Ferroelectricity induced by a combination of crystallographic chirality and axial vector

Nagai, Takayuki*; Hagihara, Masato   ; Yokoi, Rie*; Moriwake, Hiroki*; Kimura, Tsuyoshi*

Ferroelectric materials compatible with magnetism and/or conductive properties provide a platform for exploring unconventional phenomena, such as the magnetoelectric effect, nonreciprocal responses, and nontrivial superconductivity. Though recent studies on multiferroics have offered several approaches, the search for magnetic and/or conducting ferroelectric materials is still a challenging issue under the traditional "d-ness" rule, refusing active d electrons. Here, we propose the emergence of ferroelectricity through a combination of crystallographic chirality and axial vector, accepting even non-d magnetic ions. This proposal is demonstrated in quasi-one-dimensional magnetic systems SrMVO (M = Ni, Mg, and Co). The ferroelectric phase transition is observed by measurements of neutron powder diffraction and dielectric properties in all compositions. Structural analyses and first-principles calculations indicate that these magnetic compounds are identified as proper-type ferroelectrics whose ferroelectric phase transition is achieved by spiral motions of crystallographic screw chains formed by edge-shared MO6 octahedra, considered as the combination of locally defined chirality and axial vector. Computationally predicted magnitude of spontaneous polarization of SrMVO reaches 10C/cm, comparable to that of conventional ferroelectrics, despite the incorporation of non-d magnetic elements. The mechanism proposed in this study offers a unique approach to the exploration of new ferroelectrics beyond the traditional paradigms.