Raman spectroscopic evidence for multiferroicity in rare earth nickelate single crystals

TL;DR

This study provides Raman spectroscopic evidence of multiferroic behavior in rare earth nickelate single crystals, showing coupled magnetic and ferroelectric order at low temperatures through symmetry-breaking vibrational modes.

Contribution

First experimental Raman data on RNiO3 single crystals confirming multiferroicity and symmetry breaking associated with magnetic ordering.

Findings

Observation of additional vibrational modes below magnetic transition temperature

Evidence of inversion symmetry breaking in the low-temperature phase

Confirmation of multiferroic coupling in RNiO3 single crystals

Abstract

The rare earth nickelates RNiO3 are metallic at high temperatures and insulating and magnetically ordered at low temperatures. The low temperature phase has been predicted to be type II multiferroic, i.e. ferroelectric and magnetic order are coupled and occur simultaneously. Confirmation of those ideas has been inhibited by the absence of experimental data on single crystals. Here we report on Raman spectroscopic data of RNiO3 single crystals (R = Y, Er, Ho, Dy, Sm, Nd) for temperatures between 10 K and 1000 K. Entering the magnetically ordered phase we observe the appearance of a large number of additional vibrational modes, implying a breaking of inversion symmetry expected for multiferroic order.