Amorphous Ferromagnetic Microwires Research Articles

Microwave metamaterials with ferromagnetic microwires

This paper discusses a new type of wire media based on amorphous ferromagnetic microwires. The combination of two effects, namely, a strong dispersion of the effective permittivity in metallic wire composites (resonance or plasmonic type) and giant magnetoimpedance effect in wires, will result in unusual property that an effective dielectric response may strongly depend on the wire magnetization which can be changed with external stimuli: magnetic field, mechanical stress and temperature.

Microwave Metamaterials Containing Magnetically Soft Microwires

ABSTRACTThis paper discusses a new type of wire media based on amorphous ferromagnetic microwires. The combination of two effects, namely, a strong dispersion of the effective permittivity in metallic wire composites (resonance or plasmonic type) and giant magnetoimpedance effect in wires will result in unusual property that an effective dielectric response may strongly depend on the wire magnetization which can be changed with different external stimuli. We have demonstrated the effect of the external magnetic field on microwave response from composites containing CoFeSiBCr amorphous wires in free space at microwave frequency.

Magnetization switching in ferromagnetic microwires

Magnetization states of amorphous soft ferromagnetic microwires are studied by experiment and theoretically. It is shown that in low applied axial fields, on increasing the circular magnetic field produced by current, the initial homogeneous circular magnetization distribution evolves in three sequential steps: (i) the appearance of a helical magnetization state, (ii) a jump to the helical state with opposite chirality, and (iii) a gradual rotation of magnetization toward the new circular state. An applied, large-enough axial field stabilizes the axial magnetization states, making these transitions continuous and shifting the magnetic hysteresis loops. The origin of these successive magnetization reorientations and switching is explained in the frameworks of the proposed model.

Left handed material based on amorphous ferromagnetic microwires tunable by dc current

Tuning of the transmission characteristics of amorphous ferromagnetic microwires through a dc current is demonstrated. These structures are studied in the frequency region where they present double negative behavior. It is found that their frequency response shifts with small dc currents circulating along the wires. It is observed that the dc current tends to compensate and even cancels the resonant peak associated to the static magnetic field applied along the wire axis. The phenomenon behind these findings is discussed in terms of the torque exerted by the field created by the current on the plane perpendicular to the wire axis.

An automated compact vibromagnetometer for investigating soft magnetic materials

An automated vibration magnetometer for measuring the magnetization and hysteresis curves of soft magnetic materials at room temperature is described. The vibromagnetometer has a magnetic moment sensitivity of 5∙10 -6 Gs∙cm 3 , a measurement error of less than 3% and a magnetizing field strength range of up to ±200 Oe, which can be extended to ±10000 Oe using more powerful magnetic systems. Hysteresis characteristics of amorphous ferromagnetic microwire and of a printed text sign are presented.

Metamaterials from Amorphous Ferromagnetic Microwires: Interaction between Microwires

For inhomogeneous mediums the оptical Magnus effect has been derived. The metamaterials fabricated from amorphous ferromagnet Co-Fe-Cr-B-Si microwires are shown to exhibit a negative refractive index for electromagnetic waves over wide scale of GHz frequencies. Optical properties and optical Magnus effect of such metamaterials are tunable by an external magnetic field.

Metamaterials Fabricated of Amorphous Ferromagnetic Microwires: Negative Microwave Permeability

Microwave permeability of glass-coated ferromagnetic amorphous microwire exhibiting a weak negative magnetostriction has been studied. The diameter of the microwire was about 20 m and the diameter of the metal core was about 12 m. The microwire was wound to comprise a 7/3 washer-shaped composite sample with the volume fraction of magnetic constituent of about 10%. The permeability of the composite sample was measured in a coaxial line in the frequency range from 0.1 to 10 GHz. The composite was found to exhibit a negative permeability within the frequency range from approximately 0.7 to 1.5 GHz, with the permeability being as low as −0.4. Therefore, microwire-based composites, particularly, crossed arrays of microwires may be employed to develop metamaterials for microwave applications. In the composite, the negative microwave permeability is due to the natural ferromagnetic resonance and the negative microwave permittivity is due to the inherent inductance of the wire. Such metamaterials are advantageous in simple design, isotropic in-plane performance, and possible tunability of performance by external magnetic bias. However, for a feasible metamaterial fabricated from microwire arrays, the wires have to exhibit higher magnitude of the ferromagnetic resonance, higher quality factor, and higher resonance frequency.

