We report results of the Raman measurements for ${\mathrm{SrRu}}_2{\mathrm{O}}_6$ having extraordinary high Néel temperature for a layered material. No additional phonon modes were detected at the temperature of magnetic transition thus excluding lowering of the symmetry in the magnetically ordered phase. An unusual increase in softening and damping of some phonons as the temperature approaches $T_N$ indicates the appearance of a continuum of interacting electronic excitations at $T\ge 300\text{K}$. We also observe an intensive Raman response at 2050 ${\mathrm{cm}}^{-1}$. Analysis of the polarization dependence and comparison with available theoretical data shows that this peak likely originates from the transitions between molecular orbitals previously proposed to explain the magnetic properties of ${\mathrm{SrRu}}_2{\mathrm{O}}_6$. It can be explained by two magnon excitations only if the magnon bandwidth is $\sim 140$ meV.

• Received 9 September 2018
• Revised 3 December 2018

DOI:https://doi.org/10.1103/PhysRevB.99.085103