Raman scattering spectroscopic observation of a ferroelastic crossover in bond-frustrated PrCd$_3$P$_3$

TL;DR

This study uses Raman spectroscopy to reveal a structural instability in PrCd$_3$P$_3$, a layered material with potential for controlling magnetic states via strain-induced ferroelectricity in the non-magnetic layers.

Contribution

It uncovers a phonon soft mode and structural instability in the CdP layers of PrCd$_3$P$_3$, linking lattice dynamics to electronic and magnetic properties.

Findings

Detection of a soft phonon mode indicating structural instability

Confirmation of a singlet ground state for Pr$^{3+}$ ions

Splitting of crystal electric field levels due to lattice distortion

Abstract

2D magnetism in triangular lattices has already shown potential for hosting exotic magnetic states. Control of these magnetic states, both in terms of magnetic properties and in terms of charge doping would be the next step. This makes materials which combine triangular lattice magnetic layers with layers hosting interesting structural or electronic properties particularly useful. PrCd$_3$P$_3$, studied in this work, is one of a family of materials where triangular lattice layers of magnetic rare earth ions alternate with semiconducting hexagonal CdP layers. Using Raman scattering spectroscopy we uncover a structural instability in the CdP layers, associated with a soft mode behavior of a phonon in these layers. Raman scattering detects crystal electric field excitations, and confirms a singlet ground state for Pr$^{3+}$ and splitting of the doublet levels as a result of the structural instability in CdP layers. While Pr$^{3+}$ is non-magnetic in PrCd$_3$P$_3$ we speculate that this family of materials can realize control of the magnetic layer through the CdP layer which can become ferroelectric under strain that would relieve frustration.