Magnetic Permeability Properties Research Articles

Influence of Mg(II) substitution on the structural, magnetic, and permeability properties of R-type hexagonal ferrites

A series of single-phase R-type hexagonal ferrites with the composition Sr1-xMgxFe4Sn2O11 (x = 0.0, 0.1, 0.2, 0.3) were manufactured using the auto-combustion sol-gel method sintered at 800 °C. The objective of this work was to study the effect of Mg additives on the structural, magnetic, and permeability properties of the synthesised material. The X-ray diffraction patterns revealed that all prepared samples have hexagonal structures. The scanning electron micrographs revealed the platelet-like structure of the grains, which would help enhance the magnetic permeability of the materials. Magnetic parameters were investigated in the range of applied field ±12.5 kOe. The hysteresis loops revealed the paramagnetic nature of all the synthesised samples. With the substitution of Mg contents, the maximum magnetization increased from 1.05 to 2.62 (emu/g) and the remanence from 0.02-0.09 (emu/g), while the coercivity also increased. The magnetic permeability was determined over the frequency range of 20 Hz to 20 MHz. The magnetic permeability of the synthesized hexagonal ferrites is enhanced due to the presence of grains having a platelet-like structure. Furthermore, the particle size calculated using Langevin equations varied in the range of 4.7 to 6.5 nm. The calculated magnetic permeability properties make this synthesised ferrite material useful for super-high-frequency devices.

Thermodynamic Interpretation of Electron Density and Temperature Description in the Solar Corona

We reach a thermodynamic interpretation of the CODET model and its accurate electron density and temperature prediction, grounded on the physics of hydro magnetism in global equilibrium. The thermodynamic interpretation finds consistency with the model of a magneto-matter medium possessing a 3-D Langmuir structure. That medium is diamagnetic in the context of ideal magnetohydrodynamic (MHD). It is shown that this magneto-matter has unusual characteristics consistent with assuming that the low quiescent solar corona possesses a nature-state, non yet studied. It is further noticed that this is wholly consistent with the CODET model prediction of a polytropic anomalous index for the electron gas of the Sun’s corona. Constitutive properties are derived from this novel state of nature, like magnetic permeability properties and non-dispersive acoustic speed. This non-dispersive acoustic speed is also expected to predict the observed equilibration time for the 1.1 to 1.3R⊙ quiescent corona during the solar minimum from 2008 to 2009.

Detection of Internal Defects of Full-Size Composite Insulators Based on Microwave Technique

In this article, a detection method based on microwave technique is proposed to detect the internal defects of composite insulators. Based on this method, an automatic detection system is developed for full-size composite insulator. In the experiments with 110-kV composite insulators, three types of defects, namely the air-gap defect, carbonization defect, and conductive defect, are artificially made, and they are located exactly by the developed automatic defect detection system. It is found that, due to the dielectric constant and magnetic permeability properties, the conductive defect can be detected easily, whereas the carbonization defect is the most difficult one to be detected among all three defects. In addition, a real defective 500-kV composite insulator from transmission line after years of operation is also detected by the developed system and the results are consistent with the infrared imaging method. According to the test results, the developed system is efficient, labor-saving, and robust. It can have a great potential in the quality control of composite insulators.

Ferric metal-organic framework for microwave absorption

In this study, we have shown for the first time that ferric metal-organic framework (Fe-MOF) has the ability to attenuate gigahertz-range electromagnetic radiation through means of a novel interference mechanism. A large reflection loss value of −54.2 dB can be obtained, equivalent to over 99.999% absorption efficiency. The microwave absorption performance is largely dependent on the dielectric permittivity and magnetic permeability properties. The electrical loss ratio tgδε increases with the frequency from 0.13 at 1.0 GHz to 0.69 at 18.0 GHz, while the magnetic loss ratio tgδμ is only between 0.05 and 0.14. The conductivity σ increases with the frequency from 0.08 S/m at 1.0 GHz to 5.24 S/m at 18.0 GHz, while the skin-depth δ decreases with the frequency. The thickness (d) of the absorber is inversely proportional to the reflection loss peak value (RLpeak), the reflection loss peak frequency (fpeak), and the critical reflection loss peak width (Δf10). The non-zero magnetic susceptibility (χ) accelerates the shift of fpeak to lower values as d grows bigger; however, it improves the RLpeak value and larger microwave absorption efficiency and reduces the quick narrowing of the critical frequency range. The microwave performance of Fe-MOF is likely related to its microwave conductivity, which may originate from the polar rotations in the interface or defects. A new mechanism is proposed for the large reflection loss based on the interference of the reflected microwave from the front and back surface of the microwave absorber, especially when the thickness matches with the odd integer values of the wavelength.

