Raman spectroscopic evidence for multiferroicity in rare earth nickelate single crystals

I Ardizzone,M Medarde,D G Mazzone,A B Kuzmenko,D Van Der Marel,D J Gawryluk,J Teyssier,I Crassee

doi:10.1103/physrevresearch.3.033007

I Ardizzone, M Medarde + Show 6 more

Open Access

https://doi.org/10.1103/physrevresearch.3.033007

Copy DOI

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.

Highlights

During recent years materials with the perovskite structure have become the subject of intensive research in the field of photovoltaic cells [1], battery engineering [2], and cancer therapy [3]
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
Cooling the samples through the magnetic phase transition has a surprisingly large impact on the Raman spectra, in particular showing a large number of additional modes which we interpret as phonons, with a few exceptions that we will discuss first: For all compounds except ErNiO3 and HoNiO3, we observe an additional mode at the low-frequency end of the spectrum, showing a strong redshift on raising the temperature to TN

Summary

INTRODUCTION

During recent years materials with the perovskite structure have become the subject of intensive research in the field of photovoltaic cells [1], battery engineering [2], and cancer therapy [3]. On entering the insulating phase, a differentiation occurs in the local electronic configuration of the nickel atoms, leading to a modified unit cell containing two pairs of nonequivalent nickel atoms characterized by short and long bonds with the surrounding oxygen atoms [23,24,25,26,27]. This phenomenology is widely agreed on and has been labeled in the literature as, among other things, “bond disproportionation” and “breathing distortion,” the latter of which we employ in this paper. It has been predicted that the combination of breathing distortion and noncentrosymmetric magnetic order can induce a breaking of the inversion symmetry in the crystal lattice and induces an electric dipole, making them type-II multiferroics. [36,37,38,39,40,41,42,43,44,45]

RESULTS

DISCUSSION

KEY IMPLICATIONS OF THE EXPERIMENTS