Imaginary Part Of Magnetic Permeability Research Articles

Shielding performance of MnxNi0.8–xZn0.2Fe2O4 (0.1≤x≤0.7) for electromagnetic interference (EMI) in X-band frequency

A series of MnxNi0.8–xZn0.2Fe2O4 (0.1≤x≤0.7) nanoferrites were prepared by sol-gel auto combustion method. The TGA-DSC studies revealed the weight loss up to 700 °C and after no weight loss was found confirming the complete ferrite phase. Therefore, the as-burnt samples subjected to conventional sintering at 900 °C for 2h. The traces of XRD patterns revealed that formation of ferrite phase co-existed with secondary phases. The complex permittivity and permeability of present ferrite systems are found to be dependent of Mn2+ ion concentration. The real part of dielectric constant (ε′) for the all compositions are in the range of 5.184–6.951 at 8.2 GHz while it is 5.269–7.663 at 12.4 GHz. The values of ε′ at 8.2 GHz are slightly lower than the values at 12.4 GHz. The imaginary part of dielectric constant (ε″) was found to be in the range of 0.046–0.315 for all compositions over the entire range of X-band frequency (8.2–12.4 GHz). Compared to the variation of ε′, the variation of ε″ is more disorder. The number of semicircles in Cole-Cole plots is a witness of multiple di-electric relaxations of EM energy dissipation. The real part of magnetic permeability (μ′) is increasing, while imaginary part of magnetic permeability (μ″ ) is decreasing for all compositions as frequency is increasing from 8.2 to 12.4 GHz. Compared to the other ferrite compositions, the ferrite with low content of Mn2+ i.e. Mn0.1Ni0.7Zn0.2Fe2O4 ferrite system has higher value of μ″ and seems to be invariant over the entire X-band frequency range. The total effective shielding (SET) for all compositions is found to be in the range 37–12 dB. The highest values of SET 37 dB at 8.2 GHz and 28 dB at 12.4 GHz were reported for the ferrite composition Mn0.1Ni0.7Zn0.2Fe2O4. The shielding studies revealed that Mn–Ni–Zn ferrite systems are effectively suppressing electromagnetic interference (EMI) in X-band frequency. Comparatively, the ferrite system Mn0.1Ni0.7Zn0.2Fe2O4 is useful for the fabrication of EMI suppressor.

Numerical response and causality study of the magnetic permeability-frequency function of NiZn ferrites using Genetic Algorithm

The magnetic permeability of a ferrite is an important factor in device design such as inductors, transformers and microwave absorbent materials. In this paper, the magnetic permeability of NiZn ferrites doped with yttrium was simulated as a function of frequency using a magnetic permeability model, which contains six parameters that depend on the material. The model’s parameters were adjusted using the Genetic Algorithm. Genetic Algorithms are probabilistic search procedures that generate solutions to optimization problems using techniques inspired in biological evolution. The convenience of the Genetic Algorithms method is it that does not require estimated initial values for the parameters, which allows to find a stable global minimum.The magnetic loss of a NiZn ferrite was numerically investigated by using the Kramers-Kronig relationships. Due to the principle of causality and time independence in the relation between magnetization vector M and magnetic field H, the real and the imaginary part of the complex magnetic permeability are mutually dependent, and the correlation is given by Kramer-Kronig equations. In this paper, the imaginary part of the magnetic permeability was obtained numerically by applying the Hilbert transform to the simulated real part. Causality was suitably verified through the KK relationships.

Temperature Sensibility of Complex Permittivity in Ni–Zn Ferrite at Different Temperatures in the 700 MHz–1 GHz Range

This paper presents a study on the behavior of complex permeability and permittivity of a Ni-Zn ferrite, at temperatures between -40 °C and 50 °C, in frequencies from 1 MHz to 3 GHz. Complex permeability and permittivity data are presented for this frequency range. We observed that the real part of permittivity (e' ) has low-temperature sensibility from 700 MHz up to 1 GHz, caused by the overlapping of two different relaxation processes, and the definition of a thermal coefficient of e' corroborated these results. Outside this frequency range, temperature variations have a greater influence in permittivity. Havriliak-Negami functions were used to describe e behavior for each measured temperature. The measurements of the real and imaginary parts of magnetic permeability μ' and μ'' showed that they decrease with frequency, which is the typical behavior for this ferrite, and that lower temperatures have higher values for both μ' and μ'' after 50 MHz.

Green’s function theory of ferromagnetic resonance in magnetic superlattices with damping

We explore a quantum Green’s-function method to study the resonance absorption of magnetic materials. The relationship between the resonance magnon (spin wave) density and the resonance frequency of a superlattice consisting of two magnetic layers with damping and antiferromagnetic interlayer exchange coupling is studied. The effects of temperature, interlayer coupling, anisotropy, external magnetic field and damping on the the resonance frequency and resonance magnon density are investigated. The resonance excitation probability for a magnon is proportional to the resonance magnon density. In the classic methods, the imaginary part of magnetic permeability represents the resonance absorption in magnetic materials. In the quantum approach, the resonance magnon density can be used to estimate the strength of the resonance absorption. In the present work, a quantum approach is developed to study resonance absorption of magnetic materials and the results show the method to obtain a magnetic multilayered materials with both high resonance frequency and high resonance absorption.

