Cupric oxide as an induced-multiferroic with high-TC.

Materials that combine coupled electric and magnetic dipole order are termed 'magnetoelectric multiferroics'. In the past few years, a new class of such materials, 'induced-multiferroics', has been discovered, wherein non-collinear spiral magnetic order breaks inversion symmetry, thus inducing ferroelectricity. Spiral magnetic order often arises from the existence of competing magnetic interactions that reduce the ordering temperature of a more conventional collinear phase. Hence, spiral-phase-induced ferroelectricity tends to exist only at temperatures lower than approximately 40 K. Here, we propose that copper(II) oxides (containing Cu2+ ions) having large magnetic superexchange interactions can be good candidates for induced-multiferroics with high Curie temperature (T(C)). In fact, we demonstrate ferroelectricity with T(C)=230 K in cupric oxide, CuO (tenorite), which is known as a starting material for the synthesis of high-T(c) (critical temperature) superconductors. Our result provides an important contribution to the search for high-temperature magnetoelectric multiferroics.