General Theory for the Ferroelectric Polarization Induced by Spin-Spiral Order

Abstract

The ferroelectric polarization of triangular-lattice antiferromagnets induced by helical spin-spiral order is not explained by any existing model of magnetic-order-driven ferroelectricity. We resolve this problem by developing a general theory for the ferroelectric polarization induced by spin-spiral order and then by evaluating the coefficients needed to specify the general theory on the basis of density functional calculations. Our theory correctly describes the ferroelectricity of triangular-lattice antiferromagnets driven by helical spin-spiral order and incorporates known models of magnetic-order-driven ferroelectricity as special cases.

Improper ferroelectricity in helicoidal antiferromagnet Cu3Nb2O8

“…Therefore, polarization P is confined to plane of spin rotation and is perpendicular to propagation vector of incommensurate spin orderings. In recent years, particularly after the discovery of multiferroicity in MnI 2 and CuFeO 2 , it is believed that KNB model may not be appropriate for several helicoidally ordered spinfrustrated multiferroics [10,11].…”

General microscopic model of magnetoelastic coupling from first principles

“…Schematic illustration of three contributions to the electric polarization induced by a spinorder in multiferroics. The pure electronic contribution [19,21,22] arises from the electron density redistribution induced by the spin-order. For the ion-displacement part, it results from the ion displacements caused by the induced forces associated with a spin order [20,24].…”

“…(3) may be greatly reduced. 5 Previously, it was shown [19][20][21][22][23][24][25] that spin-order induced electric polarization contains a pure electronic contribution and an ion-displacement related contribution (see Fig. 1).…”

Ferrielectricity in DyMn2O5: A golden touchstone for multiferroicity of RMn2O5 family

“…1(a) and 1(b) for a guide of eyes where a charge-ordered spin chain is chosen for illustration, although other mechanisms for individuals were proposed. [15][16][17] Details for discovering these phenomena and relevant physics can be found in several recent review papers. 1,3 Figure 1(a) shows a noncollinear spin chain where a spin-pair is bridged by a ligand ion (e.g., oxygen O) and the spins are noncollinearly ordered in counterclockwise spiral (a1) or clockwise spiral (a2) alignment.…”