We report on the lattice and spin dynamics in monopnictide CrAs using polarized Raman scattering. This system exhibits a first-order magnetostructural phase transition at $T_N\sim 265\mathrm{K}$, below which the magnetic moments of Cr form an incommensurate double helical magnetic structure while the unit-cell volume abruptly expands. Across the transition, the frequencies of the fully symmetric $A_g$ phonons strongly renormalize, which along with the results of first-principles calculations suggests the presence of a sizeable coupling of the phonons to the magnetic degrees of freedom in this compound. In addition, we observe two broad modes at around 350 and $1700\mathrm{c}{\mathrm{m}}^{-1}$ in the magnetic phase, which we associate with two-magnon Raman scattering. This work provides one of the few examples of magnetic Raman scattering from a noncollinear magnet.

• Received 3 May 2019
• Revised 15 July 2019

DOI:https://doi.org/10.1103/PhysRevB.100.104301