Anisotropic dielectric and ferroelectric response of multiferroic LiCu2O2 in magnetic field

TL;DR

This study investigates the anisotropic dielectric and ferroelectric responses of high-quality LiCu2O2 crystals under magnetic fields, providing evidence for a new helimagnetic structure and highlighting the use of dielectric measurements to probe complex spin orders.

Contribution

The paper presents the first systematic investigation of dielectric and ferroelectric behaviors in LiCu2O2 under magnetic fields, supporting a novel helimagnetic model with a diagonal spin helix plane.

Findings

Strong anisotropic dielectric and ferroelectric responses observed.

Evidence supports a new helimagnetic model with diagonal spin helix plane.

Dielectric measurements can effectively probe complex spin structures.

Abstract

LiCu2O2 is the first multiferroic cuprate to be reported and its ferroelectricity is induced by complex magnetic ordering in ground state, which is still in controversy today. Herein, we have grown nearly untwinned LiCu2O2 single crystals of high quality and systematically investigated their dielectric and ferroelectric behaviours in external magnetic fields. The highly anisotropic response observed in different magnetic fields apparently contradicts the prevalent bc- or ab- plane cycloidal spin model. Our observations give strong evidence supporting a new helimagnetic picture in which the normal of the spin helix plane is along the diagonal of CuO4 squares which form the quasi-1D spin chains by edge-sharing. Further analysis suggests that the spin helix in the ground state is elliptical and in the intermediate state the present c-axis collinear SDW model is applicable with some appropriate modifications. In addition, our studies show that the dielectric and ferroelectric measurements could be used as probes for the characterization of the complex spin structures in multiferroic materials due to the close tie between their magnetic and electric orderings.