Glamazda O. Low-dimensional multifunctional crystalline materials: the influence of structural features on the interaction between phonon, electron and magnetic subsystems

The thesis is dedicated to establishing the relationship between the structural features of multifunctional low-dimensional materials and their impact on the phonon, electronic and magnetic subsystems. To achieve the goal of the work a complex experimental-computational approach was used, that combined different spectral techniques and the calculation of the dynamics of the crystal lattice. It was shown for the first time that the luminescence spectra of fullerene films can serve as a qualitative indicator of the appearance of the polymerization. It is shown that fullerene films sprayed on the porous polymer substrates demonstrate the selectivity to some gases due to the creation of a composite structure between fullerene film and polymer substrate. The influence of the environment (pH and temperature) on the spectral properties of SWNT: DNA nanohybrids was studied and their significant stability was shown. It is shown that the adsorbed enzymes on the surface of the obtained nanohybrids do not lose enzyme activity. It is shown that SWNT:poly(C) nanohybrids can form a spatial net with the addition of a porphyrin derivative - cationic tetra-(N-methyl-4-pyridyl)porphyrin (TMPyP4) by promoting exciton energy transfer between nanotubes. The energy transfer rate between adjacent nanotubes was estimated to be about 0.6*1010 s-1. For the first time, the angular dependence of the polarization Raman spectra of a stretched gelatin film with SWNT:DNA nanohybrids was experimentally established and the polarization analysis of the G+ band was performed. The bolometric characteristics of the films of ordered SWNT in a polystyrene matrix were investigated and it was shown that the ordering of SWNT sharply increases the value of the temperature coefficient of electrical resistance in relation to the isotropic arrangement of nanotubes and voltage sensitivity up to 500 VW-1. It was found that the introduction of alloying impurities Rux (x=0-0.2) into the layered antiferromagnet Sr2Ir1-xRuxO4 leads to a rapid weakening of magnetic and lattice excitations, which indicates a close connection between magnetic, structural and electronic subsystems. Anomalies in the vibrational spectra of brownmillerites SrCoO2.5 and SrFeO2.5 due to structural and electronic instability of tetrahedral chains have been revealed. Our study emphasizes the key role of one-dimensional tetrahedral chains in determining the structural and electronic properties of brownmillerites. For the first time, polarized Raman spectroscopy was used to invent the coexistence of a set of competing soft modes with different symmetries in a hybrid Ca3Mn2O7 ferroelectric near the phase transition from the paraelectric to ferroelectric phase. Raman spectroscopy revealed the fractionalization of spin excitations in two-dimensional (α-RuCl3) and three-dimensional (β- and γ-Li2IrO3) Kitaev materials and showed the possibility of separating fermionic and magnon excitations.