Evidence for local lattice distortions in giant magnetocapacitive CdCr2S4

TL;DR

This study reveals local lattice distortions in CdCr2S4 linked to giant magnetocapacitive effects, showing anomalies in phonon modes and symmetry changes below certain temperatures, indicating multiferroic behavior.

Contribution

It provides experimental evidence of lattice distortions and symmetry loss in CdCr2S4 associated with its magnetocapacitive properties, highlighting the role of hybridization and polar modes.

Findings

Anomalies in optical phonon modes at T*=130 K

Loss of inversion symmetry below T_c=84 K

Photo doping restores symmetry

Abstract

Raman scattering experiments on CdCr2S4 single crystals show pronounced anomalies in intensity and frequency of optical phonon modes with an onset temperature T*=130 K that coincides with the regime of giant magnetocapacitive effects. A loss of inversion symmetry and Cr off-centering are deduced from the observation of longitudinal optical and formerly infrared active modes for T<T_c=84 K. The intensity anomalies are attributed to the enhanced electronic polarizability of displacements that modulate the Cr-S distance and respective hybridization. Photo doping leads to an annihilation of the symmetry reduction. Our scenario of multiferroic effects is based on the near degeneracy of polar and nonpolar modes and the additional low energy scale due to hybridization.