Metamaterials with Tunable Negative Refractive Index Fabricated from Amorphous Ferromagnetic Microwires: Magnetostatic Interaction between Microwires

For inhomogeneous mediums the optical Magnus efiect has been derived. The metamaterials fabricated from amorphous ferromagnet Co-Fe-Cr-B-Si microwires are shown to exhibit a negative refractive index for electromagnetic waves over wide scale of GHz frequencies. Optical properties and optical Magnus efiect of such metamaterials are tunable by an external magnetic fleld, magnetic fleld from neighbourhood microwires and mechanical stress.

Glass-coated amorphous ferromagnetic microwires at microwave frequencies

The objective of the present investigation is to outline some of the more relevant microwave properties of glass-coated amorphous magnetic microwires. The introductory section includes a brief description of the quenching and drawing preparation procedure that determines their cylindrical shape, their amorphous nature and the presence of the glass coating. The shape and magnetoelastic (stresses and magnetostriction) anisotropy terms imposed by those characteristics finally determine the microwave properties. Subsequently, a description is given of the circumferential, parallel and transverse excitation configurations of the electric and magnetic fields in the study of microwave response. The dynamic properties of the microwires are discussed for the three configurations. Particularly, the correlation between giant magnetoimpedance effect and ferromagnetic resonance (FMR) at various working frequencies is analysed for the circular magnetic field configuration. The influence of magnetoelastic anisotropy through mechanical stresses is investigated through the changes in the parallel permeability for microwires with different coating thickness. The role of magnetoelastic anisotropy through the magnetostriction constant is analysed through the scattering parameters and the change of FMR frequency for microwires with different alloy composition. Finally, the electromagnetic properties of microwires embedded in polymeric matrices are envisaged.

Microwire Magneto-Resonance Characteristics in a Magnetic LC-Resonator Device

In the present work, the magneto-resonance characteristics in a LC -resonator device built on amorphous glass-coated Co-based ferromagnetic microwires have been investigated. The giant magnetoimpedance (GMI) measurements were conducted in the high-frequency range of 100 { 800 MHz and for a dc magnetic eld varying within 120 Oe. The variation in the diameter of the microwire had signi cant e ects on the magnitude of the GMI e ect, the characteristic resonance frequencies and the positions of the resonant peaks. The resonance in a LC -resonator device occurs at a speci c intensity of the applied dc magnetic eld. Noticeably, the largest eld sensitivity of the GMI reaches extremely high values of 20,000 %/Oe and 18,000 %/Oe at resonance frequencies of 518.21 MHz and 146.25 MHz for LC -resonators constructed using Co83:2B3:3Si5:9Mn7:6 and Co67Fe3:8Ni1:4B11:5Si14:6Mo1:7 microwires, respectively. These results are of great interest for developing a new class of ultra-sensitives, high-frequency GMI-based magnetic sensors.

Magnetic and microwave properties of glass-coated amorphous ferromagnetic microwires

Glass-coated amorphous FeCuNbSiB microwires were prepared by Taylor-Ulitovsky technique. X-ray diffractometry and scanning electron microscopy were used to investigate the microstructure and morphology of the glass-coated microwires respectively. The vibrating sample magnetometer and vector network analyzer were used to study the magnetostatic and microwave properties of glass-coated microwires. The experimental results show that the effective anisotropy of an array of 150 microwires of 10 mm in length is large than that of one microwire of 10 mm in diameter and an array of 150 microwires of 1 mm in diameter. The natural ferromagnetic resonance takes place as the microwave magnetic component is perpendicular to the microwires axis, and the electric dipole resonance takes place as the microwire is long or the short microwire concentration is moderate. The natural ferromagnetic resonance shifts to higher frequency with the larger microwire concentration. The electric dipole resonance is governed by the microwires length and concentration. The glass-coated FeCuNbSiB microwires can be used to design EMI filters and microwave absorbing materials.

Optical Magnus effect in metamaterials fabricated from ferromagnetic microwires

In homogeneous negative phase velocity media, the Doppler and Cherenkov-Vavilov effects and the refraction and pressure of light are anomalous: they are inverse with respect to the corresponding effects in conventional media. Using the geometrical optics approximation, it is shown that the optical Magnus effect in inhomogeneous negative phase velocity media is also anomalous. The effect is demonstrated by considering a metamaterial consisting of parallel amorphous ferromagnetic microwires in a magnetic field. The metamaterial proves to be a left-handed one in the realistic region of the electromagnetic spectrum. The optical properties of such a left-handed medium can be controlled by the external magnetic field.

