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The recent work is focused on the development of suitable amorphous ferromagnetic microwires (CoFe-based) for use in giant magneto-impedance (GMI) magnetic sensing cores. Rapid solidification route is used for the preparation of microwires via in-rotating water quenching technique. The potential of the CoFeSiBCr soft magnetic microwires for GMI based sensing core is investigated by using the driving frequency of MHz range. The GMI characteristics of the developed materials are carried out via impedance-mode. The performance of the magnetic sensor is studied based on its maximum GMI ratio, magnetic field sensitivity and noise spectrum. The experimental results reveal that the maximum GMI ratio, GMImax of about 650% and field sensitivity of around 802 V/T is achieved at ac driving frequency of 5 MHz with 3 mA driving current when annealed at 750 K for 5 min. The noise level of the optimized microwire can be obtained under 10 nT/√Hz@1 Hz while driven at 5 MHz. By means of its high operating frequency regime, high sensitivity, low noise level and simple methodology for sensing, the GMI microwires working in impedance-mode can be a potential candidate for commercial sensing applications such as microfluxgate sensors.

International audience; Five adsorbents based on fly ash treated with NaOH for the adsorption of cadmium ion from aqueous solutions were investigated. The materials were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and the Brunauer-Emmett-Teller (BET) surface area methods. The results demonstrated that the specific surface area of fly ash was improved after NaOH treatment, and that the adsorption of cadmium by the new adsorbents reached equilibrium in less than 120 min. The results also confirmed that the materials treated with NaOH solution by direct activation had a higher adsorption capacity than untreated fly ash. The maximum adsorption capacities obtained were in the range of 9.18–48.5 mg/g. Also, SEM/EDS and FT-IR results of Cd(II) loaded adsorbents were performed. The obtained experimental data were used for kinetics determination using three model equations: a pseudo first-order model, a pseudo second-order model, and the intraparticle diffusion model. Was found that the adsorption of cadmium ions onto the adsorbents studied follows the pseudo second-order model. The adsorption isotherms of the adsorbent synthesized by direct activation for 15 h using 5 M NaOH at 90 °C with a ratio of 1:3 fly ash: NaOH (A5) was assessed in terms of the Langmuir (four types of linearization), Freundlich, Temkin, Harkin-Jura, and Halsey models. The effectiveness of the adsorbents was evaluated using the toxicity characteristic leaching (TCLP) procedure. Accordingly, the proposed methods in this study are recommended for advanced capitalization of fly ash, particularly as a potential adsorbent for the removal of cadmium ions from wastewater.

The use of materials at nanoscale is currently of increasing interest for life sciences and medicine. Magnetic nanoparticles (MNPs) are under scrutiny for a large array of applications in nanomedicine as diagnostic and therapeutic tools. Proprietary Fe-Cr-Nb-B MNPs display heating properties that recommends them as potent agents for delivery of local hyperthermia for the treatment of solid tumours. Stem cell mediated delivery represents a safe and accurate modality to target remote or metastatic tumour sites. In this study we investigated the interaction of Fe-Cr-Nb-B nanoparticles with human adipose derived mesenchymal stem cells and human primary osteoblasts. We found that: (a) bare and chitosan coated Fe-Cr-Nb-B are internalized by both cell types, (b) they can be detected up to 28 days inside the cells without signs of membrane disruption and (c) they do not display in vitro toxicity. MNPs are uploaded by cells in a time dependent manner with maximum uptake after 7-8 days cell-particle incubation. Particle internalization do not interfere with proliferative and differentiation potential (osteogenesis and adipogenesis) demonstrating an unaltered cellular phenotype. Further investigation of the potential effect of MNPs internalization on cytoskeleton dynamics and in inducing oxidative stress will be required as it is of interest for predicting cell migration and survival after transplantation. Present results are encouraging for designing a stemcell mediated delivery of Fe-Cr-Nb-B magnetic nanoparticles to solid tumour sites for hyperthermia applications.

