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PhD thesis defense of Grzegorz Jagło

Wpływ uporządkowania magnetycznego na dynamikę sieci wybranych trójskładnikowych dichalkogenków metali przejściowych

First-principles calculations based on the density functional theory (DFT) method have been carried out to study dynamical properties of the ternary layered transition-metal diselenides KNi[2]Se[2] [A1], KCo[2]Se[2] [A2] and TlCo[2]Se[2] [A3]. A detailed analysis of the phonon densities of states, dispersion relation of phonons, and the lattice contribution to the low-temperature heat capacity in KNi[2]Se[2] are provided. Correlations between the magnetic structures of the investigated systems and their lattice dynamics are discussed in detail. A special attention is paid to the behavior of the Raman and infrared-active phonon modes as their frequencies and intensities remain quite sensitive to magnetic interactions. Apart from the dynamical properties, results of the A1, A2, and A3 papers cover a representative set of physical parameters for the AT[2]Se[2] (A = K, Tl; T = Co, Ni) compounds such as optimized atomic positions, lattice constants, and bond lengths. A comparison with the available experimental and theoretical data is given to validate results of the present ab initio calculations. Results of these simulations can be used for interpretation of the phonon spectra measured in the future inelastic neutron scattering, Raman, and infrared experiments. They may also serve as a guide for further experimental and theoretical investigations on AT[2]X[2] (X = S, Te) compounds as well as on more complex systems A[x]T[2-y]X[2-z] which contain lattice defects. They are believed to stimulate design of new experiments on the layered ternary transitionmetal diselenides.