Spin-phonon coupling in antiferromagneticBi2Sr2CoO6+δ: An infrared reflectance study

Abstract

The ab-plane infrared and optical reflectance of single-crystal Bi 2 Sr 2 CoO 6+␦ ͑0.4Ͻ ␦ Ͻ 0.5͒ have been measured over a wide frequency range ͑50-55000 cm −1 ͒ and at temperatures between 20 and 330 K. The room-temperature infrared spectrum displays an insulating characteristic. The optical gap determined from the infrared conductivity ͑ϳ0.53 eV͒ is consistent with thermal activation energy from dc transport measurements. Upon passing through the 265 K antiferromagnetic ordering transition, a softening of the phonon mode near 205 cm −1 correlates well with the temperature-dependent normalized square of the sublattice magnetization. Furthermore, the magnetic-order-induced splitting of the phonon modes at about 238 and 376 cm −1 is observed. Additionally, the phonon mode at about 588 cm −1 exhibits a Fano-type line shape. Since no appreciable structural change was detected at low temperatures in x-ray diffraction studies, all of these observables suggest a complex nature of spin-phonon coupling in this material.

Electronic structure and lattice dynamics of LixCoO2single crystals

“…However, strong hybridization between oxygen 2p and cobalt 3d orbitals leads to the breaking of local symmetry, thereby enabling these transitions [24]. The absorption peaks near 3.35 and 5.20 eV were assigned to charge-transfer transitions from the occupied hybridized oxygen 2p with cobalt 3d states to the unoccupied cobalt 3d states [25,26]. Our results also show great similarity with the local density approximation calculations of Na x CoO 2 [27].…”

“…Since chain-type antiferromagnetic ordering has previously been detected in Li 0.50 CoO 2 at approximately 200 K on the basis of magnetic susceptibility measurements [9], the observed large splitting of the E g mode across the phase transition temperature should be closely related to the coupling between the lattice and spin degrees of freedom. Such phonon splitting behavior near T N is similar to that of infrared-active phonon modes observed in antiferromagnetic transition metal oxides [26,31,32]. We speculate that the doubly degenerate in-plane E g phonons are lifted because of strong spin-phonon interaction.…”

Spin-phonon coupling in Sr and Ti incorporated 9R-BaMnO3

“…Figure 6 (a, b) shows the deviation for the modes P3, P4, P7, P8, Q3, Q4, Q7, and Q8 as a function of temperature. We have estimated the strength of spin-phonon coupling using the relation [34][35][36]:…”

Hybrid density-functional calculations of phonons inLaCoO3

“…The majority of publications discussing the ab initio calculation results for LaCoO 3 are based on the so-called LDA(GGA)+U method, which was shown to reproduce correctly a nonmagnetic behavior of LaCoO 3 at low temperatures [6][7] . A commonly used approach is to find the U-parameter by fitting materials properties to experimental values 8 . The U-values so far discussed in the literature for LaCoO 3 vary in the range between ~3 and ~8 eV depending on the basis and Hamiltonian.…”