https://shell.cas.usf.edu/~phanm//PMS.pdf

Giant magnetoimpedance materials: Fundamentals and applications

The calculation of the residual stress tensor components in glass-coated amorphous ferromagnetic microwire is carried out on the basis of the theory of viscoelasticity. The approach takes into account the relaxation of the stresses both in a metallic core and a glass shell of the wire within a certain temperature interval near the point of the wire's vitrification. The distribution of the residual stresses is investigated as function of mechanical characteristics of metallic core and glass shell at different ratios of the metallic core radius to the total wire radius. The magnetic behaviour of a glass-coated amorphous microwire with small negative magnetostriction is analysed and is shown to be consistent with the experimental data.

https://iopscience.iop.org/article/10.1088/0022-3727/33/10/305/pdf

Residual quenching stresses in glass-coated amorphous ferromagnetic microwires

Recent advances in technology involving magnetic materials require development of novel advanced magnetic materials with improved magnetic and magneto-transport properties and with reduced dimensionality. Therefore magnetic materials with outstanding magnetic characteristics and reduced dimensionality have recently gained much attention. Among these magnetic materials a family of thin wires with reduced geometrical dimensions (of order of 1–30 μm in diameter) have gained importance within the last few years. These thin wires combine excellent soft magnetic properties (with coercivities up to 4 A/m) with attractive magneto-transport properties (Giant Magneto-impedance effect, GMI, Giant Magneto-resistance effect, GMR) and an unusual re-magnetization process in positive magnetostriction compositions exhibiting quite fast domain wall propagation. In this paper we overview the magnetic and magneto-transport properties of these microwires that make them suitable for microsensor applications.

https://www.mdpi.com/1424-8220/9/11/9216/pdf

Thin Magnetically Soft Wires for Magnetic Microsensors

Stratum corneum is the main obstacle for drugs to pass through the skin. Microneedles are composed of arrays of micro-projections formed with different materials, generally ranging from 25–2000 μm in height. Microneedles straightly pierce the skin with its short needle arrays to overcome this barrier. Microneedles can be divided into several categories, for instance, solid microneedles, coated microneedles, and hollow microneedles and so on. However, all these types have their weak points related to corresponding mechanisms. In recent years, pioneering scientists have been working on these issues and some possible solutions have been investigated. This article will focus on the microneedle arrays consisting of hydrogels. Hydrogels are commonly used in drug delivery field. Hydrogel microneedles can be further divided into dissolving and degradable microneedles and phase transition microneedles. The former leaves drug with matrix in the skin. The latter has the feature that drugs in the matrix are delivered while the remaining ingredients can be easily removed from the skin after usage. For drugs which are required to be used every day, the phase transition microneedles are more acceptable. This article is written in order to summarize the advantages of these designs and summarize issues to be solved which may hinder the development of this technology.

https://link.springer.com/content/pdf/10.1007%2FBF03353783.pdf

Hydrogel Microneedle Arrays for Transdermal Drug Delivery

The magnetoelastic sensor based on the stress dependence of the GMI effect in Co 68.5 Mn 6.5 Si 10 B 15 amorphous microwire has been introduced. This amorphous microwire after adequate heat treatment shows the maximum GMI ratio (Δ Z / Z ) m up to around 130%. GMI effect of this microwire has been found to be affected by the magnetoelastic anisotropy induced in the sample by the applied tensile stress. This stress dependence of the GMI induces changes on the ac voltage measured between the ends of the sample placed in the magnetic field under applied tensile stress. When the sample is under a load of 3 g such change of the ac voltage across the microwire is about 3.5 V.

Magnetoelastic sensor based on GMI of amorphous microwire

Glass-coated amorphous microwires of two different compositions, and , with square hysteresis loops have been prepared and studied. The effect of applied tensile stress on their magnetic properties is reported for both kinds of microwires with radii of the metallic nucleus in the range from 1.9-m and thicknesses of the coating of 3.8-m. The switching field of the studied microwires depends on the sample's geometry (the radius of the metallic nucleus and the thickness of the glass coating), exhibiting a decrease with decreasing thickness of the coating owing to the induced internal stresses. For Fe-rich compositions an increase of the switching field with the applied tensile stress in the range of 0-750 MPa was observed, such an increase being more significant for a thin coating. The classical square root dependence of the switching field on the applied stress is found for Fe-rich compositions for the range of thicker metallic nuclei. Co-rich microwires exhibit quite a different stress dependence of the switching field, exhibiting first roughly stress-independent behaviour and then an increase with the stress. Removal of the glass coating results in a drastic change of the switching fields for both compositions, indicating the existence of strong internal frozen-in stresses. The observed experimental dependences were explained in terms of a dependence of the nucleation field both on external and on internal stresses and by taking into account the dependence of the magnetostriction constant on the strength of the total stresses.

