Investigation of spin-phonon coupling in triangular-lattice antiferromagnet AgCrS2 by infrared transmission spectroscopy

In this work, we have investigated the spin-phonon coupling in the triangular-lattice antiferromagnet AgCrS2 by means of infrared transmission spectroscopy. At 300 K, four IR active phonon modes having the typical profile expected for an insulating material have been observed. These phonon modes are found to continuously harden upon cooling due to the slight shrinkage of the lattice. The splitting of a phonon mode and the occurrence of two new phonon modes are observed at TN, providing evidences for strong spin-phonon coupling. It is noted that phonon eigenfrequencies show significant deviations from the anharmonic contribution at temperatures much higher than TN, which is clearly determined by the strong spin fluctuations. Our results suggest that spin-phonon coupling has strong influence even in PM state in this material.