Raman scattering study of lattice and magnetic excitations in CrAs

TL;DR

This study investigates the lattice and magnetic excitations in CrAs using polarized Raman scattering, revealing strong phonon renormalization and two-magnon modes associated with its complex magnetic phase transition.

Contribution

It provides new insights into phonon-magnetic coupling and magnetic excitations in CrAs, a non-collinear magnet, through detailed Raman scattering analysis.

Findings

Phonon frequencies strongly renormalize across the magnetic transition.

Observation of two broad two-magnon Raman modes at 350 and 1700 cm-1.

Evidence of significant phonon-magnetic coupling in CrAs.

Abstract

We report on the lattice and spin dynamics in the monopnictide CrAs using polarized Raman scattering. This system exhibits a first-order magneto-structural phase transition at T_N~ 265 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 Ag phonons strongly renormalize, which along with the results of first-principle calculations suggest 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 around 350 and 1700 cm-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 non-collinear magnet.