https://iopscience.iop.org/article/10.1088/0022-3727/31/21/009/pdf

The stress dependence of the switching field in glass-coated amorphous microwires

The effect of external tensile stress on the hysteresis loops of nearly-zero magnetostrictive glass-coated amorphous microwires of (Co 100− x Mn x ) 0.75 Si 10 B 15 (10 x 56.5 Fe 6.5 Ni 10 B l6 Si 11 compositions of metallic nucleus has been studied. All hysteresis loops have a rectangular shape without applied stress. Significant changes in the shape of the hysteresis loop are produced by the application of tensile stress, particularly the hysteresis loop of the sample (Co 92 Mn 8 ) 75 Si 10 B 15 under a loading of 10 g, becoming flat with reduced values of both remanence and coercivity. These changes of the hysteresis loop with the external strain have been used to design a magnetoelastic sensor of liquid level.

Magnetoelastic sensor of liquid level based on magnetoelastic properties of Co-rich microwires

Structural and magnetic properties of amorphous and nanocrystalline Fe–Si–B–P–Nb–Cu alloys produced by gas atomization

We have performed experimental and theoretical studies on the influence of ac magnetic field amplitude on the magnetoimpedance tensor in an amorphous wire with helical magnetic anisotropy. For the experimental measurements, we used an amorphous wire of composition (Co/sub 0.94/Fe/sub 0.06/)/sub 72.5/Si/sub 12.5/B/sub 15/ with negative, nearly zero magnetostriction constant, excited either by an ac circular h/sub /spl phi// or by an axial h/sub z/ magnetic field created by an ac electric current. We changed the ac current amplitude from 7.5 to 40 mA and the current frequency f from 1.5 to 20 MHz. The values of the asymmetric giant magnetoimpedance ratio associated with the sweeping direction of the dc field H/sub ex/ and the corresponding sensitivity were 211% and 0.64 V/Oe, respectively, for an ac current of 37.5 mA at 3 MHz. For the theoretical study based on the magnetization rotation, we obtained the second-order harmonic of the ac magnetization m/spl I.oarr//sup (2)/ induced by the relatively high ac magnetic field by solving the Landau-Lifshitz-Gilbert (LLG) equation. We also considered a second-order surface impedance tensor /spl sigmav//spl circ//sup (2)/, which allowed us to analyze quantitatively the influence of the ac magnetic field amplitude on the impedance tensor of the wire. We obtained the domain model of the wire with helical magnetic anisotropy having multidomains and the magnetization vector /spl plusmn/M/sub 0/ directed in the easy direction, and the corresponding static magnetic configurations, by solving the static LLG equation. For the given magnetic configurations, we calculated the second-order impedance tensor /spl sigmav//spl circ//sup (2)/. The results can well explain the irregular field characteristics of the voltage responses at low dc field value, when the wire was excited at high frequency and at large ac magnetic field.

Influence of AC magnetic field amplitude on the surface magnetoimpedance tensor in amorphous wire with helical magnetic anisotropy

Particular aspects concerning Matteucci effect of four amorphous microwires (Fe/sub 58.9/Co/sub 14.7/Si/sub 16.2/B/sub 10.2/, Fe/sub 71.8/B/sub 9.1/Si/sub 14/Cu/sub 1/Nb/sub 3.1/, Co/sub 69/Mn/sub 7/Si/sub 10/B/sub 15/ and Co/sub 69/Mn/sub 6/Si/sub 10/B/sub 15/) with different values and sign of the saturation magnetostriction are reported. The effect of applied torque on the voltage of the Matteucci effect and the coercive field corresponding to the circular magnetization and axial magnetic field has been also measured and analysed considering the magnetoelastic helical anisotropy introduced by the torsion.

L. Dominguez

Papers

The stress dependence of the switching field in glass-coated amorphous microwires

Magnetoelastic sensor of liquid level based on magnetoelastic properties of Co-rich microwires

Structural and magnetic properties of amorphous and nanocrystalline Fe–Si–B–P–Nb–Cu alloys produced by gas atomization

Influence of AC magnetic field amplitude on the surface magnetoimpedance tensor in amorphous wire with helical magnetic anisotropy

Matteucci effect in glass coated microwires