Effective Impedance Method for In situ Ellipsometry Analysis of Magnetic Films

The method of effective surface impedance is proposed and applied for in situ characterisation of magnetic structures. For any ellipsometry investigations a proper choice of a physical model is important for solving the inverse problem. Reasonable approximations used for in situ ellipsometry monitoring are assumptions of a constant rate of layer growth and stable optical parameters. Standard ellipsometry analysis requires the model response to be calculated from every layer in the structure. Errors from underlying layers propagate through the entire structure and accumulate. In this case a method of a pseudosubstrate is used which approximates the underlying structure as a single interface (so called virtual interface), rather than tracking the entire sample history. The virtual interface is placed at some level and growth is modelled on this interface with no knowledge retained for the underlying structure. There are various methods for describing the virtual interface. In this paper, the concept of the effective impedance is used which requires only three measurement data points and is convenient for combined investigation of optical and magneto-optical properties. The algorithm is based on the calculation of the characteristic matrix of the layer (Abeles matrix) and surface impedance of the virtual interface using two ellipsometric experimental data points. The method is successfully used to analyse Co / SiCo films. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3358

On Influence of Magnetic Fields and Excitation Conditions on the Magnetization Distribution in Microwire Magnetoimpedance Element

One of important condition for the successful development of effective magnetic field sensors based on amorphous ferromagnetic microwires is to identify factors affecting the reversal processes in the surface layer of the magnetoimpedance wire. In this paper, the distribution of magnetization is considered as a function of the magnetic properties of the wire material, current flowing through it, strength and orient a-tion of the external magnetic field. The impact of these factors on the performance of the sensor is analyzed on the basis of the numerical simulation of the sensor element. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3640

On Properties of Magneto-dielectric Composites in the Effective Medium Approximation

The development of ultra-broadband composite absorbers of electromagnetic waves depends largely on optimal combination of the medium characteristics that determine their absorption capacity and conditions for impedance matching and destructive interference. It is possible to achieve a higher absorption level in a wider frequency band by combining a variety of mechanisms enhancing the loss of electromagnetic field energy, for example, by combining specific constituents in a composite matrix. The analysis of various mix-ing models for constituent parameters is carried out in the effective medium approximation for ferrite-dielectric composites. It appears that the standard mixing rules do not explain the increase in the effective permittivity of ferrite composites in comparison with that of bulk ferrites. The proposed mechanism of such increase is based on the conductive properties of the ferrite granules and the equivalent capacitance effect. The developed model of permittivity calculation is based on the equivalent capacitor circuits and gives a satisfactory agreement with the experimental data. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3640

High Sensitivity Magnetic Sensors Based on Off-diagonal Magnetoimpedance in Amorphous FeCoSiB Wires

The magnetoimpedance (MI) effect has a potential for the development of high performance magnetic sensors. For sensor applications, off-diagonal configuration is preferable when the MI element is excited by ac current and the output is detected from the coil. In the present work, the off-diagonal sensor design was advanced by utilising a complex waveform excitation produced by a microcontroller and applied to a multiple wire MI element. For optimised excitation with a waveform close to a positive half sine form and characteristic frequency of 8 MHz the field resolution of about 60 mV/Oe was achieved. The pulse excitation does not require an additional bias since it includes controllable low frequency components. The concept of microcontroller driven sensor element could be attractive for the development of intellectual sensors. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3358

Effect of Bias Fields on off-Diagonal Magnetoimpedance (MI) Sensor Performance

This paper investigates the performance of off-diagonal magnetoimpedance in Co-based amorphous wire subjected to dc bias fields: circular and orthogonal (with respect to the wire axis). Typically it is as-sumed that the wire impedance is insensitive to the orthogonal field so the wire element can be used to construct 3D sensors. Our results demonstrated the possibility of large impedance change due to this field, in the range of 10 mV/Oe. The dc current in a wire generating a circular field results in improved sensitivi-ty due to elimination of the domain structure and smoothing the effect of the anisotropy deviations. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3633

Magneto-Ellipsometry Investigations of Multilayer Nanofilms of Fe and Co

Spectral ellipsometry technique is demonstrated to be a useful tool for the investigation of optical and magneto-optical parameters of magnetic heterostructures. Ellipsometry parameters ψ, Δ were measured in the range of 350-1000 nm. Solving the inverse problem by a regression method the refractive index and thickness of the layers were deduced. Magneto-optical spectra were detected in the configuration of equatorial Kerr effect which is fully compatible with the ellipsometry measurements. Spectroscopic ellipsometry method of magnetic structure characterisation can be used for in situ monitoring of magnetic film growth in various processes such as magnetron sputtering, electron beam evaporation and ion beam sputtering. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3357

On Properties of Magneto-dielectric Composites in the Effective Medium Approximation

The development of ultra-broadband composite absorbers of electromagnetic waves depends largely on optimal combination of the medium characteristics that determine their absorption capacity and conditions for impedance matching and destructive interference. It is possible to achieve a higher absorption level in a wider frequency band by combining a variety of mechanisms enhancing the loss of electromagnetic field energy, for example, by combining specific constituents in a composite matrix. The analysis of various mix-ing models for constituent parameters is carried out in the effective medium approximation for ferrite-dielectric composites. It appears that the standard mixing rules do not explain the increase in the effective permittivity of ferrite composites in comparison with that of bulk ferrites. The proposed mechanism of such increase is based on the conductive properties of the ferrite granules and the equivalent capacitance effect. The developed model of permittivity calculation is based on the equivalent capacitor circuits and gives a satisfactory agreement with the experimental data. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3640

Laser processing effect on magnetic properties of amorphous wires

A study was conducted to observe the laser processing effects on the magnetic properties of amorphous wires. Weekly interacting heterogeneous structures with different magnetic properties were formed by the local annealing by argon laser. Favourable changes were observed due to the creation of local stresses and structural interfaces

Electromagnetic-field quantization and spontaneous decay in left-handed media

We present a quantization scheme for the electromagnetic field interacting with atomic systems in the presence of dispersing and absorbing magnetodielectric media, including left-handed material having negative real part of the refractive index. The theory is applied to the spontaneous decay of a two-level atom at the center of a spherical free-space cavity surrounded by magnetodielectric matter of overlapping band-gap zones. Results for both big and small cavities are presented, and the problem of local-field corrections within the real-cavity model is addressed.Comment: 15 pages, 5 figures, RevTe