Solid State Phenomena Vols. 168-169

Abstract: The effect of Cr-buffer-layer thickness on the structure, giant magnetoresistance, and coercivity of DC sputtered Cr(tCr)/[Co90Fe10(15Å)/Cu(23Å)]8/Cr(10Å) superlattices has been investigated. A drastic change of hysteresis in a short interval of the buffer layer thickness (15 ÷ 20 Å) has been revealed. It has been shown that in superlattices with low coercivity the (111) texture is present, whereas superlattices without texture demonstrate a large coercivity and high GMR ratio.

Abstract: A new method for studying multilayer structure using angle resolved XAFS measurements is proposed. The integral equation describing the relation between the fluorescence intensity for selective spectrum, the incident beam energy, the incident angle and a selective concentration profile, depth-dependent EXAFS has been derived. This integral Fredholm equation of the first kind belongs to the class of ill-posed problems and for the solution it needs special methods. We use the regularization Tikhonov method. The effectiveness of the proposed method was tested using the numerical simulations for trilayer system Cr-Fe-Cr. Some first experimental results for the thin films of pure Cr are also presented.

Abstract: The heterostructure ferromagnetic/semiconductor ZnSiAs2/Si was obtained by using the Si-ZnAs2 phase diagram. The magnetic properties of Zn1-XMnXSiAs2 bulk crystals and ferromagnetic layered heterostructures were similar. The same method was used for preparing a ferromagnetic layer ZnGeAs2 on a germanium substrate.

Abstract: Features of the optical properties of nanostructured strongly correlated oxides CuO, Y3Fe5O12, and FeBO3 in a wide range of energies, which includes both the fundamental absorption region, low-energy electron excitations, and phonon modes have been investigated by methods of optical spectroscopy. Absorption and reflection spectra, Raman spectra, and ellipsometry measurements are carried out on the samples of oxide nanostructured ceramics. High-density nanoceramics were prepared by shock-wave loading and high pressure torsion methods from coarse-grain oxide powders. Strong smearing of the fundamental absorption edge is revealed for all nanoceramics. Anomalous red shift of the absorption edge Eg is found in CuO nanooxide. The features of the optical functions in nanooxides of 3d-metals may be attributed to high defectiveness of nanooxides, peculiarities in the electronic structure of strongly correlated oxides and their tendency to electronic phase separation.

Abstract: In present paper the magnetization of magnetic film consisting of two soft magnetic layers separated by a nonmagnetic interlayer is considered. The film is applied to stiff magnetic substrate. To obtain boundary conditions at the boundary between soft magnetic layers we introduce effective constant of interlayer interaction.

Abstract: The research method for the investigation of magnetic states of single nanoparticles, 1D arrays, 2D, and quasi-2D arrays is used. The possibility of the nanodots magnetic states reconstruction by the space distribution of gradient dipole-dipole interaction force is theoretically justified. The comparison is made between the results of nanoarchitecture numerical simulation in an external magnetic field and experimental data.

Abstract: Two types of magnetoresistive effects can be observed in the multilayer structure of the ferromagnet/polydiphenylenephthalide/non-magnetic metal. One can see the effect of resistance switching in an external magnetic field and also the angular magnetoresistive dependence. The similarities and differences of these effects and other known magnetoresistive effects are considered. The conclusion is drawn that the peculiarities of the magnetoresistance in the ferromagnetic-polymer system are formed in the ferromagnet-polymer interface and the special features of charge injection into the conductive nanoscale channels of the polymer film have the determinative importance.

Abstract: NiCuZn ferrites were prepared by the sol-gel self-combustion method. Nanosized, homogeneous and highly reactive powders were obtained at relatively low temperatures. In present work the variations of structural, magnetic, and microwave properties of NiCuZn ferrite nanoparticles were studied as a function of the annealing temperature. The analysis of XRD patterns showed that only the spinel phase is present. Cell parameters slightly vary with thermal treatment while a crystalline size increases. Magnetic nanoparticles were mixed with an epoxy resin for reflectivity studies with a microwave vector network analyzer using the microwave-guide method in the range of 7.5 to 13.5GHz. Static saturation magnetization value (measured by SQUID) and microwave absorption show clear dependence on the annealing temperature/particle size and the absorption maximum moves towards the higher frequencies with an increase in the average size of the particles.

Abstract: Structure and magnetic properties of nickel oxide (NiO) nanopowders have been studied by X-ray/neutron diffraction, SQUID magnetometer, and micro-Raman spectroscopy. Our diffraction data indicate that at room temperature all NiO powders are antiferromagnetically ordered and have a rhombohedral (R-3m) phase. The SQUID magnetometry and Raman spectroscopy measurements support the presence of the antiferromagnetic ordering.

Abstract: The structure and microwave properties of composites consisting of paraffin as a dielectric host matrix and Fe particles as inclusions have been studied. The composites were prepared by the mechanochemical synthesis and contain 7.7% vol. concentration of the inclusions. The microwave properties were studied in 0.1 to 6 GHz frequency range. The microwave properties of the composites are shown to depend mostly on the size and shape of the inclusions, with the phase composition of the inclusions exerting only a slight effect. With decreasing the inclusions size, the low-frequency peak (300−400 MHz) attributed to the domain wall motion diminishes.