Wdowik Urszula D, Jagło Grzegorz, Piekarz Przemysław
Institute of Technology, Pedagogical University, ul. Podchorazych 2, 30-084 Cracow, Poland.
J Phys Condens Matter. 2015 Oct 21;27(41):415403. doi: 10.1088/0953-8984/27/41/415403. Epub 2015 Sep 29.
Results of the density functional theory studies of the phonon dynamics in the ternary layered cobalt diselenide are reported. The partial phonon densities of states due to vibrations of K, Co, and Se atoms are analysed in detail. They indicate that phonons associated with the dynamics of Co and Se ions within the [Co2Se2] structural blocks span the entire spectral range extending to 260 cm(-1), whereas phonons from the K-sublattice remain limited to the frequency range of 80-150 cm(-1). The phonons conform with structural features of the quasi-2D layered structure of KCo2Se2. Ferromagnetic order in the Co-sublattice is shown to determine to a great extent the phonon densities of states, the Raman and infrared spectra of KCo2Se2. The in-planar magnetic interactions are responsible for pronounced softening of the high-frequency phonon modes and lead to disappearance of the low-frequency Raman-active mode of the E g symmetry. The observed behavior of the Raman-active and infrared-active modes suggests rather strong spin-phonon coupling in KCo2Se2. Results of the present investigations allow to clarify the origin of substantial differences between dynamical properties of the ferromagnetic Co-based and the paramagnetic Ni-based ternary layered dichalcogenides, both adopting the ThCr2Si2-type structure.
报道了三元层状二硒化钴中声子动力学的密度泛函理论研究结果。详细分析了由于K、Co和Se原子振动引起的部分声子态密度。结果表明，与[Co2Se2]结构块内Co和Se离子动力学相关的声子跨越了延伸至260 cm(-1)的整个光谱范围，而来自K亚晶格的声子仍局限于80 - 150 cm(-1)的频率范围。这些声子与KCo2Se2的准二维层状结构的结构特征相符。结果表明，Co亚晶格中的铁磁序在很大程度上决定了KCo2Se2的声子态密度、拉曼光谱和红外光谱。面内磁相互作用导致高频声子模式明显软化，并导致E g对称的低频拉曼活性模式消失。所观察到的拉曼活性和红外活性模式的行为表明KCo2Se2中存在相当强的自旋 - 声子耦合。本研究结果有助于阐明采用ThCr2Si2型结构的铁磁Co基和顺磁Ni基三元层状二硫属化物动力学性质存在显著差异的原因。