Magnetic hyperthermia uses the targeted therapeutic heat from magnetic particles (MPs) in an alternating magnetic field to kill cancer cells. MPs with low Curie temperature (Tc) (in the range 42 °C–45 °C), high magnetization, and magnetic permeability/susceptibility are good candidates for their use in hyperthermia therapy. This paper analyzes the hyperthermic effects determined by the MPs with low Tc within a tumoral configuration from healthy tissue when an alternating magnetic field is applied. The temperature field was determined as a solution of the Pennes bioheat transfer equation. The spatial distribution of the particles after their injection within the tissues was computed by solving the convection–diffusion equation in porous tissues. Results show that the MP injection rate significantly influences the spatial distribution of the particles and the temperature field of the tumor. Higher values of the ferrofluid flow rate push more particles to the tumor center, thus also elevate its central temperature. The temperature field becomes uniform in a percentage of 90% of tumor volume if a blood vessel is localized at the tumor center.

Magnetic nanowires are potential candidates for substituting, within enhanced cochlear implants, the role played by hair cilia from the inner ear, which are responsible for the transduction of acoustic vibrations into electric signals. The sound waves pressure that is bending the magnetic wires induces stresses that are leading to changes in magnetic properties, such as magnetization and permeability. These changes can be detected by a GMR sensor placed below the nanowire array or, in the case of different designs, by a pick-up coil wrapped around the fixed-end of the wires. For the latter case, we are studying the stress distributions caused by bending deformations using the COMSOL finite element software package. We are also proposing a theoretical method for the evaluation of magnetic permeability variation vs. induced stress dependence. The study is performed on CoFeSiB amorphous micro- and nanowires subjected to mechanical perturbations similar to the ones produced by sound pressure waves.

The structural investigations of SrFe11.9In0.1O19 compound synthesized by solid-state method have been carried by neutron diffraction method in a wide temperature range. The appearace of spontaneous polarization that coexists with ferrimagnetic ordering has been found out at room temperature in strontium hexaferrite partially substituted with In ions. In order to explaine the presence of ferroelectric properties in SrFe11.9In0.1O19 compound, its crystal structure has been refined within the framework of both centrosymmetric P63/mmc (No. 194) and non-centrosymmetric P63mc (No. 186) space groups. The analysis of refinement results allows to understand microscopic mechanism of appearance ferroelectric properties in strontium hexaferrites., This project has received funding from the EU – H2020 research and innovation programme (support of the scientific infrastructure and scientific mobility for measurements in EU countries) under grant agreement No 654360 having benefitted from the access provided by CSIC/ICMAB in Barcelona (ES) and by CEA/LLB in Paris (FR) within the framework of the NFFA – Europe Transnational Access Activity. The work was support by the Russian Science Foundation (Agreement No. 19-19-00694 of 06 May 2019).

The magnetic and magnetotransport properties have been investigated in a family of multilayer glass-coated microwires with a soft CoFeSiB nucleus and magnetically harder Co and CoPtRh deposited outer layers. Their magnetic properties are mainly determined by the magnetic interactions between the magnetic phases, i.e., the magnetoelastic coupling generated by the supplementary mechanical stresses induced by the deposited layers and by the magnetostatic interactions between the soft magnetic inner core and the hard magnetic deposited layers. The deposition of 900 nm-thick hard magnetic layers (Co and CoPtRh) on the soft magnetic CoFeSiB glass-coated microwire leads to a biphase magnetic character. Isothermal annealing at 300 °C for 1 h of multilayer microwires determines a slight decrease of the coercive field, an increase in the relative magnetic permeability, and to an increase in the magnetoimpedance response, more significant for the CoFeSiB/Co multilayer microwires. The possibility to design the magnetic and magnetotransport properties through magnetic coupling and annealing makes these materials very competitive as the functional sensing elements.

The heating potential, cytotoxicity, and efficiency of Fe 68.2 Cr 11.5 Nb 0.3 B 20 magnetic nanoparticles (MNPs), as such or coated with a chitosan layer, to decrease the cell viability in a cancer cell culture model by using high frequency alternating magnetic fields (AMF) have been studied. The specific absorption rate varied from 215 W/g for chitosan-free MNPs to about 190 W/g for chitosan-coated ones, and an equilibrium temperature of 46 °C was reached when chitosan-coated MNPs were subjected to AMF. The chitosan-free Fe 68.2 Cr 11.5 Nb 0.3 B 20 MNPs proved a good biocompatibility and low cytotoxicity in all testing conditions, while the chitosan-coated ones induced strong tumoricidal effects when a cell–particle simultaneous co-incubation approach was used. In high frequency AMF, the particle-mediated heat treatment has proved to be a critical cause for decreasing in vitro the viability of a cancer cell line.

