Solid State Phenomena Vols. 168-169

Abstract: The properties of Co-SiO2 nanogranular composite films, containing a Co volume fraction ranging from 0.3 to 0.8, have been characterized by means of magnetic measurements, NMR study, and ferromagnetic resonance. Thermal decrease of CoX(SiO2)100-X magnetization follows the T3/2 law and allows to estimate the exchange interaction constant A. With growing nominal Co content the transitions from granular to continuous structural state at 36% Co are registered by FMR measurements. The spectrum of standing spin-wave has been detected in the perpendicular experiment configuration for films with the Co content above 52 vol. %. It is found that the type of the dispersion relation of spin waves in Co-SiO2 composite films is affected by the exchange coupling fluctuations.

Abstract: The ground state magnetization of nanowires built of ferromagnetic crystallites is considered taking into account the magnetostatic interaction. The criterion of formation of domains is found. The thickness of a domain wall is calculated analytically and the results are compared with the numerical simulations. We show that when the exchange coupling between crystallites is absent its role is played by magnetostatics that ensures the existence of stable domain structure. The direction of the induced anisotropy axis is shown to be determined by the shape of crystallites.

Abstract: The interlayer coupling in Co/Ge/Co trilayer films has been experimentally studied by the SQUID magnetometry and electron magnetic resonance. It has been found that the interlayer coupling is temperature-dependent. The values of the exchange constants have been determined.

Abstract: Determination of stable phases formed at the Fe/Si interface in (Fe/Si)n structure, grown by thermal evaporation in an ultrahigh vacuum system was performed using conversion electron Mössbauer spectroscopy (CEMS).

Abstract: Structure and magnetic properties of nanoscale [Gd/Ti]n multilayers prepared by rf-sputtering are studied. It is found that the decrease in the Gd layer thickness LGd leads to beginning of the structure transformation in Gd layers from the fine-crystalline to amorphous state when LGd becomes less than 2 nm. The Curie temperature TC decreases as a function of the Gd layer thickness in the same way as in early studied epitaxially grown Gd films, i.e. in case for which the finite-size effect plays most important role. A deviation of the TC(LGd) behaviour at very low LGd from the fit according to the finite-size law is probably caused by the island-like structure of the Gd layers.

Abstract: Features of the optical properties of nanostructured samples of cupric oxide CuO prepared by shock wave loading (SWL) and by high pressure torsion (HPT) methods have been investigated by means of spectroscopic ellipsometry in the range of 0.5-5.0 eV. The results for nanostructured samples are discussed in comparison with the measurement data of the CuO single crystal. Dispersion of the components of the complex permittivity in nanostructured CuO samples is significantly different from that for the single crystal. The optical spectral density of the nanostructured CuO is redistributed from the energy region above the fundamental absorption edge to the region below the edge. The shift is unexpected strong for samples prepared by the HPT method. The intensity of the optical spectra is suppressed in the range above the fundamental absorption edge and increases in low-energy one. It has been shown that the energy positions of the main electronic transitions in nanostructured samples on the whole are the same as in the single crystal; at the same time, intensity of the low-energy transitions increases. The possible causes of this increase and resolution of the fine absorption structure of the nanostructured CuO are discussed.

Abstract: Magnetic properties of iron-containing coatings obtained on aluminum by plasma electrolytic oxidation were analyzed in this paper. Theoretical curves of demagnetization of these objects are obtained. It is shown that the magnetic states of the analyzed samples can be caused by the presence of several phases with very different magnetic properties.

Abstract: The magnetoimpedance (MI) in thin films and magnetic multilayers has been extensively studied in recent years. One of the important problems which is still under discussion is the temperature dependence of MI of the multilayered nanostructures for temperatures up to 200 oC. In this work magnetic properties and temperature dependence of the magnetoimpedance of Fe19Ni81/Cu/Fe19Ni81 multilayers with opened and closed magnetic pathes were studied and comparatively analyzed for the functional temperature interval of + 23 oC to + 160 oC.

Abstract: Within an sd-model involving a spin-fluctuation method, the behavior of strong-paramagnetic semiconductor FeSi in strong electrical field is numerically investigated. It is established that due to the self-heat phenomenon there exists a bi-stable state, and the (I-U)-characteristic is S-like in shape. It is shown that in the bistable area there arise current self-oscillations at a constant voltage.

Abstract: Complementary analysis of morphology, crystal structure, electronic transport, and magnetic properties is applied to optimize the epitaxial growth of Fe(001) films with the improved electronic transport and magnetic properties. It was found that the mean free path of residual electrons and coercive forces are correlated in the epitaxial single-crystal Fe(001) films grown under different temperatures and depend on the film morphology.