Open Access

Jin-Shan Zhang, Yiqi Xie, Xiaoqiang Liu, Aleksandar Razpopov, Vladislav Borisov, Cong Wang, Jianping Sun, Yi Cui, J. C. Wang, Xiao Ren, Hongshan Deng, Xia Yin, Yang Ding, Yuan Li, Jinguang Cheng, Ji Feng, Roser Valentí, Bruce Normand, Weiqiang Yu

• 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 mutual control of magnetic and electric properties. However, to date this phenomenon is limited to low temperatures. Here we report giant pressure-dependence of the multiferroic critical temperature in CuBr2: at 4.5 GPa it is enhanced from 73.5 to 162 K, to our knowledge the highest TC ever reported for non-oxide type-II multiferroics. 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 CuBr2 chains. These large, pressure-tuned magnetic interactions motivate structural control in cuprous halides as a route to applied high-temperature multiferroicity.