The magnetic characteristics of FINEMET type glass-coated nanowires and submicron wires are investigated by taking into account the structural evolution induced by specific annealing all the way from a fully amorphous state to a nanocrystalline structure. The differences between the magnetic properties of these ultrathin wires and those of the thicker glass-coated microwires and “conventional” wires with similar structures have been emphasized and explained phenomenologically. The domain wall propagation in these novel nanowires and submicron wires, featuring a combination between an amorphous and a crystalline structure, has also been studied, given the recent interest in the preparation and investigation of new materials suitable for the development of domain wall logic applications.

The temperature field developed by the magnetic nanoparticles injected directly within malignant tissues provides precious information about the main parameters which influence their heating mechanisms. This paper analyses the temperature field induced within a tumoral tissue by the Fe - Cr - Nb - B and magnetite systems, when an external time - dependent magnetic field is applied. An analytical temperature model which predicts the temperature in a tumoral tissue was developed. The particles with a lognormal size distribution were considered. The heat generation by Neel and Brown relaxations was modeled using the thermal and magnetic properties of the Fe - Cr - Nb - B particles experimentally determined. Fe - Cr - Nb - B magnetic systems have a particular behavior with the frequency and amplitude of the AC magnetic field. The temperature field can be controlled by tuning of the magnetic field parameters. As a result of their magnetic and thermal properties, these systems can be used for the magnetic hyper...

Quantitative results on the magnetostatic and magnetoelastic contributions in amorphous glass-coated Fe 77.5 Si 7.5 B 15 nanowires with positive magnetostriction are reported. The effects of wire dimensions on both terms have been analyzed. Calculated results have been interpreted in correlation with experimental data obtained from hysteresis loop measurements. The detailed analysis points to a single domain magnetic structure with an axial easy axis of magnetization, in which the origin of the axial magnetic anisotropy is magnetoelastic in the inner, main part of the nanowires, and magnetostatic in the thin, near-surface region. The values of the switching field are predominantly given by the magnetoelastic contribution.

Magnetic hysteresis of rapidly solidified amorphous glass-coated nanowires with nearly zero magnetostriction has been investigated to understand the origin of their bistable behavior. Experimental hysteresis loops and simulated ones have shown that shape anisotropy is responsible for the observed variation of the coercivity values with sample dimensions. The results of this paper provide thorough information about the main contributions to the magnetization reversal mechanism in amorphous nanowires prepared by glass-coated melt spinning.

Thermal processing of materials in external magnetic field is employed in order to produce a controllable uniaxial anisotropy and to tailor a domain structure in the series of soft magnetic FeCo-and FeNi-based amorphous/nanocrystalline alloys. Examples of our recent work on the utilization of both longitudinal and transverse magnetic field annealing for tuning the shape of hysteresis loops as well as the giant magnetoimpedance (GMI) characteristics are briefly presented. The beneficial effects of a heat treatment under magnetic field are discussed in terms of the improved application-oriented properties of these soft magnetic alloys.

Results concerning the influence of deposition conditions (effective power, P eff , pulse length, τ , and working gas pressure, p ) as well as of thermal treatments on the properties of Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 thin films, deposited by high power impulse magnetron sputtering (HiPIMS) technique, are presented. The P eff , τ and p values were varied in the range of 30–90 W, 4–20 μs and 8–60 mTorr respectively. According to the XRD analysis, in as-deposited state, all the prepared samples are amorphous. For P eff constant the coercive magnetic field, H c , increases whit τ , while for τ constant H c decreases when P eff increases. The lowest H c values have been obtained after the samples were annealed at temperatures between 450 °C and 480 °C, when the average size of the α-Fe(Si) grains and the crystalline volume fraction increase about 45% and 20% respectively.

