Ferroelectricity induced by proper-screw type magnetic order

A novel type of magnetic origin of ferroelectric polarization is proposed. In crystals with triclinic, monoclinic, or trigonal (rhombohedral) symmetries, the proper screw type of magnetic ordefing can induce ferroelectricity through the variation in the metal-ligand hybridization with spin-orbit coupling. The ferroelectric polarization in delafossite compounds Cu(Fe,Al)O-2 is successfully explained by the mechanism. The relation