Impedance spectra of thin permalloy films with a nanoisland structure

The behavior of the impedance spectra of island permalloy films prepared through vacuum evaporation onto optically polished glass-ceramic substrates has been investigated in the frequency range from 0.0001 to 100 MHz. A resistor-capacitor model of the films has been developed and the model parameters, for which there is a good agreement with experimental data on the frequency dependences of the real and imaginary components of the impedance, have been determined. The specific features in the behavior of the electrical and physical characteristics with variations in the thickness of the sample and the gap between the measuring electrodes have been investigated. It has been found that the relative permittivity of the films under investigation reaches values ɛ ∼ 10⁷–10⁸. The structural relaxation times have been calculated.     

Dielectric anisotropy of 5CB liquid crystal in a decimeter wavelength range

Parallel and perpendicular components of the dielectric constant for 5CB nematic liquid crystal are measured in a relaxation region. Two frequencies f ₁≈30 and f ₂≈350 MHz are determined at which the inversion of the dielectric anisotropy sign is observed. It is shown that the observed sizable high-frequency shift of f ₂ with respect to the value calculated according the Debye theory is caused by the dielectric resonance near the relaxation region.     

Reduction and noncommutative integration of linear differential equations

A new method is proposed for derivation of exactly integrable linear differential equations based on the theory of noncommutative integration. The equations are obtained by reduction from original equations which are integrable in the noncommutative sense, with a large number of independent variables. It is shown that the reduced equations cannot be solved by traditional methods, since they do not possess the required algebraic symmetry.V. V. Kuibyshev Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 55–60, November, 1993.     

Distribution function of relaxation times for a 4-<Emphasis Type="Italic">n</Emphasis>-pentyl-4′-cyanobiphenyl liquid crystal

The distribution function of relaxation times is reconstructed from the dielectric loss spectrum measured over a wide range of frequencies for a 4-n-pentyl-4′-cyanobiphenyl (5CB) liquid crystal. It is demonstrated that the distribution function for the isotropic and nematic phases is asymmetric in shape. Comparison shows that the reconstructed distribution function is in qualitative agreement with similar functions that are analytically derived from the Cole-Davidson and Havriliak-Negami empirical equations. The specific features observed in the behavior of the distribution function with a variation in the angle between the direction of polarization of a microwave electric field and the director of the liquid-crystal molecules are analyzed. A complex dependence of the permittivity for the liquid crystal in the range of ultrahigh frequencies is explained in terms of additional relaxation mechanisms associated with different motions of molecular fragments of alkyl chains.     

Temperature dependence of the dielectric characteristics of a 5CB liquid crystal within the relaxation region

The temperature dependence of the real part of the permittivity of a 4-n-pentyl-4-cyanobiphenyl liquid crystal was studied within a broad frequency range of 30–5000 MHz and in the temperature interval 20–60°C in the vicinity of the nematic-isotropic-liquid phase transition. It was established that the dispersion of the longitudinal component of the permittivity can be fitted well by a sum of two Debye terms with strongly differing relaxation times. The temperature and frequency dependence of the shorter relaxation time was determined for which the best fit between calculations and experiment was achieved.     

Magnetic structural properties in Alnico alloys under equilibrium conditions and under magnetization

Magnetic structure is studied as a function of the orientation of the easy magnetic axis with respect to ac (4 Hz) and dc magnetizing fields in specimens with various coercivities. Alternating boundary polarity was observed, and a system of magnetization distribution in the equilibrium state is given. Domain width in equilibrium states is measured for various angles of the demagnetizing field. Upon magnetization at various angles, various structural change processes were observed, which have been conditionally divided into four distinct types.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 68–73, August, 1975.     

Loss due to magnetic-rotation hysteresis in bismuth calcium vanadium iron garnet

The field and temperature dependences of the loss due to magnetic-rotation hysteresis have been determined by the rotational-moment method in a (Bi_0.32Ca_2.68Fe_3.66V_1.34O₁₂) single crystal. In the temperature range between –183 and +25 °C, the loss increases with increasing field, reaching a maximum at 2500–6000 Oe; then it decreases, vanishing completely in high fields. The loss behavior can be described well at all temperatures studied by an exponential dependence on the field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 12, No. 2, pp. 65–69, February, 1969.     

Magnetic aftereffects and the barkhausen effect in a magnesium manganese ferrite single crystal

The temperature dependence of the critical magnetic field [H₀(T)] of a magnesium manganese ferrite single crystal is analyzed, together with the changes taking place in the critical magnetic field with time, H₀(t), the temperature dependence of the domain-boundary stabilization field H_st(T), and the time required to establish the equilibrium state of the domain boundaries; the domain structure is examined, and the induced anisotropy constant is calculated; so is the activation energy of the process leading to the stabilization of the domain boundaries. The magnetic aftereffects and the Barkhausen jumps accompanying them are of a diffusion nature.