The control of the temperature field within malignant tissues is an important task in the magnetic hyperthermia. The temperature analysis is a good method to focus the main parameters which can improve the heating mechanisms of the magnetic particles injected within tissues when the magnetic fields are applied. This paper analyses the temperature effects induced within tumoral tissues by the super-paramagnetic systems as FeCrNbB, magnetite and maghemite when an external time-dependent magnetic field is applied. A 3D temperature model which predicts the temperature field in a tumoral tissue was developed. The heat generation by Neel and Brown relaxations was modeled using the thermal and magnetic properties of the FeCrNbB particles experimentally determined. Interconnection between particle parameters (composition, size, magnetic and thermal properties), optimum dosage (volume concentration) and the magnetic field parameters (frequency and magnetic field intensity) was studied. The FeCrNbB magnetic systems have a particular behavior with the frequency and amplitude of the AC magnetic field. The temperature gradients induced within the tumor as a result of the heating in the magnetic field are smaller than the ones induced by the magnetite systems. This temperature behaviour can be an advantage in the controlled heating of the tumors.

This manuscript deals with the synthesis of new hydrophilic magnetite particles by employing a two-step method: in the first step magnetite particles with hydrophobic shell formed in presence of oleic acid–oleylamine complex through a synthesis in mass, without solvent, in a mortar with pestle were obtained; while in the second step the hydrophobic shell was interchanged with an aminosilane monomer. The influence of the Fe2+/Fe3+ molar ratio on the dimension of the particles of high importance for their potential applications was carefully investigated. This paper, also presents an alternative method of synthesis of new core-shell magnetite particles and the complete study of their structure and morphology by FT-IR, XPS, TGA, ESEM and TEM techniques. The rheological properties and magnetization analysis of high importance for magnetic particles were also investigated.

Using high-power impulse magnetron sputtering (HiPIMS) technique, Fe73.5Cu1Nb3Si15.5B7 thin films with thickness between 40 and 700 nm were deposited. The influence of deposition conditions (deposition time and argon pressure) and of the annealing temperature on the structure and coercive magnetic field of the magnetic films was analyzed. In the as-deposited state, the coercive magnetic field presents a minimum at about 10 mtorr argon pressure. The X-ray diffraction studies show that in the as-deposited state, the samples are amorphous, while after annealing at temperatures between 400°C to 525°C, α-Fe(Si) grains start to nucleate, the grain size varying from 2 to 18 nm. The Curie temperature of as-deposited amorphous phase and the onset of the primary crystallization are 355°C and 460°C, respectively. The lowest coercive magnetic field was obtained after annealing at 475°C.

In this paper we present the magnetic properties of mesoporous silica-coated Fe 3 O 4 nanoparticles. The coating of magnetite nanoparticles with mesoporous silica shell was performed under ultrasonic irradiation. The obtained mesoporous silica-coated magnetite nanoparticles were characterized by powder X-ray diffraction, focused ion beam-scanning electron microscopy, nitrogen adsorption–desorption isotherms and vibrating sample magnetometer. The hysteretic behavior was studied using first-order reversal curves diagrams. The X-ray diffraction result indicates that the extreme chemical and physical conditions created by acoustic cavitations have an insignificant effect on crystallographic structural characteristic of magnetite nanoparticles. Changes in the coercivity distributions of the magnetite nanoparticles were observed on the first-order reversal curves diagrams for the samples with coated particles compared with the samples containing uncoated particles of magnetite. The coated particles show an increased most probable coercivity of about 20% compared with the uncoated particles which can be associated with an increased anisotropy due to coating even if the interaction field distribution measured on the diagrams are virtually identical for coated/uncoated samples.

The effect of molar ratio of two hydrated iron salts used as precursors into a (co)precipitation-based synthesis method, on the composition, size and specific saturation magnetization of mixed iron oxides and oxyhydroxides magnetic nanoparticles as reaction products, was studied. The preparation procedure is based on a salt-assisted solid-state chemical reaction. The obtained products are magnetic multiphase components with the mean size ranging from 3 to 10 nm and specific saturation magnetization between 25 and 95.5 emu/g. The specific saturation magnetization modifies in a non-linear manner as the molar ratio of the iron salts varies. Excepting one sample, for which Fe2+/Fe3+ molar ratio was zero, all magnetic nanoparticles show a ferrofluid-like behaviour in the colloidal form. The small size, ferrofluid-like behaviour, and controlled specific saturation magnetization allow the use of new synthesized nanoparticles in specific biomedical or industrial applications.

