Preparation and multiferroicity of a novel two-dimensional material NiH₂SeO₄

Two-dimensional materials have rich physical and chemical properties due to their unique nanostructures and electronic states. Although many two-dimensional materials have been reported in the past decade, they rarely exhibit multiferroic behavior. Herein, we synthesized layered structure NiH2SeO4 single crystals using the hydrothermal method, which can be further exfoliated into nanosheets using the transparent glue method. In addition, we demonstrated using first-principles calculations that the dissociation energy and dissociation strength of NiH2SeO4 crystals are much lower than those of graphite, and the single layer is multiferroic. The monolayer NiH2SeO4 is mainly polarized along the in-plane axis, and the polarization is comparable to the bulk material of BaTiO3. Furthermore, NiH2SeO4 exhibits antiferromagnetic transition at 24 K, and the effective moment of Ni2+ is 3.32 μB. The monolayer NiH2SeO4 is antiferromagnetic and the easy axis is along the in-plane (100) direction. NiH2SeO4 represents one of a few two dimensional multiferroic materials, and this study provides an approach for obtaining two dimensional multiferroic materials by incorporating magnetic ions with ions with lone pairs.