Phonon Anomalies Associated with Spin Reorientation in the Kagome Ferromagnet Fe3Sn2

Polarization- and temperature-dependent Raman data along with theoretical simulations are presented for the Kagome ferromagnet Fe3Sn2. Eight out of nine expected phonon modes are identified. The experimental energies compare well with those from the simulations. The analysis of the line widths indicates relatively strong phonon-phonon coupling in the range 0.1-1. The temperature-dependent frequencies of three A1g modes show weak anomalies at approximate to 100 K. In contrast, the linewidths of all phonon modes follow the conventional exponential broadening up to room temperature except for the softest A1g mode, whose width exhibits a kink close to 100 K and becomes nearly constant for T>100 K. These features are indicative of a spin reorientation taking place in the temperature range above 100 K, which might arise from spin-phonon coupling. The low-energy part of the electronic continuum in Eg symmetry depends strongly on temperature. The possible reasons include particle-hole excitation tracking the resistivity, a spin-dependent gap, or spin fluctuations.