Spin-Chirality-Driven Ferroelectricity on a Perfect Triangular Lattice Antiferromagnet

Abstract

Magnetic field (B) variation of the electrical polarization P(c) (∥c) of the perfect triangular lattice antiferromagnet RbFe(MoO(4))(2) is examined up to the saturation point of the magnetization for B⊥c. P(c) is observed only in phases for which chirality is predicted in the in-plane magnetic structures. No strong anomaly is observed in P(c) at the field at which the spin modulation along the c axis, and hence the spin helicity, exhibits a discontinuity to the commensurate state. These results indicate that the ferroelectricity in this compound originates predominantly from the spin chirality, the explanation of which would require a new mechanism for magnetoferroelectricity. The obtained field-temperature phase diagram of ferroelectricity agree well with those theoretically predicted for the spin chirality of a Heisenberg spin triangular lattice antiferromagnet.

High-field magnetic structure of the triangular antiferromagnet RbFe(MoO4)2

“…4 to be covered. Each of the magnetic reflections seen at the ( 1 3 1 3 q z ) and ( 2 3 2 3 q z ) positions with q z ≈ ± 1 2 , consist of two incommensurate peaks, q z = 0.458 and q z = 0.542, as observed in previous neutron diffraction experiments [5,7,8], however, the Q-resolution of the EXED instrument in forward scattering did not allow us to fully resolve the peaks.…”

“…RbFe(MoO 4 ) 2 orders magnetically below T N ≈ 3.8 K [1]. The magnetic structures found for the inplane field orientation using a variety of experimental methods [1][2][3][4][5][6][7][8][9] are schematically depicted in Fig. 3, the sequence shown corresponds to an increasing magnetic field.…”

“…The magnetic phases of RbFe(MoO 4 ) 2 were studied at several positions on the H − T phase diagram (Fig. 5) by neutron diffraction experiments [5,7,8]. The study of the 120 • phase at H = 0, T = 2 K shows that the value of the ordered component of magnetic moment is 3.9(5)µ B , or 0.78gµ B S. For the UUD phase studied at µ 0 H = 6 T, T = 2 K, the ordered component of the magnetic moment is 3.3(3)µ B [5] or 0.66gµ B S. Combining these results with the magnetic moment measured at the same conditions, M = 1.6(5)µ B /Fe 3+ [2], the uniform magnetization can be evaluated as 0.5µ B /Fe 3+ or 0.1gµ B S. The V phase (Fig.…”

“…In this compound the antiferromagnetic inter-planar exchange interaction J ′ is much weaker than the dominant in-plane interaction, J. For a magnetic field applied within the triangular plane, a sufficiently strong single-ion easy-plane anisotropy leads to a strong resemblance between the main features of the H − T phase diagram for RbFe(MoO 4 ) 2 [1][2][3][4][5][6][7][8][9] and the model phase diagram of the XY 2D triangular lattice antiferromagnet (TLAF) studied in detail in Refs. [10][11][12][13].…”

Experimental evidence of symmetry breaking in the multiferroic Ba3NbFe3Si2O14 using sound velocity measurements

“…It is now well established that antiferromagnets with triangular lattices potentially show strong magnetoelectric coupling [1][2][3][4][5]. Due to magnetic frustration with first neighbor antiferromagnetic interactions, these systems normally favor the in-plane 120 • antiferromagnetic state which can induce an electric polarization via various mechanisms [5][6][7][8]. In some of these systems, the 120 • magnetic arrangement possesses two reversed directions of rotation around the triangle, defined hereafter as triangular chirality [9].…”