First-principles simulation of ultrathin amorphous carbon films has been performed. Nanohybrid graphene-C60 systems were considered. Total energy calculations were performed using pseudopotential method within density functional theory. Local atomic structure and electronic energy spectrum of the systems were studied. It was demonstrated that fullerene-graphene interaction results in significant deformation of their local atomic structure. Obtained results are in good agreement with experimental X-ray UV spectra of hydrogenated amorphous carbon
Keywords: Phase-change resistive memory, ab-initio simulation, pseudopotential method, Kohn-Sham method, graphene, fullerenes, amorphous carbon, atomic structure, electronic structure, adsorption energy
Biphasic composite materials were synthesized near the La0.7Sr0.3MnO3-based percolation threshold and the second phase, which is an inorganic or organic compound — polyvinyl acetate, paraffin, carboxymethylcellulose, sucrose, and ultrafine silver particles. For composites with an organic matrix, the magnetoresistance values do not exceed 2%, and for composites with silver particles - 8%. The values of isotropic negative magnetoresistance for ceramic samples of 80% LSMO / 20% GeO2 (mass%) reach 13% in a 15 kOu magnetic field with a sensitivity of about 1% / ke in the low-field region. High chemical and radiation stability of these glass composites should be noted. The magnetoresistive properties of such compounds slightly decreased after 60 days of being in water with a salinity of 35 ppm. Composites of 80% LSMO / 20% GeO2 were exposed to X-rays with a dose of 7 Sv from the Co57 source. The magnetoresistive properties and electrical resistance of these composites did not change after that.
Keywords: lanthanum strontium manganite, ceramic two-phase material, one-step synthesis, radiation exposure, magnetoresistance, percolation threshold, dielectric constant, barrier layer, spin-dependent tunneling, spin polarization
The electrical properties of composites based on La0.7Sr0.3MnO3 (LSMO) synthesized at the percolation threshold have been studied: LSMO / Li4P2O7, LSMO / Sb2O3, LSMO / GeO2. The activation energies of these compounds have been determined. New ceramic materials with silver interlayers between LSMO manganite crystallites have been synthesized. The current-voltage characteristics for the LSMO / GeO2 series are given. The nonlinearity of the characteristics is most pronounced for compositions near the percolation threshold, 85% LSMO / 15GeO2.
Keywords: lanthanum strontium manganite, composite material, ceramics, one-step synthesis, magnetoresistance, percolation threshold, dielectric constant, barrier layer, tunneling, spin polarization
A new class of materials is proposed that change their dielectric permittivity as a function of the magnetic field strength. Such materials are two-phase composites of composition La0.7Sr0.3MnO3 / I, where I is the isolating phase, Li4P2O7 or GeO2. The ratio of components is close to the percolation threshold: from 10% to 20% by weight. Dielectric properties have been studied in the frequency range of the measuring field from 1 kHz to 1 MHz in magnetic fields from 0 to 15 kOe. Samples have an inductive impedance, their permittivity is negative. In a magnetic field, the permittivity increases in absolute value and at room temperature the values of the magnetodielectric coefficient reach 28%.
Keywords: lanthanum strontium manganite, composite material, ceramics, one-step synthesis, magnetoresistance, percolation threshold, dielectric constant, barrier layer, tunneling, spin polarization
Based on our own, as well as literary experimental data, the analysis of the Influence of a barrier material used to create heterogeneous composites based on La0.7Sr0.3MnO3 on their magnetoresistive properties is carried out. Such composites differ in existence of an isotropic negative magnitorezistivnost (MR) connected from backs - dependent tunneling of carriers in magnetic field. The largest value MR up to 15% in the field of 15 kOe are shown when using glass-like GeO2 oxide at a percolation ratio of components.
Keywords: lanthanum strontium manganite, composite material, ceramics, one-step synthesis, magnetoresistance, percolation threshold, dielectric constant, barrier layer, tunneling, spin polarization
Many complex oxides of transition metals show effect of enormous dielectric permeability. New complex layered oxides LnSr2CuTiO6,5 (Ln = La, Nd, Pr) are synthesized. Their structure by means of x-ray diffraction on the Shimadzu XRD-7000 S is investigated. Processing of XRD was carried out in the program FULLPROF-2013. The main X-ray reflexes are indicated in space group I4/mmm (№ 139). The data of the crystal-chemical analysis which are carried out taking into account a charge state and coordination environment of cations show that distortion of coordination polyhedrons is significantly reduced in series Ln = La→Nd. The unit cell parameters naturally decrease according to reduction of ionic radiuses of La→Nd. Dielectric properties of materials investigated using the universal analyzer of a frequency response Solartron 1260A in the range of frequencies 1mHz - 16МHz with a signal amplitude 500-900 mV. Increasing the dielectric constant is possible due to the charge ordering caused by uneven distribution of charge. Frequency dependences of an imaginary and real part of dielectric constant are given.
Keywords: dielectric constant , complex oxide, transition metal, perovskite, x-ray diffraction, microstructure, crystal-chemical analysis, impedance- spectroscopy, charge ordering, coordination polyhedron