The effect of the magnetic anisotropy and the dipolar interactions between NiFe magnetic layers and between nanowires on the magnetic properties of NiFe/Cu multilayered nanowire arrays electrodeposited into the nanopores of anodic aluminium oxide (AAO) templates with diameters of 35 and 200 nm has been studied. The variation of the aspect ratio (thickness/diameter) between the NiFe magnetic and Cu nonmagnetic layers influences the effective anisotropy field. The correlation between the measured hysteresis loops, with the applied field parallel and perpendicular to the multilayered nanowires’ axis, and the calculated effective anisotropy field, Heff, and saturation field, Hsat, shows that it is possible to tune the orientation of the magnetization axis with high accuracy. Two formulas, which include both the intra- and internanowire interactions, were proposed to calculate the saturation fields of multilayered nanowire arrays for the applied field parallel and perpendicular to the nanowires’ axis.

Nanocomposite NdFeB/αFe magnets were obtained by spark plasma sintering technique using high energy ball-milled Nd-Fe-B melt-spun ribbons mixed in different weight ratios with Fe commercial powders. The remanence of SPS nanocomposite magnets increases with the Fe powders content from 6.1 for 4 wt.% Fe to 6.4 kG for 5 wt.% Fe, while the estimated maximum energy product is also increased from 9.0 to 10.6 MGOe.

Phone: þ34 913349051, Fax: þ34 913720623Recognizing the importance of magnetic thin wires for scienceand technology, the 6th International Workshop on MagneticWires was held on 6–7 July 2010, in Bodrum, Turkey. A widerange of topics were addressed from technological problems ofmicro-andnanowirefabrication,toadvancedphysicaleffectsandnovel applications. Furthermore, critical discussions on thepresent state of knowledge and future trends arose during thePanel Session on microwires. In the present report, the mainaspects addressed at the Discussion Panel and at workshoppresentationsaresummarizedwiththeaimtostatethepresentandfuture perspectives on these wire systems. This report is focusedupon four topics chosen for broad discussions at the Panel:Fabrication and processing, Magnetization reversal and Dynam-ics, High-frequency properties, and Technological applications.

New silicon magnetite ferrofluids were prepared by dispersing siloxane-coated magnetite particles in polydimethylsiloxane with low or high molecular weights. Ferrofluids are stable colloidal dispersions of ultra fine covered magnetite particles, which may be selected for a specific application. We demonstrated new methods of stabilizing the magnetic particles by reacting the hydroxyl groups on the surface of magnetite particles with terminal ethoxy groups of polydimethylsiloxane, followed by their dispersion in silicon fluids. The new silicon ferrofluids were tested from the morphology, magnetic properties/losses, and rheological properties point of view.

In this work, two types of electrodeposited Ni–Fe /insulator/ Cu composite wires, namely Ni–Fe /seed layer/glass coated copper wire (Composite Wire A), and Ni–Fe /seed layer/sputtered SiO2/Cu (Composite Wire B), have been fabricated and their giant magneto-impedance effects have been investigated. With different implementations of the insulator layer, the magneto-impedance effect of Composite Wire A, whose insulator layer is cast from the melt Pyrex, is significantly higher than that of Composite Wire B with an insulator of sputtered SiO 2 layer. The profile of the insulator layer, as well as the thickness of magnetic layer and the diameter of the conductive core, greatly influences the interaction between the magnetic layer of Ni–Fe and the copper core, as shown in their giant magneto-impedance (GMI) effects. The maximum MI ratios obtained from Composite Wires A and B are 226% at 800 kHz when H ext = 0.87 Oe , and 95% at 1 MHz when H ext = 0 Oe , respectively. The Composite Wire A is a promising candidate for the sensing element of high sensitivity sensors to very weak magnetic field. For Composite Wire B, further improvement on its GMI effect and sensing performance requires optimization of its geometric parameters and the deposition conditions.

