Observation of Spin-Induced Ferroelectricity in a Layered van der Waals Antiferromagnet CuCrP₂S₆

CuCrP₂S₆, a van der Waals magnet having stacked layers of 2D honeycomb lattice made of CuS₃ triangles and CrS₆ octahedra, exhibits an A-type antiferromagnetic order with the Néel temperature (T_N) = 32 K. Upon in-plane magnetic field (H) being applied below T_N, H-induced modulation of the c*-axis electric polarization (ΔP_c*) is found at fields lower than the saturation field µ₀H_S = 6.1 T, at which a forced ferromagnetic alignment sets in. Based on the symmetry analyses and dependence of ΔP_c* on H and the azimuthal angle of applied H direction, a microscopic origin of the magnetoelectric (ME) coupling is attributed to the spin-direction-dependent p–d hybridization that is allowed due to the presence of off-centered Cr³⁺ octahedra. A comparative study on CuCrP₂Se₆, however, finds no H-induced P modulation due to cancellation of P between neighboring layers with the doubling of a crystallographic unit cell at T_N. As the p–d hybridization mechanism allows generation of P in a single Cr atom–ligand pair, the results imply that large ME coupling should exist even in a single layer limit of CuCrP₂S₆.