Cupric oxide as induced-multiferroic with high-TC

Materials that combine coupled electric and magnetic dipole order are termed "magnetoelectric multiferroics"1-4. In the past few years, a new class of such materials, "induced-multiferroics", have been discovered5,6, wherein non-collinear spiral magnetic order breaks inversion symmetry, thus inducing ferroelectricity7-9. Spiral magnetic order often arises from the existence of competing magnetic interactions that reduce the ordering temperature of a more conventional collinear phase10. Hence, spiral-phase-induced ferroelectricity tends to exist only at temperatures lower than ~40 K. Here we propose that copper(II) oxides (containing Cu2+ ions) having large magnetic superexchange interactions11 can be good candidates for induced-multiferroics with high Curie temperature (TC). In fact, we demonstrate ferroelectricity with TC =230 K in cupric oxide, CuO (tenorite), which is known as a starting material for the synthesis of high-Tc (critical temperature) superconductors. Our result provides a new paradigm in the search for high-TC magnetoelectric multiferroics, in a class of materials that has also produced high-Tc superconductivity.