Direct Observation of Re-entrant Multiferroic CuO at High Pressures

TL;DR

This study provides experimental evidence of re-entrant multiferroic behavior in CuO at high pressures around 4 GPa, revealing a pressure-induced ferroelectric transition and strong spin-phonon coupling.

Contribution

First detailed experimental investigation demonstrating re-entrant multiferroic phase in CuO under high pressure conditions.

Findings

Ferroelectric transition indicated by dielectric anomalies at 3.4-4 GPa.

Anomalous Raman mode behavior suggests strong spin-phonon coupling.

Magnetic exchange interactions emerge at 3.4 GPa.

Abstract

We have carried out a detailed experimental investigation on CuO using dielectric constant, ac resistance, Raman spectroscopy and X-ray diffraction measurements at high pressures and room temperature. Both dielectric constant and dielectric loss show an anomalous peak in the pressure range 3.4-4 GPa indicating a ferroelectric transition. Raman studies show anomalous behaviour of the Ag mode with a slope change in the mode frequency and a minimum in the mode FWHM at 3.4 GPa indicating a strong spin phonon coupling along [1 0 -1] direction. A step like behaviour in the intensity of the Ag mode is observed at 3.4 GPa, indicating a change in the polarization of the mode. A maximum in the intensity of (2,0,-2)Bragg peak at 3.4 GPa points the occurrence of critical scattering due to emergence of magnetic exchange interaction. All our experimental evidences show to the presence of re-entrant type-II multiferroic behaviour in CuO at about 4 GPa.