Temperature Dependence of Raman Spectra in Cu2FeSnS4 Magnetic Semiconductor Compound

The temperature dependence of the Raman scattering by phonons performed in bulk polycrystalline Cu2FeSnS4, that crystallizes with tetragonal symmetry in space group P (4) over bar, was measured between 10 and 300 K. The most important decay channel involves the three-phonon process with two phonons of the same branch, including combinations of optical phonons with equal or different frequencies. Additionally, coupling of an optical mode to two phonons of different branches is observed. The strong A-symmetry mode at 325 cm(-1) decays into two optical phonons of the same frequencies (nu) over bar (1) = (nu) over bar (2) approximate to 162 cm(-1). To explain the change of Raman shift with temperature it is necessary to take into account the contribution of thermal expansion contribution. We have observed a soft mode in the Raman spectra which accounts for the antiferromagnetic phase transition that happens in this material at a Neel temperature of about 40 K. The full width at half maximum of this A-symmetry mode, extrapolated to zero temperature, is of about 2.6 cm(-1), when the contribution of intrinsic defect scattering, which is of about 3. cm(-1), is included in the calculation.