Measurements of Complex Magnetic Permeability of Nano-Size $\varepsilon$-Al$_{\rm x}$Fe$_{2-{\rm x}}$O$_{3}$ Powder Materials at Microwave and Millimeter Wavelengths

The imaginary part of complex magnetic permeability spectrum confirms the strong ferromagnetic resonance absorptions to appear at 89 GHz for the e-AlxFe2-xO3 nanomagnets prepared by sol-gel techniques for the x value to be 0.66. A strong anomalous dispersion corresponding to 89 GHz resonance is also observed in the real part of magnetic permeability spectrum. The free space quasi-optical spectrometer equipped with a set of tunable backward-wave oscillators as power sources is used in this work to study the transmittance, real and imaginary parts of complex dielectric permittivity and real and imaginary parts of complex magnetic permeability properties of this nano magnet materials. Complex dielectric permittivity and Complex magnetic permeability spectra over six waveguide bands are almost flat in the 8-40 GHz range The vector network analyzer and in-waveguide measurements were employed for the measurements over 8-40 GHz range. The absorption property is suggested to be caused by the natural resonance achieved by the large magnetic anisotropies in this series of aluminum substituted ferrite nanomagnets. The absorption peak shifts to the lower frequencies with increasing value of x -parameter. The average particle size of e-AlxFe2-xO3 nanomagnets lies between 25 to 50 nm. The absorption and dispersion characteristics are repeatable for the same density of the powder material.

New advances in three dimensional transient electromagnetic inversion

Inversion of transient electromagnetic (TEM) data sets to image the subsurface three-dimensional (3-D) electrical conductivity and magnetic permeability properties can be done directly in the time domain. The technique, first introduced by Wang et al. (1994) for causal and diffusive electromagnetic fields and subsequently implemented by Zhdanov and Portniaguine (1997) in the framework of iterative migration, is based upon imaging methods originally developed for seismic wavefields (Claerbout, 1971; Tarantola, 1984). In this paper we advance the original derivations of Wang et al. (1994) and Zhdanov and Portniaguine (1997) to treat non-causal TEM fields, as well as correct a flaw in the theory for treatment of magnetic field data. Our 3D imaging scheme is based on a conjugate-gradient search for the minimum of an error functional involving EM measurements governed by Maxwell's equations without displacement currents. Treatment for magnetic field, voltage (time derivative of the magnetic field) and electric field data are given. The functional can be computed by propagating the data errors back into the model in reverse time along with a DC field, sourced by the integrated data errors over the measurement time range. By correlating these fields, including the time-integrated back-propagated fields, with the corresponding incident field and its initial value at each image point, efficient computational forms for the gradients are developed. The forms of the gradients allow for additional efficiencies when voltage and electric field data are inverted. In such instances the combined data errors can be back-propagated jointly, significantly reducing the computation time required to solve the inverse problem. The inversion algorithm is applied to the long offset transient electromagnetic measurement (LOTEM) configuration thereby demonstrating its capability in inverting non-causal field measurements of electric field and voltage, sourced by a grounded wire, over complex structures. Findings also show that migration, without iteration or preconditioning, is not an effective imaging strategy; reconstructions at the first inversion iteration bear little resemblance to simple or complex test models.

Effect of 50 MeV Li 3+ ion irradiation on structural, dielectric and permeability studies of In 3+ substituted Mg–Mn ferrite

The 50 MeV Li 3+ ion irradiation induced modifications on structural, dielectric and magnetic permeability properties of Mg 0.9Mn 0.1In x Fe 2− x O 4 ferrites have been studied. The X-ray diffraction studies show that a compressive strain is produced in the lattice after irradiation and the effect of strain is being observed on the dielectric and magnetic permeability properties. The dielectric constant as a function of frequency for unirradiated samples is well explained by Koop’s model. Whereas, for irradiated samples this is explained by the collective contributions of p and n type carriers. The decrease in dielectric constant of irradiated samples in magnitude is explained on the basis of Maxwell–Wagner interfacial polarization. The electric loss parameter for irradiated sample is increased from that of the unirradiated samples and also show the resonance peak, which is explained by the Maxwell–Wagner interfacial polarization. However, the resonance peaks are not present in unirradiated samples. The dispersion in initial permeability follows the same trend for unirradiated as well as for irradiated samples. A small decrease in permeability is observed for irradiated samples. These results are explained by considering the magneto-mechanical effects generated by stress field induced by the ion irradiation in these samples. The magnetic loss in irradiated samples is drastically reduced due to suppression of imaginary part of permeability.

Spin reorientation in substituted iron garnets investigated by Mössbauer spectrometry

Substituted iron garnets exhibiting very high magnetic permeability properties were investigated by 57Fe Mössbauer spectrometry. The temperature dependences of the hyperfine field and the quadrupole shift at the different iron sites suggest the existence of a distribution of spin reorientation transitions, distribution attributed to the cationic substitution. This phenomenon which is in qualitative agreement with permeability measurements, is attributed to the introduction of scandium and terbium cations in the iron and yttrium sublattices, respectively. The hyperfine data are consistent with a gradual change of the easy magnetization axis from the [100] to [111] directions with increasing temperatures. The cationic distribution resulting from the octahedral and tetrahedral iron site occupancies differs from that encountered in pure iron garnets.