Spin-Order-Induced Ferroelectricity and Magnetoelectric Effect in LiCuFe2 (VO4)3

Abstract

The mixed spin chain compound, LiCuFe2(VO4)3, reaches a magnetically ordered state in two steps at TN2=9.8K and TN1=8.2K detected in magnetic-susceptibility χ and specific-heat Cp measurements. Dielectric permittivity ϵ evidences these transitions by a sharp peak at TN2 and a steplike anomaly at TN1, both easily suppressed by an external magnetic field. These features in permittivity are preceded by a frequency-dependent relaxation-type anomaly at T- insensitive to the magnetic field. Mössbauer spectroscopy reveals a wide distribution of a hyperfine field between TN2 and TN1 while the first-principles calculations provide values of magnetic-exchange-interaction parameters. For Cu, the orbital moment aligned in the same direction as the spin moment is substantial. This large orbital moment is important in driving the polarization through an inverse Dzyaloshinksii-Moriya interaction in a situation where the spatial symmetry gets broken in the magnetic structure. The data obtained suggest the spin-order-induced ferroelectricity is inherent for improper multiferroics. © 2018 American Physical Society.