Proposal for an active electromagnetic metamaterial based on spin-torque oscillators

We propose theoretically an active material for electromagnetic radiation with frequency of GHz by use of spin-torque oscillators. The origin of the amplification is the energy supplied to the magnetization by the injected current. We show that close to a resonance with current-driven magnetization, the imaginary part of magnetic permeability becomes indeed negative for either of the two circular polarizations, resulting in a negative imaginary part of the refractive index. Besides, the real part of the refractive index is also manipulated by the current. Our system thus realizes an active filter to obtain circular polarized radiation and/or an electromagnetic metamaterial having negative refractive index, both controlled electrically.

Nonuniform Magnetic States and Electrical Properties of ${\rm Sm}_{\rm X}{\rm Mn}_{1-{\rm X}}{\rm S}$ Solid Solutions

The real and imaginary parts of magnetic permeability at the three frequencies 100 Hz, 1 kHz and 10 kHz and magnetic moment in magnetic field H = 0.05 T in the SmXMn1-XS(0.1 ≤ × ≤ 0.25) solid solutions at the temperatures 5 K-300 K were measured. Magnetization curves were measured in the range of fields - 9 T <; H <; 9 T at the temperatures T = 5 K, 50 K. Non-linear behavior of the magnetization versus field, residual magnetic moment, logarithmic dependence of imaginary parts of the magnetic permeability maximum on frequency and sharp drop of Im(μ) at T <; 40 K for compound Sm0.25Mn0.75S were found. The electrical resistivity of the SmXMn1-XS(0.15 <; x <; 0.25) solid solution in the range of temperatures 80 K-300 K were measured. Minimum and maximum in the temperature dependence of the resistivity were found respectively at T = 220 K for X = 0.15 and at T = 100 K for X = 0.2 compounds. This behavior is explained a result of the mobility edge movement and the disorder of the deformation and spin density fluctuations with short-range order.

Induced magnetic anisotropy in Co-doped Finemet-type nanocrystalline materials

Transverse magnetic anisotropy has been induced in the Fe 14.7Co 58.8Cu 1Nb 3Si 13.5B 9 and Fe 13.8Co 65Cu 0.6Nb 2.6Si 9B 9 amorphous ribbons by annealing under an external magnetic field. This anisotropy plays a predominant role, compared to magneto-crystalline and magneto-elastic anisotropies, in forming the magnetic properties and shaping the hysteresis loop. The effect of temperature and time of annealing on the induced magnetic anisotropy and magnetic properties (magnetic permeability, coercivity and power losses) in both alloys was investigated. Under this work, measurements of frequency dependence of the real and imaginary parts of magnetic permeability were made within a frequency range up to 110 MHz. It was found that as a result of magnetic field annealing the Snoek limit increases in both alloys compared to the Co-free Finemet.

Causality study and numerical response of the magnetic permeability as a function of the frequency of ferrites using Kramers–Kronig relations

Abstract In this paper, the numerical treatment of magnetic loss of NiZn, MnZn, Ni 2 Y, and NiZnCu ferrite and their composites, by using Krameres–Kronig relations, is investigated. The complex magnetic permeability spectra for ferromagnetic materials have been studied. Due to the principle of causality and time independence in the relation between magnetic induction B and magnetic field H , the real and the imaginary part of the complex magnetic permeability are mutually dependent, and the correlation is given by the Krameres–Kronig equations. Through them, it is possible to measure the real component of the complex magnetic permeability, assuming the real component is given, and by the Hilbert transform, the imaginary part of the magnetic permeability can be calculated. Magnetic circuit model has been studied theoretically, focusing on the model's poles in the complex plane to verify the principle of causality and the temporary independence.

Magnetic loss in the nickel-zinc-iron oxide system

The formation of cubic inverted spinel structures in the nickel-zinc-iron oxide system produces ferrites with high initial magnetic permeability. However, the electrical conductivity of nickel-zinc ferrites, when prepared under oxidizing conditions, is extremely low. Consequently, the imaginary part of the dielectric constant is correspondingly low, and the resultant rf electric loss is small. Most loss is, therefore, associated with the imaginary part of the magnetic permeability, which declines inversely with frequency in the VHF-UHF frequency regime. In this work, dielectric constant and magnetic permeability were measured for a series of nickel oxide-zinc oxide-ferric oxide compositions in order to identify the region of the ternary diagram associated with higher values of magnetic loss. Ferrites were prepared under identical conditions by a reactive sintering process at 1200 °C. Compositions corresponded to stoichiometric spinels (NixZn1−xFe2O4), or to spinels with the presence of excess or insufficient ferric oxide. Toroids were machined for coaxial analysis. Variation of the imaginary part of permeability with ferric oxide concentration indicated that larger values of magnetic loss were obtained when a relatively large excess of Fe2O3 was absent. When values of the imaginary part of magnetic permeability were plotted versus the nickel-zinc atom ratio, the sensitivity was relatively weak near and above unity. Below a ratio of 0.75, magnetic loss decreased rapidly, disappearing below the ratio Ni/Zn≂0.2. Reasons for this behavior are discussed. The largest μ″ obtained with the stoichiometric iron oxide series was at Ni0.5Zn0.5Fe2O4.