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Letter

Nature Materials 7, 291 - 294 (2008)
Published online: 24 February 2008 | doi:10.1038/nmat2125

Subject Categories: Ceramics | Electronic materials | Magnetic materials

Cupric oxide as an induced-multiferroic with high-TC

T. Kimura1, Y. Sekio1, H. Nakamura1, T. Siegrist2 & A. P. Ramirez2

Materials that combine coupled electric and magnetic dipole order are termed 'magnetoelectric multiferroics'1, 2, 3, 4. In the past few years, a new class of such materials, 'induced-multiferroics', has been discovered5, 6, wherein non-collinear spiral magnetic order breaks inversion symmetry, thus inducing ferroelectricity7, 8, 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 approx40 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 an important contribution to the search for high-temperature magnetoelectric multiferroics.