Lattice dynamics of a quasi-2D layered TlCo2Se2 with a helical magnetic structure

The vibrational properties of a quasi-two-dimensional layered TlCo2Se2 compound exhibiting a helical magnetic order were investigated using density functional theory and an approximation of the harmonic phonons. The helical magnetic structure of this ternary dichalcogenide was shown to be stabilized by phonons. The dynamical properties of the TlCo2Se2 lattice conform with the quasi-2D layered structure of this compound. The intensities of the Raman and infrared active phonon modes of TlCo2Se2 remained sensitive to magnetic interactions, suggesting a rather strong spin-phonon coupling within the Co-Se layers. A detailed analysis of the calculated phonon, Raman and infrared absorption spectra of TlCo2Se2 which was carried out with respect to the spectra of its ferromagnetic (KCo2Se2) and paramagnetic (KNi2Se2) counterparts enabled the essential differences between the dynamical properties of the quasi-2D layered transition-metal dichalcogenides to be elucidated.