Small influence of magnetic ordering on lattice dynamics in ${\mathrm{TaFe}}_{1.25}{\mathrm{Te}}_3$

Raman scattering spectra of zigzag spin chain ${\mathrm{TaFe}}_{1.25}{\mathrm{Te}}_3$ single crystal are presented in a temperature range from 80 to 300 K. Nine Raman active modes of $A_g$ and $B_g$ symmetry are clearly observed and assigned by probing different scattering channels, which is confirmed by lattice dynamics calculations. Temperature dependence of the Raman modes linewidth is mainly governed by the lattice anharmonicity. The only deviation from the conventional behavior is observed for $A_g$ symmetry modes in a vicinity of the magnetic phase transition at $T_N\approx 200$ K. This implies that the electron-phonon interaction weakly changes with temperature and magnetic ordering, whereas small changes in the spectra near the critical temperature can be ascribed to spin fluctuations.

Figure 1

(a) Structure of the ${\mathrm{TaFe}}_{1.25}{\mathrm{Te}}_3$ single crystal together with the natural cleavage plane $\left[\overline{1}01\right]$. $\mathbf{x}=1/\sqrt{2}\left(\overline{1}0\overline{1}\right)$ and $\mathbf{y}=\left(010\right)$ correspond to our laboratory system. (b) A view of the ${\mathrm{TaFe}}_{1.25}{\mathrm{Te}}_3$ structure along the $b$ axis. Two neighboring chains of Fe1 spins point in a parallel direction, forming a ferromagnetic zigzag chain, whereas spins of neighboring zigzag chains order antiferromagnetically. One should note that Fe2 is present with occupancy of 0.25.

Figure 2

Polarized Raman scattering spectra of ${\mathrm{TaFe}}_{1.25}{\mathrm{Te}}_3$ single crystal measured at 100 K in various polarizations. The notation in parentheses indicates the polarization directions of the incident and scattered light according to Fig. 1. Inset: surface of the probed ${\mathrm{TaFe}}_{1.25}{\mathrm{Te}}_3$ single crystal.

Figure 3

Unit cell of ${\mathrm{TaFeTe}}_3$ single crystal with the displacement patterns of several $A_g$ and $B_g$ Raman modes. Arrow lengths are proportional to the square root of the interatomic forces.

Figure 4

Temperature dependent Raman scattering spectra of ${\mathrm{TaFe}}_{1.25}{\mathrm{Te}}_3$ single crystal in the $\left(yy\right)$ (left panel) and $\left(xy\right)$ (right panel) polarization.

Figure 5

Temperature dependence of the energy and linewidth for the $B_g^2$ and $B_g^4$ Raman modes of the ${\mathrm{TaFe}}_{1.25}{\mathrm{Te}}_3$ single crystal. The red lines are fitted according to Eq. (2), whereas black lines are guides to the eye.

Figure 6

Energy and linewidth of the $A_g^4,A_g^7$, and $A_g^9$ Raman modes of the ${\mathrm{TaFe}}_{1.25}{\mathrm{Te}}_3$ single crystal as a function of temperature. The red lines are plotted according to Eq. (2), and the black dotted lines are guides to the eye. The insets represent deviations of the Raman mode linewidth from the anharmonic form.