimpedance effect and the control of the domain wall velocity were achieved as a result of the use of two types of control tools. The performed simulations reflect the real transformation of the helical domain structures experimentally found.This research was funded by National Science Centre Poland under Grant No. DEC-2016/22/M/ST3/00471, Spanish MCIU under PGC2018-099530-BC31 (MCIU/AEI/FEDER, UE), the Government of the Basque Country under PIBA 2018-44 projects. The authors thank for technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF). The research of P.G. was supported in part by PL-Grid Infrastructure

Novel Magnetic Properties in Curved Geometries

This reprint focuses on fundamentals and applied research on magnetic structures with curved geometries. The influence of curvature in the magnetic structures is an appealing topic of research opening novel perspectives to engineer the magnetic textures and the magnetisation reversal processes. Special attention is given to the fabrication and optimisation of magnetic structures, their characterisation and possible use in technological applications

Optimization of magnetic composites properties for low and high frequency applications by advanced mechanical alloying techniques of amorphus materials

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de Materiales, leída el 07-03-2017La presente tesis doctoral se centra en el desarrollo de materiales magnéticos como son las ferritas y los materiales magnéticamente blandos amorfos y nanocristalinos, en forma de cintas y microhilos. La estructura y propiedades magnéticas de estos materiales han sido optimizadas mediante el empleo de diferentes técnicas de molienda mecánica. Esto ha permitido la fabricación de materiales compuestos para aplicaciones de apantallamiento electromagnético e imanes permanentes isótropos libres de tierras raras. Las aleaciones nanocristalinas basadas en Fe y FeCo son bien conocidas por presentar unas adecuadas propiedades magnéticas como material blando, que las hacen adecuadas para aplicaciones específicas. En este trabajo, se han utilizado diferentes técnicas de molienda mecánica de bolas de alta energía (en medio seco y húmedo) y criomolienda, para obtener polvo de tamaño submicrométrico de cintas nanocristalinas y microhilos amorfos. Se ha estudiado la influencia de las técnicas de molienda seleccionadas sobre la microestructura y las propiedades magnéticas blandas del producto final. Se han empleado microhilos amorfos para fabricar materiales compuestos de matriz polimérica destinados a aplicaciones de atenuación de microondas, cuyas propiedades dependen de la relación de aspecto y longitud final de los microcrohilos. Así mismo, se han caracterizado a alta frecuencia láminas de material compuesto con diferentes espesores y con un contenido variable de polvo de microhilo y de microhilos de 2 mm de longitud, considerando además la naturaleza conductora o no conductora de la matriz. Así, se han obtenido valores de atenuación y de ancho de banda superiores a los que presentan otros tipos de materiales compuestos de matriz polimérica reforzados con microhilos. Los datos experimentales obtenidos se han validado mediante el empleo de la aproximación de medio efectivo de Maxwell Garnett. Por otro lado, la creciente demanda de imanes permanentes ha impulsado la investigación para reducir el uso de tierras raras en su proceso de fabricación. En este trabajo, se han combinado ferritas de Sr tipo M como fase dura con polvo nanocristalino de Fe y FeCo como fase blanda, con objeto de alcanzar un acoplamiento efectivo entre las fases que permita obtener un elevado producto máximo de energía. Así pues, se ha desarrollado un procedimiento de molienda mecánica de bolas de alta energía para obtener una dispersión homogénea de ambas fases y preservar las propiedades estructurales de las fases individuales. De este modo, se ha conseguido obtener un material compuesto que presenta un producto máximo de energía superior en un 30% al que presentan las ferritas comerciales y cuyo proceso de obtención presenta adecuadas características para ser industrializado. Así mismo, se han realizado medidas de retroceso de histéresis, de imanación IRM y de desimanación DC, así como curvas Henkel para analizar la naturaleza de las interacciones magnéticas entre las fases duras y blandas. Por otro lado, el comportamiento del material como una sola fase ha sido observado a partir de ciclos de histéresis medidos a 5 K, sin embargo, el análisis de la distribución de los campos de inversión ha mostrado procesos de desimanación independientes para dichas fases...Depto. de Física de MaterialesFac. de Ciencias FísicasTRUEunpu