title: High-T(c) ferroelectricity emerging from magnetic degeneracy in cupric oxide.
abstract: Cupric oxide is multiferroic at unusually high temperatures. From density functional calculations we find that the low-T magnetic phase is paraelectric, and the higher-T one is ferroelectric with a size and direction of polarization in good agreement with experiments. By mapping the ab initio results on to an effective spin model, we show that the system has a manifold of almost degenerate ground states. In the high-T magnetic state noncollinearity and inversion symmetry breaking stabilize each other via the Dzyaloshinskii-Moriya interaction. This leads to an unconventional mechanism for multiferroicity, with the particular property that nonmagnetic impurities enhance the effect.
authors.affiliation: Consiglio Nazionale delle Ricerche CNR-SPIN L'Aquila, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Giovannetti
authors.forename: Sanjeev
authors.initials: S
authors.lastname: Kumar
authors.forename: Alessandro
authors.initials: A
authors.lastname: Stroppa
authors.forename: Jeroen
authors.initials: J
authors.lastname: van den Brink
authors.forename: Silvia
authors.initials: S
authors.lastname: Picozzi
authors.forename: José
authors.initials: J
authors.lastname: Lorenzana