Incommensurate Orbital Modulation behind Ferroelectricity inCuFeO2

Abstract

CuFeO(2) is one of the multiferroic materials and is the first case that the electric polarization is not explained by the magnetostriction model or the spin-current model. We have studied this material using soft x-ray resonant diffraction and found that superlattice reflection 0 1-2q 0 appears in the ferroelectric and incommensurate magnetic ordered phase at the Fe L(2,3) absorption edges and moreover that the rotation of the x-ray polarization such as from σ to π or from π to σ is allowed at this reflection. These findings definitely provide direct evidence that the 3d t(2g↓) orbital state of Fe ions has a long-range order in the ferroelectric state. The spin-orbit interaction in Fe ions plays a crucial role to the ferroelectricity in CuFeO(2), coupling two nontrivial spin and orbital orders, both of which break the crystal symmetry.

Magnetochiral dichroism resonant with electromagnons in a helimagnet

“…The relation between the symmetry and the observed ME effect is worthy of consideration. The centrosymmetric crystallographic structure ðR 3 À mÞ in the paramagnetic phase turns out to be a chiral lattice structure (P1 or P2) in the screw spin phase through the spin-orbit interaction 40,41 . Since the screw axis along the magnetic modulation vector q m is the only symmetry element that can survive under application of the magnetic field (H ex // q m // z), some off-diagonal components (a xy and a yx ) and diagonal components of the ME tensor should become nonzero.…”

Hydrothermal synthesis of delafossite CuFeO2 crystals at 100 °C

“…[1][2] Nowadays, CuFeO2 is a p-type semiconductor of delafossite oxides and it has attracted much attention as a p-type TCO (Transparent Conducting Oxide) used for several applications such as transparent diodes, photocatalysts, photovoltaics, ferroelectrics and so on. [3][4][5][6][7] Generally, the CuFeO2 powders could be synthesized through high temperature solid state reactions under an inert gas environments (Ar or N2) at 900-1200°C , because of Cu + is more stable than Cu 2+ at high temperature. However, the solid state reaction or sol-gel method need an posttreatment at high temperature, [8][9] and the high temperature is a serious defect for these preparation methods.…”

Anisotropic lattice dynamics and intermediate-phase magnetism in delafossiteCuFeO2

“…The magnetic phase diagram of CuFeO 2 proves to be particularly rich with various magnetic phases at low temperatures, high magnetic fields [1][2][3][4], and high pressures [5,6]. Ferroelectricity [7] in CuFeO 2 and its connection to the magnetic order is the subject of ongoing studies [8,9].…”