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We studied the effect of annealing conditions on magnetic properties of amorphous CoFeNi-based glass-coated microwires. We showed that annealing can be very effective for manipulation of the magnetic properties of amorphous ferromagnetic glass-coated microwires. Low coercivity and high Gaint magnetoimpedance (GMI) effect have been observed in as-prepared Co-rich microwires. After annealing of Co-rich we can observe transformation of linear hysteresis loops to rectangular and coexistence of fast magnetization switching and GMI effect in the same sample. We demonstrated that the coercivity of microwires can be tailored by annealing in the range from 4 to 200 A/m. We found that the annealing considerably affects the magnetostriction coefficient and observed correlation between the magnetic hardening of studied microwires and the magnetostriction sign change.

Microwave permeability of metamaterials based on ferromagnetic composites

In this paper, we focus on metamaterials based on ferromagnetic composite combined with an inductive pattern. CoFeSiB amorphous ferromagnetic glass-coated microwires and thin films are involved in the composite. The inductive pattern is a coiling of Copper wire with a varying number of loops. We derived the microwave permeability of the ferromagnetic material inside the inductive pattern through a Landau–Gilbert model of gyromagnetism. In agreement with experimental results, the engineering of resonance frequency of the sample is achieved through the number of loops of the coiling.

Microwave permeability of amorphous ferromagnetic glass-coated microwires from 150 K to 450 K

Microwave permeability spectra of ferromagnetic glass-coated microwires at room temperature have already been studied. Using a new setup that we have recently developed, permeability spectra of ferromagnetic microwire at various temperatures are presented. CoFeSiB soft ferromagnetic microwires are studied from 150 K to 450 K, showing large changes in their permeabilities between 30 MHz and 3 GHz.

Amorphous ferromagnetic microwire in the microwave cavity. Ferromagnetic resonance and absorption

Ferromagnetic resonance (FMR) in amorphous ferromagnetic microwire in glass coating (AMW) was investigated. Two modes of FMR, caused by connections of precession of magnetization and natural electromagnetic oscillations of a sample as a microwave resonator was found out. It was shown that the excitation of FMR was caused by microwave magnetic field of induction currents connected to electrical component of fallen electromagnetic radiation. The magnetic constants of Fe 15Co 60B 10Si 15 microwire were determined at room temperature. All observable features of ferromagnetic resonance could be described in the frameworks of the used model.

Residual quenching stresses in glass-coated amorphous ferromagneticmicrowires

The calculation of the residual stress tensor components inglass-coated amorphous ferromagnetic microwire is carried out on the basisof the theory of viscoelasticity. The approach takes into account therelaxation of the stresses both in a metallic core and a glass shell of thewire within a certain temperature interval near the point of the wire'svitrification. The distribution of the residual stresses is investigated asfunction of mechanical characteristics of metallic core and glass shell atdifferent ratios of the metallic core radius to the total wire radius. Themagnetic behaviour of a glass-coated amorphous microwire with smallnegative magnetostriction is analysed and is shown to be consistent withthe experimental data.

Magnetoelastic behavior of glass-covered amorphous ferromagnetic microwire

Particular aspects concerning the magnetoelastic behavior of an Fe-rich glass-covered amorphous ferromagnetic microwire (diameter about 20 /spl mu/m) are reported in both the as-prepared state and after various heat treatments. The main feature of such behavior is that related with the bistable behavior exhibited by the microwire. The magnetization process takes place by a single and large Barkhausen jump at a given applied field. For the as-prepared material, the value of this switching field (H*/spl ap/112 Am/sup -1/) is about one order of magnitude larger than that reported for Fe-rich amorphous wires with a diameter of about 125 /spl mu/m (H*/spl ap/8 Am/sup -1/). The effect of the thermal treatment as well as the stress dependence of H* for as-obtained and treated microwire are also reported and discussed in terms of the stress distribution within the microwire.

Magnetic bistability of glass-covered Fe-rich amorphous microwire: influence of heating treatments and applied tensile stress

The influence of heat treatments and mechanical stresses on the magnetic behaviour of an Fe-rich glass-covered amorphous ferromagnetic microwire (diameter about 20 mm) is reported here. The behaviour is characterized by a magnetization process with a single and large Barkhausen jump at a given applied field. For the as-prepared material, the switching field corresponding to this bistable behaviour is around 100 A m−1 and can be significantly modified by adequate heating treatments as well as by application of mechanical stresses. These changes are discussed in terms of the modification of the internal stresses.