Giant pressure-enhancement of multiferroicity in CuBr2

TL;DR

This study demonstrates a significant pressure-induced increase in the multiferroic critical temperature of CuBr2, reaching 162 K at 4.5 GPa, which is the highest for a non-oxide type-II multiferroic, with implications for high-temperature applications.

Contribution

The paper reports the discovery of giant pressure-enhancement of multiferroicity in CuBr2, including structural analysis and first-principles calculations explaining the mechanism.

Findings

Critical temperature increased from 73.5 K to 162 K at 4.5 GPa.

Dielectric loss remains small under high pressure.

Pressure enhances magnetic interactions between CuBr2 chains.

Abstract

Type-II multiferroic materials, in which ferroelectric polarization is induced by inversion non-symmetric magnetic order, promise new and highly efficient multifunctional applications based on the mutual control of magnetic and electric properties. Although this phenomenon has to date been limited to low temperatures, here we report a giant pressure-dependence of the multiferroic critical temperature in CuBr$_2$. At 4.5 GPa, $T_\mathrm{C}$ is enhanced from 73.5 to 162 K, to our knowledge the highest value yet reported for a non-oxide type-II multiferroic. This growth shows no sign of saturating and the dielectric loss remains small under these high pressures. We establish the structure under pressure and demonstrate a 60\% increase in the two-magnon Raman energy scale up to 3.6 GPa. First-principles structural and magnetic energy calculations provide a quantitative explanation in terms of dramatically pressure-enhanced interactions between CuBr$_2$ chains. These large, pressure-tuned magnetic interactions motivate structural control in cuprous halides as a route to applied high-temperature multiferroicity.