Long-term variations in the critical frequency of the midlatitude F2 layer at noon

Based on an analysis of the midday data of the midlatitude ionospheric stations in the Northern Hemisphere, it is indicated that the quiet monthly median f0F2m depends also on the relative sunspot number R×averaged for 11 years: an increase in R×results in decreasing f0F2m two years later. This dependence is shown to be the main cause of long-term f0F2 variations at all longitudes. On this basis, it is assumed that long-term variations in the solar UV radiation flux and (or) in the thermospheric parameters should depend on R. It is indicated that a linear time variation (trend) of the relative f0F2 values is a less important cause of the longterm variations in f0F2. This ionospheric trend is found to be longitude-dependent: it is significant and maximal at longitudes of 100°-290° E and virtually absent over Europe. This effect is apparently associated with the fact that the ionospheric trend is the sum of trends caused by the greenhouse effect P and the secular variations in the magnetic field M. The trends in P and M are shown to be insignificant, but their sum results in a significant trend at certain longitudes. Copyright © 2001 by MAIK "Nauka/Interperiodica"

Properties of the F2-layer critical frequency median in the nocturnal subauroral ionosphere during low and moderate solar activity

© 2016, Pleiades Publishing, Ltd.Based on an analysis of data from the European ionospheric stations at subauroral latitudes, it has been found that the main ionospheric trough (MIT) is not characteristic for the monthly median of the F2-layer critical frequency (foF2), at least for low and moderate solar activity. In order to explain this effect, the properties of foF2 in the nocturnal subauroral ionosphere have been additionally studied for low geomagnetic activity, when the MIT localization is known quite reliably. It has been found that at low and moderate solar activity during night hours in winter, the foF2 data from ionospheric stations are often absent in the MIT area. For this reason, a model of the foF2 monthly median, which was constructed from the remaining data of these stations, contains no MIT or a very weakly pronounced MIT

Seasonal features in the spread-F probability near midnight over Moscow

Using the data of Moscow station for 1975-1985, the seasonal features in the dependence of the spread-F probability P near midnight on the levels of solar and geomagnetic activity have been analyzed. It has been found that the P dependence on solar activity is most substantial in winter and fall, the P dependence on geomagnetic activity is maximal during equinoxes, and the P dependence on solar activity prevails in summer but is much weaker than in winter and fall. Based on the qualitative analysis of the known mechanisms of the midlatitude spread-F, the regression equation, which shows the P dependence on the solar activity level and thermospheric parameters (temperature and density) at a fixed average level of geomagnetic activity, has been obtained. In this equation the character of the seasonal changes in P is determined by the thermospheric parameters, the relative contribution of which depends on solar activity. The found dependence of the character of the P seasonal variations on the solar activity level has been interpreted based on this equation. © Pleiades Publishing, Ltd. 2009

Longitudinal effect in the dependence of the critical frequency of the midlatitude E layer on solar activity

Variations in the critical frequency of the E layer, foE, measured at Boulder and Tashkent stations located at almost coinciding geographical latitudes but at strongly different geomagnetic latitudes are analyzed. The following conclusions are drawn. (a) Late in the fall and in the winter, the foE values at these stations are distinctly different at low solar activity. This difference decreases with increasing solar activity. In other words, the longitudinal effect in the foE dependence on solar activity is significant for these conditions. (b) This effect is almost absent in summer; i.e., the difference in foE dependence on solar activity at these stations is insignificant for the given season. It has been substantiated that the dependence of the nitric oxide concentration [NO] on geomagnetic latitude, season, and solar activity is one of the main causes of this longitudinal effect. © Pleiades Publishing, Ltd. 2007

Dependence of the long-term variations in the F2-layer critical frequency at midlatitudes on the geomagnetic field

A long-term trend in the F2-layer critical frequency (foF2) has been distinguished based on daytime data of midlatitude stations in the Northern Hemisphere, obtained from 1957 to 1995, and using special measures aimed at eliminating the influence of solar and geomagnetic activities on the ionosphere. It has been obtained that the trend sign and value depend significantly on longitude. The values of the negative trend in foF2 are maximum at the longitudes near the extremal negative declination of the magnetic field. This longitude effect is apparently related to the plasma drift due to the westward thermospheric wind via the long-term wind variations and secular variations in the magnetic field. The increase in the westward wind during 1957-1995 may be related to the time increase in the magnetic disturbance frequency and to a relatively slow wind relaxation to undisturbed state after the end of a magnetic disturbance. © 2002 by MAIK "Nauka/Interperiodica" (Russia)

Magnon bottleneck emergence in La2-xSrxCuO4+δ and its use in studies of the dynamics of CuO2 planes

An improved model of the magnon bottleneck is used to show the possibility of measuring the relaxation rate to a homogeneous magnetization lattice of copper-oxygen planes in copper oxide. The agreement between EPR measurements of the spin dynamical characteristics in CuO2 planes and data obtained by NMR spectroscopy is proven to be adequate. © 1996 American Institute of Physics

Magnetic and superconducting heterostructures in spintronics

This paper is a brief review of investigations, which were carried out during last years by team of magnetic nanostructures and spintronics laboratory, and is dedicated to the 80th anniversary of our Teacher - professor B.I. Kochelaev. © Kazan Federal University (KFU)

Modeling a Superconducting Triplet Spin Valve with Several Layers of a Superconductor

A matrix solution to Usadel linearized equations is used to obtain the critical temperature and distribution of singlet pairing components of a superconductor/ferromagnetic/superconductor/ferromagnetic structure with nonideal boundaries. There is a transition from the π- to the 0-phase state between the superconductor layers upon varying the angle between the magnetizations of ferromagnetic layers in such a structure.</p

Tunneling magnetoresistance in ferromagnetic planar hetero-nanojunctions

We present a theoretical study of the tunneling magnetoresistance (TMR) in nanojunctions between non-identical ferromagnetic metals in the framework of the quasiclassical approach. The lateral size of a dielectric oxide layer, which is considered as a tunneling barrier between the metallic electrodes, is comparable with the mean-free path of electrons. The dependence of the TMR on the bias voltage, physical parameters of the dielectric barrier, and spin polarization of the electrodes is studied. It is demonstrated that a simple enough theory can give high TMR magnitudes of several hundred percent at bias voltages below 0.5 V. A qualitative comparison with the available experimental data is given. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Mean-free path effects in magnetoresistance of ferromagnetic nanocontacts

We investigated the mean-free path effects on the magnetoresistance of ferromagnetic nanocontacts. For most combinations of parameters the magnetoresistance monotonously decreases with increasing the contact cross-section. However, for a certain choice of parameters the calculations show non-monotonous behavior of the magnetoresistance in the region in which the diameter of the contact becomes comparable with the mean-free path of electrons. We attribute this effect to different conduction regimes in the vicinity of the nanocontact: ballistic for electrons of one spin projection, and simultaneously diffusive for the other. Furthermore, at certain combinations of spin asymmetries of the bulk mean-free paths in a heterocontact, the magnetoresistance can be almost constant, or may even grow as the contact diameter increases. Thus, our calculations suggest a way to search for combinations of material parameters, for which high magnetoresistances can be achieved not only at the nanometric size of the contact, but also at much larger cross-sections of nanocontacts which can be easier for fabriaction with current technologies. The trial calculations of the magnetoresistance with material parameters close to those for the Mumetal-Ni heterocontacts agree satisfactorily with the available experimental data. © 2007 EDP Sciences/Società Italiana di Fisica/Springer-Verlag