Observation of charge–transfer–driven antiferroelectricity in 3d-pyrochlore multiferroic Cu2OCl2

Abstract

Very recently, multiferroic behavior close to the boiling temperature of liquid nitrogen was reported in oxohalide-based Cu2OCl2. In this study, we have established yet another novel mechanism for the origin of charge ordering in multiferroic Cu2OCl2. The direct current (DC) magnetization, specific heat, and neutron diffraction measurements confirm the antiferromagnetic (AFM) ordering (TN) of Cu2OCl2 near 70 K. The collinear AFM spin structure in Cu2OCl2 was obtained from neutron powder diffraction experiments based on the fitting to the combination of two irreducible representations—Г1⊕Г2. Electrical properties, such as dielectric constant, pyroelectric current, and polarization-electric field hysteresis-loop measurements, together suggest a long-range antiferroelectric ordering near TE ≈ 75 K. The charge transfer from Cl to O along the c-axis was found to induce antiferroelectricity near TE and is supported from ab initio calculations. This finding largely reduces the possibility of well-known Dzyaloshinskii–Moriya interaction in the observed multiferroic behaviors and provides insight into the various origins of high-TC multiferroics.