The magnetic dynamic interaction in ferromagnetic microwire arrays has been studied based on thin Co-based glass-coated amorphous microwires. The longitudinal hysteresis loops of the microwire arrays consisting of different number of wires have been measured statically with no current flowing through the arrays and dynamically with ac current flowing through the arrays. The results show that with the number of wires increases the transverse anisotropy of the arrays has been enhanced, especially when an ac current was applied to the arrays, an additional circumferential anisotropy was induced. The results are explained by a domain unification effect in the form of domain wall displacement. Moreover, the changes in the magneto-impedance effect with the number of wires in the arrays indicate that the domain unification effect is frequency dependant and related to the dimension of the arrays. The domain wall motion contributes to the magneto-impedance up to a critical frequency beyond which only domain rotation occurs. Below the critical frequency, the initial permeability of the arrays increases with the increase of the number of wires while above the critical frequency, the trend inverses. The magneto-impedance response of the microwire arrays is a consequence of the dynamic interaction of domain unification and eddy current.

Results concerning the influence of the additions of Ni and Ni–Si on the TMR response, saturating magnetic field and thermal stability of symmetric FeMn/FM/Al 2 O 3 /FM/FeMn MTJs, with FM=(Fe 0.58 Co 0.25 B 0.17 ) 100− x M x (M=Ni, Ni–Si), are presented. The magnetoresistance ratio for the symmetric Si/SiO 2 /Ta(5)/Ni 80 Fe 20 (5)/Fe 50 Mn 50 (8)/FeCoBNiSi(3.5)/Al 2 O 3 (1)/FeCoBNiSi(5)/Fe 50 Mn 50 (8)/Ta(5) MTJ structure was changed with about 9% in 20 G magnetic field, leading to a sensitivity of about 0.45%/G. This structure exhibits a field window of about 10 G and low values for the tunneling resistance of about 120 Ω and the thermal coefficient of resistance of about +60 ppm/°C.

A magneto-inductive prototype sensor based on magnetic amorphous wires which can detect surface cracks formed in ferromagnetic pieces is presented. The sensor consists of a very thin coil having a high permeability core made from Co 68.18 Fe 4.32 Si 12.5 B 15 amorphous wire with nearly zero magnetostriction and presents high sensitivity being able to detect both uniform magnetic field and localized gradient field. The inductance of the sensing coil, fed with an ac signal having a frequency of 150 kHz is changing dramatically with the applied magnetic field. As a consequence, excellent behavior of the magneto-inductive sensor having high sensitivity (60%/Oe) and high resolution was achieved. It is designed for nondestructive testing and specially for rail car bearing rings revision.

In this paper we present the results of applying the first-order reversal curves (FORC) diagram experimental method to the analysis of the magnetization processes of NdFeB-based permanents magnets. The FORC diagrams for this kind of exchange spring magnets show the existence of two magnetic phases—a soft magnetic phase and a hard magnetic one. Micromagnetic modeling is used for validating the hypotheses regarding the origin of the different features of the experimental FORC diagrams.

In this paper, we determined the effect of DC Joule-heating on magnetic structure of conventional amorphous wires starting from the stresses that appear during preparation process. For a specified value of applied electrical DC current to some amorphous wires, we have analyzed the thermal stresses that appear during the thermal treatment and we calculated the radius of axial magnetic domain (cylindrical inner core) that results after the preparation and annealing processes. We have obtained that: (a) the total stresses (owing to the successive heating, crystallization and cooling) depend strongly on the applied electrical DC current and the radius of the wires; (b) the axial magnetic domain is bigger for the wire having a bigger radius; (c) the cylindrical inner core enlarges significantly after DC Joule-heating; and (d) smaller internal stresses are obtained at smaller values of the wire's radius.

The structural “memory effect” of anionic clays was used to obtain layered double hydroxides (LDHs) with tailored magnetic properties, by loading iron oxides and/or spinel structures on iron partially substituted hydrotalcite-like materials. The obtained magnetic layered structures were further used as precursors for new hybrid nanostructures, such as aspirin–hydrotalcite-like anionic clays. Transmission electron microscopy (TEM) analysis shows that small iron oxide or spinel nanoparticles coexist with the fibrous drug particles on the surface of partially aggregated typical clay-like particles. The specific saturation magnetization of the loaded LDHs can be increased up to 70 emu/g by using specific post-synthesis treatments.

