I.T. Iakubov

Nondiagonal impedance of amorphous wires with circular magnetic anisotropy

Abstract The effect of the nondiagonal magnetoimpedance of amorphous wires with low magnetostriction is studied experimentally and theoretically. The nondiagonal effect was observed and investigated. For a wire with circumferential magnetic anisotropy the tensor of magnetic permeability is obtained as a function of external magnetic field amplitude H and other parameters. A strong dependence of this quantity on H is shown in the domain of the external magnetic field, H ⩽ H A where H A is the anisotropy field. The nondiagonal component of the surface impedance is responsible for the measured effect.

Nonlinear magnetization reversal of Co-based amorphous microwires induced by an ac current

The magnetization reversal of ferromagnetic Co-based amorphous microwires carrying ac current is studied. The frequency spectra of the voltage V induced in the pick-up coil wound around the microwires were analysed and were found to depend on the ac current amplitude I0 and external longitudinal dc magnetic field He. The even harmonics are shown to dominate in the frequency spectra of V if the ac current amplitude exceeds some threshold value, which strongly depends on He. A high sensitivity of the even harmonic amplitudes to the longitudinal dc field is demonstrated. The experimental data are described in terms of the Faraday law and the quasi-static Stoner-Wohlfarth model. The results obtained may be of importance for the design of weak magnetic field sensors.

A laminate of ferromagnetic films with high effective permeability at high frequencies

The paper reports on development of magnetodielectric material with high microwave permeability. The material is a laminate of multi-layer permalloy films deposited onto a thin mylar substrate by magnetron sputtering. The deposited films are arranged into a stack and glued together under pressure to obtain the laminate. With the content of ferromagnetic component in the laminate being 22 % vol., its measured quasistatic permeability is 60. The peak value of imaginary permeability attains 50 and the peak is located near 1 GHz. As compared with the multi-layer films, which the laminate is made of, it exhibits lower magnetic loss tangent at frequencies below the magnetic loss peak and may therefore be useful for many technical applications. Lower low-frequency loss may be attributed to pressing of the glued sample. This rectifies wrinkling appearing due to sputtering of rigid multi-layer film onto flexible mylar substrate and, therefore, makes the magnetic structure of the film more uniform.

Laminates of Thin Ferromagnetic Films for Microwave Applications

Thin ferromagnetic films are known to exhibit the highest possible microwave permeability of known magnetic materials. Magnetic materials with high microwave magnetic performance are useful for many technical applications. However, bulk rather than planar materials are frequently needed for the applications. Bulk materials with high microwave permeability may be produced as laminated structures of thin ferromagnetic films, possibly patterned. The paper presents experimental data on the microwave permeability of such laminated structures based on Fe films. Possible technical applications of the materials under study include thin wideband radar absorbers and miniaturized patch antennas.

High-frequency magnetic permeability of nanocomposite film

Abstract The high-frequency magnetic permeability of nanocomposite film consisting of the single-domain spherical ferromagnetic particles in the dielectric matrix is studied. The permeability is assumed to be determined by rotation of the ferromagnetic inclusion magnetic moments around equilibrium direction in AC magnetic field. The composite is modeled by a cubic array of ferromagnetic particles. The magnetic permeability tensor is calculated by solving the Landau–Lifshits–Gilbert equation accounting for the dipole interaction of magnetic particles. The permeability tensor components are found as functions of the frequency, temperature, ferromagnetic inclusions density and magnetic anisotropy. The obtained results show that nanocomposite films could have a rather high value of magnetic permeability in the microwave range.

Effect of Perpendicular Anisotropy and Eddy Currents on the Microwave Performance of Single-Layer and Multi-Layer Permalloy Films

In this letter, microwave and magnetostatic measurements of single- and multilayer Permalloy films are made to find physical reasons causing the decrease of the microwave permeability of the films with increase in film thickness. The permeability is measured in the frequency range of 0.1-10 GHz by a coaxial technique. From the measured permeability, a contribution to the effective field from the magnetoelastic effect is determined. The decrease of microwave permeability in thick films is shown to arise mainly due to the perpendicular magnetic anisotropy rather than from the effect of eddy currents, as is frequently suggested. It is also shown that both these effects are reduced in multilayer films comprising alternating magnetic and dielectric layers. Therefore, such films are promising materials for developing magnets that possess high permeability at high frequencies.

Control over magnetic spectrum of multilayer magnetic film metamaterial

A RLC electric circuit with magnetic core is studied experimentally and theoretically as a promising design of a metamaterial cell. Laminates made of multilayered ferromagnetic films are used as the magnetic core. The wire coiled around the core allows the frequency dependence of permeability to be adjusted according to needs of a particular task by creating a region of intensive magnetic loss below the ferromagnetic resonance frequency of the bare core. The theoretic analysis is based on the quasi-statics of magnetic fields and electric currents. The intensity of the loss peak is proportional to the value of μ′2/μ″, where μ′ and μ″ are the frequency-dependent components of permeability of the core material. The magnetic spectra of cells with cores made of laminates of NiFe films and FeCo films have been measured. It is shown that the application of the winding allows the magnetic loss peak to be shifted from 1 GHz to 0.3 GHz for NiFe and from 5 GHz to 0.7 GHz for FeCo. The effective imaginary permeabilit...

Nonlinear magnetization reversal in copper-permalloy composite wires induced by a high-frequency current

The phenomenon of magnetization reversal in copper-permalloy composite wires induced by a high-frequency ac current field was studied. The frequency spectrum of a voltage measured in the probing coil wound on the wire contains only even harmonics in a broad range of amplitudes of the ac excitation current and the bias magnetic field strength. The amplitude of the even harmonics measured is highly sensitive with respect to the bias field. The results can be used to develop weak magnetic field sensors.