Magnetoelastic and Magnetoelectric Coupling in Two-Dimensional Nitride MXenes: A Density Functional Theory Study.

Two-dimensional multiferroic (2D) materials have garnered significant attention due to their potential in high-density, low-power multistate storage and spintronics applications. MXenes, a class of 2D transition metal carbides and nitrides, were first discovered in 2011, and have become the focus of research in various disciplines. Our study, utilizing first-principles calculations, examines the lattice structures, and electronic and magnetic properties of nitride MXenes with intrinsic band gaps, including VNF, VNO, CrNF, MoNO, MoNF, and MnNO. These nitride MXenes exhibit orbital ordering, and in some cases the orbital ordering induces magnetoelastic coupling or magnetoelectric coupling. Most notably, CrNF is a ferroelastic material with a spiral magnetic ordered phase, and the spiral magnetization propagation vector is coupled with the direction of ferroelastic strain. The ferroelectric phase can exist as an excited state in VNO, CrNF, and MoNF, with their magnetic order being coupled with polar displacements through orbital ordering. Our results also suggest that similar magnetoelectric coupling effects persist in the Janus MXenes VNOF, CrNFO, and MoNFO. Remarkably, different phases of MoNFO, characterized by orbital ordering rearrangements, can be switched by applying external strain or an external electric field. Overall, our theoretical findings suggest that nitride MXenes hold promise as 2D multiferroic materials.