A new giant magneto-impedance (GMI) biosensor prototype based on a glass-coated microwires array is reported. The optimal measurement conditions and the influence of a liquid suspension of commercially available polymer-based magnetic microparticles on the magneto-impedance (MI) response of the array were studied. The relative change in MI response enlarges as the number of the active microwires increases. The highest variation of 35% was found for 10 active microwires, for a current intensity of 10 mA. Some possible applications of the biosensor prototype are outlined.

As known, the magnetic properties of AGCMs are determined by the radial, azimuthal and axial internal stresses induced during both the preparation process and the suitable thermal treatments of these microwires. In this paper we have proposed a theoretical model in order to determine the total internal stresses induced during the dc joule-heating thermal treatment (heating?crystallization?cooling). In this view (i) we have started from the internal stress values obtained in the preparation process, (ii) we have considered the supplementary axial tensile stresses due to the mechanical drawing of the microwire during the preparation process and (iii) we have taken into account the difference between the thermal expansion coefficients of metal and glass. We have found that (i) the maximum value of the axial stresses obtained after the thermal treatment is bigger than that obtained in the preparation process, the difference being about 450?MPa, (ii) the maximum values for the azimuthal and radial stresses decrease by and ?MPa respectively, (iii) the dimensions of the cylindrical inner core increase significantly (by ), which involves an increase of the degree of magnetic order in the AGCMs and consequently leads to the appearance of a large Barkhausen effect (LBE) in low axially applied magnetic fields and (iv) the reduced remanence increases from 0.90 to 0.95.

The model presented here allows us to find the temperature distribution in an amorphous ribbon through which a dc current passes. With this end in view, we have taken into account the most important dc Joule heating effects: conduction, convection and radiative heat losses as well as the structural changes that appear in the crystallization process. In the domain situated above the temperature that corresponds to the onset of the crystallization process, we have studied the thermal behavior of the sample and we have analyzed the kinetics of the crystallization phenomenon for both the isothermal process and for the nonisothermal crystallization process (based on the Johnson–Mehl–Avrami equation). The computed temperature values (corresponding to amorphous phase) are experimentally verified through magnetic measurements using a fluxmeter method (performed on amorphous ribbons with known Curie temperature), while those corresponding to the crystallization process are experimentally verified using differential scanning calorimetry analysis and X-ray difraction. We conclude that the dc Joule heating of ribbon is accurately described by this model, the analytically and numerically obtained results being in good agreement with experimental data. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A magnetic sensor based on the giant magnetoimpedance (GMI) effect for the detection of biomolecules was made with a CoFeSiB amorphous magnetic microwire as sensing element. Using soft ferromagnetic cobalt microparticles and field sensitivities of the impedance of about 2.5%/A m −1 in the very low field region (less than 200 A m −1 ) at frequencies close to 10 MHz, a highly sensitive response was measured, appropriate for the detection of low biomolecule concentrations.

The method of preparation and physical properties of Co 68.25 Fe 4.5 Si 12.25 B 15 amorphous microspheres, with special emphasis on the magnetic ones, are presented. Tissue tolerance was tested on Wistar white rats, and the results suggest that these amorphous magnetic microspheres are potential candidates for biomedical applications.

Displacement sensors of the toroidal transformer type with cores of amorphous ribbons from different alloys, namely Fe 77.5 Si 7.5 B 15 , Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 , and Co 68.25 Fe 4.5 Si 12.25 B 15 , have been manufactured and tested. The distance between the sensor and the proximity target is established by measuring the level of a medium-frequency signal transmitted by the transformer according to the distance between the transformer and a permanent micro-magnet target. We suggest some applications for distance measurement and also for the precise position identification. The outlined method ensures high levels of noise immunity.

The surface anisotropy distribution in conventional amorphous wires (CAW) and glass-coated microwires (GCAW) with nearly zero magnetostriction and nominal composition Co 68.15 Fe 4.35 Si 12.5 B 15 is analyzed by ferromagnetic resonance (FMR) measurements. The derivative resonance spectrum changes with applied tensile stress and torque. The surface anisotropy fields were calculated for both type wires. The experimental results are explained considering the coupling between magnetostriction and applied stress.

