Magnetoelectric effect in the honeycomb-lattice antiferromagnet BaNi₂(PO₄)₂

Magnetoelectric materials exhibit induction of magnetization by an electric field or polarization by a magnetic field, which is promising for various applications. Here, we report a comprehensive investigation of the structural, magnetic, and electrical properties in a quasi-two-dimensional planar antiferromagnet BaNi₂(PO₄)₂, which crystallizes in the rhombohedral structure (space group R-3) consisting of honeycomb layers of Ni²⁺ ions. Magnetic susceptibility and heat capacity data reveal a long-range antiferromagnetic ordering of Ni²⁺ ions at T_N = 24 K. Interestingly, an applied magnetic field induces a dielectric anomaly and an electric polarization at T_N with the polarization proportional to the applied magnetic fields, demonstrating the linear magnetoelectric effect in BaNi₂(PO₄)₂ with a coupling coefficient of 1.67 ps/m. It is interesting to note that the magnetic symmetry associated with the magnetoelectric effect is -1', which allows all tensor elements of the magnetoelectric susceptibility.