The thermal effects of Joule-heating treatment on Fe77.5Si7.5B15 amorphous glass-covered microwires (AGCMs) are examined and, taking into account the appropriate boundary conditions at the metal–glass interface, a general solution of the equation describing the evolution of the sample temperature in the course of electrical direct current (dc) Joule-heating is found.A theoretical and thermo-numerical model for the calculation of the distribution of temperature in an AGCM through which an electrical current (dc) passes has been developed. This was done for the amorphous state (for sample temperature values below that corresponding to the onset of the crystallization process) and also for the transition from the amorphous to the crystalline phase (for both isothermal and non-isothermal processes) using the Johnson–Mehl–Avrami model. In the non-isothermal crystallization process, three crystallization products (αFe(Si), Fe2B and Fe23B6) were found, corresponding to the three stages of this process.

The surface anisotropy distribution in conventional amorphous wires (CAW) with positive (Fe-based), negative (Co-based), and nearly zero magnetostriction (Co-based with a small amount of Fe addition) is analyzed by ferromagnetic resonance (FMR) measurements. The anisotropy distribution changes with composition and applied torque. The experimental results are explained considering the coupling between magnetostriction and applied torque.

Co, Ni and NiFe nanowire arrays were prepared by electrodeposition into nanometer-sized pores of anodic alumina and polycarbonate membranes using a two-electrode electrochemical cell. The morphology of the samples was investigated by means of scanning electron microscopy (SEM). The structural characteristics of the samples were examined using X-ray diffraction. Magnetic measurements were performed at room temperature, using a vibrating sample magnetometer (VSM) and showed the coercivity values for as-made samples range between 19 and 58 kA/m.

GMI was investigated in amorphous Co-rich glass-covered microwires with very low magnetostriction constant. Internal stresses, induced in the metallic core by the glass coating, substantially reduce the magnitude of GMI. To improve GMI properties magnetoelastic coupling was reduced by a careful choice of alloy composition and by subsequent Joule-heat treatment. The maximum magnetoimpedance, Δ Z / Z ≈600% measured at frequency 15 MHz, is already close to the theoretical value (1060%) and is one of the highest GMI amplitudes ever reported.

Magnetic properties of ferromagnetic amorphous glass-covered wires with positive, negative, and nearly zero magnetostriction are reviewed. It is shown that their peculiar magnetic characteristics originate during the specific preparation process through dimensions and induced internal stresses. The role of the magnetoelastic coupling on the domain structure formation and subsequently on the magnetization process is discussed, together with the tailoring possibilities of such magnetic materials.

Rapidly and slowly quenched Nd90−x Fex Al10 glassy alloys with thicknesses up to 3 mm were investigated comparatively by structural and magnetic measurements in the temperature range 5–800 K and external fields up to 9 T. The glass-forming ability decreases increasing Fe content. Room temperature coercivities of over 0.6 T are observed, depending on composition and external field. The huge increase of the coercive field up to 5.5 T at low temperatures as well as the dependence on the cooling rate are supposed to result from the non-collinear magnetic structures developed in these amorphous alloys. From DC and AC magnetic measurements combined with neutron diffraction results we conclude that the structure, which is quenching conditions dependent, consists of a packing of nanometer-sized clusters. The topological and magnetic structures of Nd90−x Fex Al10 melt-spun ribbons and cast rods in a wide range of temperatures and for different x values are modelled using the reverse Monte Carlo method (RMC). The hypotheses of a cluster model, in which exchange interactions, local random anisotropies and thermal effects are competing, are proposed.

In magnetic hyperthermia, the temperature control within the malignant tissues is an important step to increase the efficiency of the therapy. A temperature analysis is a good method to improve the heating process of the magnetic particles injected within tissues. This paper analyzes the thermal effects induced within malignant tissues by the magnetic systems like: magnetite and Fe-Cr-Nb-B when an external time-dependent magnetic field is applied. The heat generation by Neel and Brown relaxations was modeled using the thermal and magnetic properties of the Fe-Cr-Nb-B particles experimentally determined. A lognormal particle size distribution was considered for these magnetic systems with dimensions from 5 nm to 30 nm. After their injection at the center of the tumor, according to the solution of the transient convection-diffusion equation in a porous medium, the mass concentration of the particles within ferrofluid has a spatial and temporal distribution. The ferrofluid injection process was modeled using...